TcLip Structural & Thermal Design Calculations

TcLip™ Structural & Thermal Design Calculations

E n g i n e e re d A s s e m b l i e s I n c .

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Version 2.0 brilliant buildings

Guide des caractéristiques thermiques et structurales du TcLip MC d’Engineered Assemblies Une version en français de ce document n’est pas disponible à l’heure actuelle.

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Table of Contents E n g i n e e re d A s s e m b l i e s I n t ro d u c t i o n E n g i n e e re d A s s e m b l i e s E x e c u t i v e S u m m a r y Q u i c k R e f e re n c e s E ff e c t i v e R Va l u e S e l e c t i o n G u i d e C h a r t Isometric Detail T 1 0 0 T h e r m a l Wa l l S y s t e m D e t a i l s T 1 2 5 T h e r m a l Wa l l S y s t e m D e t a i l s T 1 5 0 T h e r m a l Wa l l S y s t e m D e t a i l s

6 7 8 9 10

R e a d J o n e s C h r i s t o ff e r s e n S t r u c t u r a l R e p o r t I n t ro d u c t i o n Wo r k e d E x a m p l e ( f i g u re 0 1 ) A rc h i t e c t u r a l D e s i g n C h a r t s ( f i g u re s 0 2 - 0 4 ) E n g i n e e r i n g D e s i g n C h a r t s ( F i g u re s 0 5 - 0 7 ) Thermal Images Summary

12 13 14 17 20

Morrison Hershfield Thermal Report 1.

I n t ro d u c t i o n 2.

M o d e l i n g P ro c e d u re s 3.

Thermal Analysis 3.1 Clear Field Thermal Performance 3.2 S l a b E d g e L i n e a r Tr a n s m i t t a n c e 3.3 Impact of Batt Insulation in Steel Stud Cavity 4.

Sensitivity Analysis 4.1 I n s u l a t i o n Ty p e 4.2 Clip Spacing 5.

B u i l d i n g E n v e l o p e R e q u i re m e n t s i n C a n a d a 6.

Conclusion

22 22 22 23 23 25 26 26 27 28 32

Appendix Appendix Appendix Appendix

33 40 47 51

A B C D

– – – –

C l i p S y s t e m D e t a i l s a n d M a t e r i a l P ro p e r t i e s Ashrae 1365-RP Methodology E ff e c t i v e A s s e m b l y R - Va l u e s E x a m p l e S i m u l a t e d Te m p e r a t u re D i s t r i b u t i o n

3 4

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T c L i p ™ R V R S WA L L S Y S T E MEngineered Assemblies Inc.

6535 Millcreek Drive, Unit 75 Mississauga, Ontario, Canada L5N 2M2

Engineered Assemblies Unites the House of Design to The Field of Construction We are pleased to provide you thermal and structural testing and analysis for TcLip™; Thermally BrokenPartnership Subsystem with a variety Experience Success through with for our use Services: of facades including: fibre cement, solid phenolic, ceramic, wood veneer, porcelain, etc. • We collaborate on design; providing value engineering, mockups,

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OUR PARTNERS

™

samples, lunch and learns, webinars, etc.

• We provide extensively-detailed, stamped shop drawings.

INTRODUCTION • We offer complete system supply.

This guide provides thermal and structural analysis of Engineered Assemblies’ TcLip™; Thermally Subsystem.

TcLip™ofsystem Engineered AssembliesBroken understands and promotesThe the philosophy partnership.

We maintain a cooperative presence and focus achieving supports a variety of façade panels.

The main purpose of on this guide is the desired goal; completing a project on time and on budget to the to create a better understanding of the performance capabilities and highest of industry standards. benefits of TcLip™.

We take a common-sense approach to systems development; offering functional assemblies that are cost effective without compromising the Refer to the “Quick References” section of this guide for a breakdown designer's intent. of performanceFrom details and system drawings.

System drawings 1, 2 and detailing to field installation practicality, our 20 years of experience provide a keen eye on the design and strong handle on the limiting factors 3 (pgs. 8-10) detail Engineered Assemblies Hidden Fastening system. of the field.

DISCLAIMER OUR SYSTEMS: The use of this information shows your acceptance of these terms. The information is intended to provide background • TcLip Thermally Broken Subsystem information on Engineered • Hidden Fastener System (HF) specifically TcLip™; Thermally Assemblies building envelope systems; • Rear Ventilated Rain Screen (RVRS) Broken Subsystem with reference to theSystems Hidden Fastener System.

OUR PRODUCTS:

Although Engineered Assemblies Inc. makes reasonable efforts to present information which is up to date and accurate. Engineered Assemblies • Equitone Fibre Cement façade Inc. makes no •representation or warranty Parklex Natural Wood façade as to the adequacy, accuracy Savoia Porcelainoffaçade completeness •or correctness such information, nor does it warrant or Ceramic provided façade represent that •theTonality information is complete in every respect.

• VIVIX Solid Phenolic façade • Corten, Zinc, Copper, Stainless Steel & Aluminum façade Engineered Assemblies Inc. shall not have liability resulting from the use • CPI Daylighting solutions of the information provided, theand absence of any specific information, the • Imetco Metal roof wall systems

possible interruptions or technical errors of this information and/or the content herein.

Your Engineered Assemblies Inc. Team

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E n g i n eAssemblies e re d A s s e Inc. mblies Inc. Engineered

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June 21, 2012 Engineered Assemblies (EA) RVRS TcLip™ System Executive Summary In response to the rapidly increasing demand for Thermally Effective wall assemblies to meet the evolving National Building Code, EA has designed a Thermal Clip System.

EA RVRS T-Clip System comes in three clear field clip options; T100, T125 and T150, which accommodate 4”, 5”, and 6” of exterior mineral wool insulation (R-4.2/inch) respectively.

The system is comprised of aluminum clips connected to horizontal and vertical subgirts (framing members) that support Rear Ventilated Rain-Screen (RVRS) cladding panels. The clips are designed to attach to a steel stud back-up wall.

Thermal Performance The RVRS TcLip™ System meets the prescriptive requirements for non-residential steel stud walls in ASHRAE 90.1-2007/2010 for all climate zones. Performance of the system is validated through Modeling and the Finite Element Analysis (FEA) package completed by Morrison Hershfield. The thermal solver and modeling procedures utilized for this study were extensively calibrated and validated for ASHRAE Research Project 1365-RP “Thermal Performance of Building Envelope Details for Mid- and HighRise Construction (1365-RP)1. (for full report reference attached Report No. 5123226.00 dated March 22, 2012) Structural Performance The RVRS TcLip™ System is engineered to accommodate Façade panels generally 826mm in thickness that require vertical back ventilation of minimum 25mm free air space. The system provides vertical framing members (reference EA drawing P1, part #292) that allow thermal expansion of both the vertical framing member and the movement of the panel. The vertical framing members are attached to horizontal framing members and may be positioned as required to accommodate panel fastener and vertical joint location. There is an EPDM gasket covering the face of the vertical framing member as a separator between the façade panel and the vertical Framing.

The horizontal framing member (reference EA drawing P1, part #216) attaches to the TcLip™ and can be adjusted to plumb out the structure. The spacing of the horizontal framing is adjustable to suite the design loads imposed on the system.

Note: all framing members are made of pre=painted Black Z275 Grade A Galvanized Steel.

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The RVRS TClip System is engineered to accommodate Façade panels generally 826mm in thickness that require vertical back ventilation of minimum 25mm free air space. The system provides vertical framing members (reference EA drawing P1, part E n g i n eand e re d the Assemblies Inc. #292) that allow thermal expansion of both the vertical framing member 3 5 horizontal Millcreek Drive, Unit 75 E . A . I . T of h Ethe r mpanel.

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6.2218 framing member as a separator between the façade panel and the Tvertical F 905.816.9761 The horizontal framing member (reference EA drawing P1, part #216) attaches to the TClip and can be adjusted to plumb out the structure. The spacing Eof ithe n f o @horizontal engineeredassemblies.com W EngineeredAssemblies.com framing is adjustable to suite the design loads imposed on the system.

Note: all framing members are made of pre=painted Black Z275 Grade A Galvanized Steel.

RVRS TcLip™ design The horizontal framing member attaches to an engineered 38mm wide die cut aluminum extruded TcLip™. (Reference EA drawing P1, item 401A) There are three different clip options; T100, T125 and T150. The size is determined by the thickness of insulation required. (For R-Value selection see attached Report No. 5123226.00 dated March 22, 2012) Thermal breaks are provided at the connection between the framing and clips via a cork/neoprene pad and between the clips and exterior sheathing via an Aerogel insulation pad. (See Figure 1 for a simplified rendering in attached “Mini Summary”) The clips are attached to a steel stud back-up wall, using minimum 2 and up to 4 corrosion resistant self-drilling screws. Location of the clip is determined by the design loads imposed on the system.

Summary

• • • • • • •

The EA RVRS TcLip™ System meets the requirements of ASHRAE 90.12007/2010 for all climate zones The EA RVRS TcLip™ System is designed for RVRS (Rear Ventilated Rain-Screen) façade The EA RVRS TcLip™ System is adjustable to plumb out structure and has adaptable vertical framing members The EA RVRS TcLip™ System is light weight manufactured using low embodied energy, Non-Combustible and recyclable components The EA RVRS TcLip™ System is “system integrated” design, supplied with Engineered Shop drawings The EA RVRS TcLip™ System is engineered for design strength of L/300 The EA RVRS TcLip™ System is designed to minimize Wind Washing, it is Mold and Fungi resistant, Versatile, Cost effective, installer Friendly and is proudly made in Canada

For further information please visit: www.engineeredassemblies.com

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T c L i p ™ R V R S WA L L S Y S T E M

Effective R Value Selection Guide Table 2: Clear Field Effective Thermal Resistance with no Interior Insulation Clip System (Inches of Mineral Wool)

Exterior Insulation Nominal R-Value hrˑft²ˑ˚F/BTU (m²K/W)

T100 (4”)

Assembly Effective R-Value hrˑft²ˑ˚F/BTU (m²K/W) EA Clip System

Continuous Vertical Girts @ 16” o.c.

Continuous Horizontal Girts @ 24” o.c.

Vertical/ Horizontal Girts @ 24” o.c.

17.2 (3.04)

10.1 (1.78)

11.9 (2.10)

13.2 (2.33)

20.4 (3.59)

20.8 (3.67)

11.1 (1.96)

13.5 (2.38)

15.4 (2.71)

23.8 (4.19)

24.4 (4.30)

11.9 (2.10)

14.5 (2.55)

18.4 (3.24)

34” Vertical Clip Spacing

41” Vertical Clip Spacing

48” Vertical Clip Spacing

16.8 (2.96)

16.4 (2.89)

16.9 (2.99)

T125 (5”)

21.0 (3.70)

19.6 (3.45)

T150 (6”)

25.2 (4.44)

22.7 (4.00)

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Structural Report

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In this section of the design guide we provide support in achieving the most effective use of the TcLip™. We present three design charts each for Architect/Designers and Engineers. The charts cover models ‘T100’, T125’ and ‘T150’.

The Architect/Designer charts (figure 02 to 04) allow for quick and simple evaluation of basic systems based on typical spacing. On the vertical axis of these charts you will find the design dead load or self-weight of the panel system you wish to use. The horizontal axis indicates the maximum allowable wind load for a given dead load.

The Engineer design charts (figure 05 to 07) allow the engineer to design the clips in a way that maximizes their utilization and can aid in designing an optimal system for their unique project needs.

See the worked example (figure 01).

Typical Stress Due to Dead Load on Clip

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Figure 01:

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Worked Example for a ‘T125’ Clip

In this example the panel that we are designing for has a dead load or self-weight of 1.25 kPa., and we want to know if the system can take a wind load of 35 PSF. We would like to have a space of 125mm (5”) so we can have 4” of insolation and 1” air space behind the panel. The layout of the girts are as shown on the design guide and spaced horizontally 16” apart and vertically 48” apart.

As we can see from the chart the maximum wind load in this case is over 101 PSF and well above the required 35 PSF and therefore the clip will work in this application.

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Figure 02:

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‘T100’ Thermal Wall System Mounting Clip Extrusion Loading Chart for Architect/Designers

General Notes: -

Loads are assumed to have a safety factor of 1.5 In accordance with CAN/CSA S157 Based on maximum extension of z-girt (18mm) Refer to Part 401E (Aluminum Alloy 6005A-T61) 16” (0.406m) x 48” (1.219m) Tributary Area

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Figure 03:

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‘T125’ Thermal Wall System Mounting Clip Extrusion Loading Chart for Architect/Designers

General Notes: -

Loads are assumed to have a safety factor of 1.5 In accordance with CAN/CSA S157 Based on maximum extension of z-girt (18mm) Refer to Part 401E (Aluminum Alloy 6005A-T61) 16” (0.406m) x 48” (1.219m) Tributary Area

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Figure 04:

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‘T150’ Thermal Wall System Mounting Clip Extrusion Loading Chart for Architect/Designers

General Notes: -

Loads are assumed to have a safety factor of 1.5 In accordance with CAN/CSA S157 Based on maximum extension of z-girt (18mm) Refer to Part 401E (Aluminum Alloy 6005A-T61) 16” (0.406m) x 48” (1.219m) Tributary Area

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Figure 05:

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‘T100’ Thermal Wall System Mounting Clip Extrusion Loading Chart for Engineers

General Notes: -

Loads are assumed to have a safety factor of 1.5 In accordance with CAN/CSA S157 Based on maximum extension of z-girt (18mm) Refer to Part 401A (Aluminum Alloy 6005A-T61)

sheet xiv

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Figure 06:

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‘T125’ Thermal Wall System Mounting Clip Extrusion Loading Chart for Engineers

General Notes: -

Loads are assumed to have a safety factor of 1.5 In accordance with CAN/CSA S157 Based on maximum extension of z-girt (18mm) Refer to Part 401A (Aluminum Alloy 6005A-T61)

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Figure 07:

6535 Millcreek Drive, Unit 75 6M5i3s 5s i sMs ial ul cgrae,eO k nDt ar ri vi oe, , CUanniat d7a5 E n g i n e e re d A s s e m b l i e s I n c .

ML 5i sNs i2sM s a2u g a , O n t a r i o , C a n a d a 6535 M millcreek Drive, U unit 75 LM m5iN s s 2i sM s a2u g a , O n t a r i o , C a n a d a T 905.816.2218 n 2M m2 L5N F 905.816.9761 T 905.816 ..881166. .29271681 FTtE 9i 9n00f o55@ engineeredassemblies.com F 905.816.9761 W EngineeredAssemblies.com E E info@engineeredassemblies.com info@engineeredassemblies.com assemblies.com W EngineeredA W EngineeredAssemblies.co m

‘T150’ Thermal Wall System Mounting Clip Extrusion Loading Chart for Engineers

General Notes: -

Loads are assumed to have a safety factor of 1.5 In accordance with CAN/CSA S157 Based on maximum extension of z-girt (18mm) Refer to Part 401E (Aluminum Alloy 6005A-T61)

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6535 Millcreek Drive, Unit 75 6M5i3s 5s i sMs ial ul cgrae,eO k nDt ar ri vi oe, , CUanniat d7a5 E n g i n e e re d A s s e m b l i e s I n c .

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REPORT

Thermal Performance of Engineered Assemblies Thermal Clips

Presented to:

Engineered Assemblies 6535 Millcreek Drive, Unit 76 Mississauga, Ontario, L5N2M2

Report No. 5123226.00

March 24, 2012

Morrison Hershfield | Suite 310, 4321 Still Creek Drive, Burnaby, BC V5C 6S7, Canada | Tel 604 454 0402 Fax 604 454 0403 | morrisonhershfield.com

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1. INTRODUCTION The Engineered Assemblies Thermal Clip System is an aluminum thermal clip system for attaching rain-screen cladding systems for steel stud wall assemblies with exterior insulation. Morrison Hershfield was contracted by Engineered Assemblies Inc. (E.A.I) to provide an overview of the energy codes in the major markets in Canada and evaluate the thermal performance of their thermal clip system for various scenarios.

The aluminum clips are connected to horizontal and vertical sub-girts that support rainscreen panel cladding. The clips are attached to a steel stud back-up wall. Thermal breaks are provided at the connection between the sub-girt and clips via a cork/neoprene pad and between the clips and exterior sheathing via an aerogel insulation pad. A summary of the components for the evaluated system follows and detailed drawings can be found in Appendix A.

2. MODELING PROCEDURES Modeling was done using the Nx software package from Siemens, which is a general purpose computer aided design (CAD) and finite element analysis (FEA) package. The thermal solver and modeling procedures utilized for this study were extensively calibrated and validated for ASHRAE Research Project 1365-RP “Thermal Performance of Building Envelope Details for Mid- and High-Rise Construction (1365-RP)1. The thermal transmittance (U-Value) or “effective R-value” was determined using the methodology presented in 1365-RP and is summarized in Appendix B.

3.

THERMAL ANALYSIS

The following section provides U-Value results for both the clear field area and an assembly including a typical floor slab detail. For effective assembly R-Values please see Appendix C.

3.1

Clear Field Thermal Performance

Three clear field assemblies were evaluated; the T100, T125 and T150 clip systems, which accommodate 4”, 5”, and 6” of exterior insulation respectively. Drawings for these systems, including dimensions and material properties are shown in Appendix A. Each of these systems was modeled for three vertical clip spacings and girt/sub girt arrangements as summarized in Table 1. The spacings are based on structural loading information provided by Engineered Assemblies Inc. Semi-rigid mineral wool, R-4.2 per inch (RSI-0.74 per 25 mm), was modeled outboard the exterior sheathing with 90 mm steel studs in the back-up wall spaced at 16” o.c.. A sensitivity analysis using other insulation types can be found in section 4 of this report. Table 2 shows the clear field U-values of the three clip systems and clip/girt spacing arrangements (Effective R-values are given in Table C.1). The horizontal spacing for the clips is always 16” o.c., since the clips are attached to the steel studs.

1

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Table 1: Horizontal Girt and Vertical Girt Spacing Structural Loading Scenario

Vertical Spacing of Clips (Inches)

Horizontal Girt Spacing (In)

Vertical Girt Spacing (Inches)

+/- 25 psf

48

48

23.5

+/- 35 psf

41

41

20.5

+/- 45 psf

34

34

17.5

Table 2: Clear Field Thermal Transmittance

Clip System

Exterior Insulation Nominal RValue

Assembly U-Value BTU/hr·ft2·oF (W/m2K)

hr·ft2·oF/BTU (m2K/W)

34” Vertical Clip Spacing

41” Vertical Clip Spacing

48” Vertical Clip Spacing

T100

16.8 (3.0)

0.061 (0.346)

0.059 (0.336)

0.058 (0.329)

T125

21.0 (3.7)

0.051 (0.288)

0.049 (0.278)

0.048 (0.272)

T150

25.2 (4.4)

0.044 (0.251)

0.042 (0.241)

0.041 (0.235)

The “effective R-value” of the clip systems are over 80% effective compared to the assembly nominal thermal resistance for all the clip systems. As with all systems with thermal bridging, the assembly is less effective with increasing insulation, but the diminishing returns is minor.

The results show that increasing the vertical spacing from 34 to 48 inches results in no more than a 7% reduction in the U-value (R-1.7 gain).

The vertical girts were spaced at specific intervals as determined by the structural loading.

However, the difference in positioning of the vertical girts between 15 to 25 inches for any of the scenarios has negligible effect on the overall thermal performance (less than 1%).

The temperature distribution for the T125 system at the horizontal sub-girt spaced at 41 inches is found in Appendix C. The absolute values are presented using temperature indices as defined in Appendix B.

3.2

Slab Edge Linear Transmittance

The slab edge detail evaluated for the thermal clip system has aluminum clips fastened to the slab and directly beneath the slab fastened to the steel stud wall. Drawings for this detail showing dimensions and material properties are found in Appendix A. The slab edge detail was modeled in the same manner as the previous section for three clip/girt arrangements. Table 3 summarizes the thermal performance values for a 9 foot floor

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to ceiling height (and 8 inch slab), including the effects of the slab edge detail for each clip system. Effective R-Values are given in Table C.2. Linear transmittance values are also provided, which allow the overall U-value to be calculated for any floor to ceiling height.

More information on utilizing linear transmittance is provided in Appendix A. The slab edge detail increases the overall U-value by approximately 10% (an R-2.4 reduction) compared to the clear field U-value for a 9 foot floor to ceiling height.

The linear transmittance values are not significantly impacted by the vertical clip spacing (at 34 inches, the clips are well isolated from the slab); therefore a single linear transmittance can represent any vertical clip spacing. There is a slight increase in linear transmittance from the T100 to T125 clip systems but none between the T125 to T150 systems. This effect was also evident in the slab edge details analyzed for 1365-RP and is discussed in detail in the final report. This is due to more heat flowing through the slab with increasing insulation levels up to maximum point It is reasonable to assign a single linear transmittance value of 0.04 BTU/hr·ft·oF (W/m K) to the slab edge for the thermal clip systems because the differences do not equate to significant difference is overall thermal performance. The temperature distribution for the T125 system with a 41 inch clip/girt spacing for the modeled slab edge detail can be found in Appendix D. Table 3: Overall Thermal Transmittance including the effects of an insulated slab edge for 9 foot floor to ceiling height

3.3

Clip System

Exterior Insulation Nominal R-Value hr·ft2·oF/BT U (m2K/W)

T100

Assembly U-Value with Slab Edge BTU/hr·ft2·oF (W/m2K)

Ψ Slab Edge Linear Transmittance BTU/hr·ft·oF (W/mK)

34” Vertical Spacing

41” Vertical Spacing

48” Vertical Spacing

16.8 (2.96)

0.064 (0.364)

0.062 (0.354)

0.061 (0.346)

0.029 (0.050)

T125

21.0 (3.70)

0.055 (0.312)

0.053 (0.303)

0.052 (0.297)

0.041 (0.070)

T150

25.2 (4.44)

0.048 (0.275)

0.047 (0.266)

0.046 (0.259)

0.041 (0.070)

Impact of Batt Insulation in Steel Stud Cavity

The stud cavities did not have any insulation in the scenarios presented in the previous sections. The impact adding R-12 batt insulation to the stud cavity was analyzed for the clear wall scenarios presented in section 3.1. The thermal transmittance values are summarized in Table 4. Effective R-values are given in Table C.3.

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Table 4: Clear Field Thermal Transmittance with Batt Insulation in the Stud Cavity

Clip System

Exterior Insulation Nominal RValue

Assembly U-Value with interior insulation BTU/hr·ft2·oF (W/m2K)

hr·ft2·oF/BTU (m2K/W)

34” Vertical Spacing

41” Vertical Spacing

48” Vertical Spacing

T100

16.8 (2.96)

0.045 (0.258)

0.044 (0.253)

0.044 (0.249)

T125

21.0 (3.70)

0.040 (0.225)

0.039 (0.220)

0.038 (0.215)

T150

25.2 (4.44)

0.036 (0.202)

0.035 (0.196)

0.034 (0.191)

Adding batt insulation to the stud steel cavity is often considered for during the design based on design constraints (cost or overall thickness) to meet specific building envelope thermal transmittance targets. However, adding batt insulation in the stud cavity is not as effective as adding insulation to the exterior for a clip system and the condensation resistance of the assembly will be greatly reduced. Table 5 summarizes the temperature indices (see appendix B) for the three clip systems with and without batt insulation in the stud cavity for 41” clip spacing. The significance of this is that split insulated assemblies have marginal condensation resistance compared to fully exterior insulated assembly2. The temperature distribution profile for the T125 system with a 41 inch clip/girt spacing with R-12 batt insulation in the steel stud cavity is found in Appendix D. Table 5: Minimum temperature indices for interior face of sheathing, with and without batt for 41” clip spacing Clip System

Without Batt Insulation

With Batt Insulation

T100

0.81

0.57

T125

0.83

0.64

T150

0.84

0.69

2

A thorough discussion on how to evaluate condensation resistance using temperature indices is available upon request

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4.

SENSITIVITY ANALYSIS

A sensitivity analysis of the modeled systems was performed to allow designers to interpolate the thermal performance values for others insulation levels and clip spacing.

4.1

Insulation Type

Effective Assembly R-Value (hr∙ft2∙oF/BTU)

The base modeling assumed semi-rigid insulation (R 4.2 / inch) for the exterior insulation.

Other conductivities were evaluated to allow the thermal transmittance values for the thermal clip system to be utilized for other types of insulation. In order to characterize the range of exterior insulation values, the modeled assemblies in section 3.1 were recalculated using a low end of R-3.5 per inch (RSI-0.62 per inch) to a high end of R-6.5 per inch (RSI-1.14 per inch). Figure 1 shows the graphical results for effective assembly RValue for a clip spacing of 41 inch for the varying R-per inch materials. The case of continuous exterior insulation as assumed in energy standard ASHRAE 90.1-2007 is also graphed as a reference.

45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.0 0.0

10.0

20.0

30.0

40.0

Nominal R-Value of Exterior Insulation (hr∙ft2∙oF/BTU) R-3.5 per inch

R- 4.2 per inch

R- 6.5 per inch

Continuous Insulation

Figure 1: Effective Assembly R-Value vs Nominal Insulation R-Value for a variety of insulation materials for 41 in clip spacing The results show that the thickness of the insulation (and length of the clip) for a given nominal thermal resistance is largely independent of the effective R-value. Therefore, the results can be characterized by the R-value of the exterior insulation and can be applied to any material. The results from Table 2 can be re-arranged and additional R-values can be interpolated with the results from the sensitivity analysis. The U-value results are presented in Table 6. Effective R-Values are given in Table C.4.

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As an example of how to use Table 6, look at a design that uses the T100 system with exterior sprayfoam and 41” clip spacing. 4” of sprayfoam (R-6.5 per inch) is equivalent to an exterior insulation nominal value of R-26 (RSI-4.58). Interpolating from Table 6 results in an assembly U-value of approximately U-0.042 (USI-0.237).

Table 6: Clip System Thermal Performance Per Exterior Insulation Level Exterior Insulation Nominal RValue

4.2

Assembly U-Value BTU/hr·ft2·oF (W/m2K)

hr·ft2·oF/BTU (m2K/W)

34” Clip Spacing

41” Clip Spacing

48” Clip Spacing

15 (2.64)

0.066 (0.373)

0.064 (0.363)

0.063 (0.356)

20 (3.52)

0.053 (0.300)

0.051 (0.291)

0.050 (0.284)

25 (4.40)

0.045 (0.254)

0.043 (0.244)

0.042 (0.238)

30 (5.28)

0.039 (0.221)

0.037 (0.212)

0.036 (0.206)

35 (6.16)

0.035 (0.198)

0.033 (0.189)

0.032 (0.183)

40 (7.04)

0.032 (0.180)

0.030 (0.171)

0.029 (0.165)

Clip Spacing

Several vertical clip spacing was analyzed for the T100 clip system for the base case of semi-rigid insulation with vertical spacing of the clips ranging from 27 to 55 inches. The Uvalue results are presented in Table 7. Effective R-values are given in Table C.5.

Table 7: T100 Clip Thermal Transmittance for Alternative Vertical Clip Spacing Exterior Assembly U-Value Insulation BTU/hr·ft2·oF (W/m2K) Nominal RValue hr·ft2·oF/BTU 27” Clip 34” Clip 41” Clip 48” Clip 55” Clip Spacing Spacing Spacing Spacing Spacing (m2K/W) 16.8 (2.96)

0.064 (0.365)

0.061 (0.346)

0.059 (0.336)

0.058 (0.329)

0.058 (0.329)

There is less than an R-2 difference in the effective R-value over the range of 27 in spacing to 55 in spacing. Increasing the spacing of the clips has a diminishing return and vertical clip spacing greater than 41 inches has a minimal impact.

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5.

BUILDING ENVELOPE REQUIREMENTS IN CANADA

For most provinces, the National Building Code of Canada is used as the basis for their respective building codes, with changes and implementations tailored for each province. For single family or low-rise (Part 9) buildings, provincial codes typically have their requirements for building envelope minimum insulation levels, however, for commercial or mid and high rise construction (non Part 9), many codes reference existing standards from national and international organizations. In regards to the building envelope, the most commonly referenced standards across Canada are ASHRAE 90.1 “Energy Standard for Buildings Except Low-Rise Residential Buildings” and the Model National Energy Code for Buildings (MNECB) 1997. The National Energy Code for Buildings (NECB) 2011 has recently been issued to replace MNECB 1997.

While these two standards differ in their specific requirements, they both employ three options for showing compliance: Prescriptive, Trade-off and Performance.

The prescriptive path awards compliance for explicitly meeting all provisions of the code relevant to the project in question. For the building envelope, assemblies must be lower than a given maximum thermal transmittance U-value or must meet or exceed insulation values in a prescribed assembly. These requirements can be based on climate region, building type/principal heating source and framing type, depending on the standard. The prescriptive path is widely used as it is fairly straight forward and building components need only be assessed individually. However, some of the prescriptive requirements may be difficult to achieve due to design trends. For example, in ASHRAE 90.1-2007, the prescriptive path requires a glazing to wall ratio of less than 40%. If these prescriptive requirements cannot be met, then another compliance path must be used.

The trade-off path allows for projects to trade-off the performance of building envelope components (i.e. roofs, walls, and windows) when the prescriptive requirements are not met for each and every item. With this approach, the performance of some envelope components may be lower than the prescribed values in the standard as long as other components exceed the requirements so that the overall building envelope is deemed to be equal or better than the standard. For example, this allows for low thermally performing walls if the roof sufficiently compensates above its prescriptive values. The trade-off method allows for some flexibility with the prescriptive values. This approach can be demonstrated using either specific calculations (provided in the standards) or through computer software that is typically provided by the authors of the standard.

The performance path requires an evaluation of the annual energy use of the whole building. This must be done using computer simulation, where the proposed building and its systems are modeled and compared to a compliance building. The compliance building contains the same shape, size, occupancy and scheduling of proposed building, but all of its systems and individual components meet the minimum requirements of the standard. For example, for the compliance building, the thermal performance of the walls of the compliance building must match the prescriptive U-values of the standard. The proposed design is acceptable if the annual energy use is less than or equal to that of the compliance building. Energy certification programs, such as Leadership in Energy and Environmental Design (LEED), have used MNECB and ASHRAE performance paths as this can allow for

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much greater flexibility in design. The performance path takes into account other variables such as building orientation, higher efficiency HVAC systems and lighting controls, which would not give any benefit with the other two compliance paths. Each standard gives requirements that specify what can and cannot be included with the energy model and which energy modeling programs can be used.

The Ontario Building Code (OBC) contains a supplementary standard SB-10 to deal with energy in non-Part 9 buildings. As of January 1st, 2012, SB-10 incorporates ASHRAE 90.12010; however the prescriptive path is modified by including the values from ASHRAE 189.1 “Standard for the Design of High Performance, Green Buildings” for envelope requirements.

For the performance path, compliance can be achieved by modeling energy savings 5% better than ASHRAE 90.1-2010, 25% better than MNECB 1997 or meeting ASHRAE 90.12010 modified by ASHRAE 189.1.

Currently, both the Alberta Building Code (ABC) and the Quebec Construction Code (CCQ) only have prescriptive values for minimum insulation levels in Part 9 buildings; however it does not contain any requirements for non Part 9 buildings. It is our understanding that both provinces are considering adopting NECB 2011 in order to assist in meeting their energy efficiency targets.

In British Columbia there are two governing documents. The majority of the province falls under the British Columbia Building Code (BCBC), while Vancouver follows the Vancouver Building Bylaw (VBBL). For non-Part 9 buildings, BCBC references ASHRAE 90.1-2004, while VBBL references the more recent ASHRAE 90.1-2007. The 90.1-2007 requirements are more stringent than 90.1-2004 (lower allowable glazing ratios, lower U-values, higher efficiency systems etc.), however the approach remains the same. The BCBC has recently adopted new energy efficiency requirements that allow a choice of compliance to either the ASHRAE 90.1-2010 or the NECB 2011. The effective date is December 20, 2013. VBBL will also likely update to at least the requirements in BCBC soon.

Table 8 summarizes the prescriptive wall assembly requirements from ASHRAE 90.1 2004, 2007 and 2010 for steel framed buildings along with wall assembly requirements from NECB 2011. Canadian climate zones in both ASHRAE and NECB are divided by heating degree days (HDD). NECB divides zones every 1000 HDD, however ASHRAE groups climate zones by 1000 or 2000 HDD. Both zone types are included.

ASHRAE 90.1 tends to be updated every 3 years. From this chart, it can be seen that the trend from 2004-2007 was to decrease the maximum U-value. The decrease in U-value appears to be based on increasing the amount of continuous exterior insulation. Adjusting the building envelope prescriptive requirements does not happen with every cycle (20072010 did not see further decreases to U-value); however ASHRAE 90.1 may choose to do so in the future as other standards, such as NECB 2011, already have more stringent prescriptive requirements.

Moving forward, to achieve realistic thermal performance goals, standards will need to begin to account for thermal bridging in details. Currently, many codes in Canada offer exemptions for the thermal effects of details (such as slab edges) or their inclusion is often left to interpretation by designers. For example, in the ASHRAE 90.1 performance path, slab edges are typically ignored as long as they are less than 5% of the wall area. Depending on the detail, these thermal bridges can have a major impact on the thermal performance of the building envelope.

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Table 8: Maximum Assembly U-Value Requirements for Prescriptive Paths Maximum Assembly U-Value

ASHRAE Climate Zone

NECB Climate Zones

Heating Degree Days (HDD)

ASHRAE 90.1-2004

ASHRAE 90.12007

ASHRAE 90.12010

NECB2011

4C

4

< 3000

0.084 (0.477)

0.064(0.363)

0.064(0.363)

0.055 (0.315)

5A, 5B and 5C

5

3000-4000

0.084 (0.477)

0.064 (0.363)

0.064(0.363)

0.049 (0.278)

6A, 6B

6

4000-5000

0.084 (0.477)

0.064 (0.363)

0.064 (0.363)

0.044 (0.247)

7A

5000-6000

0.064 (0.363)

0.064 (0.363)

7B

6000-7000

0.064 (0.363)

0.064 (0.363)

0.064 (0.363)

0.037 (0.210)

8

>7000

0.064 (0.363)

0.064 (0.363)

0.064 (0.363)

0.032 (0.183)

7

8

BTU/hr∙ft2∙oF (W/m2K)

0.064 (0.363)

0.037 (0.210)

For exterior insulated steel stud assemblies, that require cladding to be attached to the structure with structural members, must be less than a maximum assembly U-value3 to meet the prescriptive requirements for all the standards. The T-clip for all the evaluated clip spacings meets the U-value requirements with less insulation than the common site solutions as shown in Table 9 and Figure 2. These comparison systems are from the analysis done for ASHRAE Research Project 1365-RP. A summary of this work is found in Appendix B.

3

No exterior insulated wall system with cladding exists that satisfies the current definition of continuous insulation in the ASHRAE 90.1 standards, therefore only the U-value is relevant for all the performance paths.

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Table 9: Effective U-values for exterior Insulated Steel Stud Assemblies with Various Girt Attachments Clip System (Inches of Mineral Wool)

Exterior Insulation Nominal R-Value hr·ft2·oF/B TU (m2K/W)

T100 (4”) T125 (5”) T150 (6”)

16.8 (2.96) 21.0 (3.70) 25.2 (4.44)

Assembly U-Value BTU/hr·ft2·oF (W/m2K) E.A. T-Clip System 34” Vertical Clip Spacing 0.061 (0.346) 0.051 (0.288) 0.044 (0.251)

41” Vertical Clip Spacing 0.059 (0.336) 0.049 (0.278) 0.042 (0.241)

10

15

48” Vertical Clip Spacing 0.058 (0.329) 0.048 (0.272) 0.041 (0.235)

Continuous Vertical Girts @ 16” o.c.

Continuous Horizontal Girts @ 24” o.c.

Vertical/ Horizontal Girts @ 24” o.c.

0.099 (0.562) 0.090 (0.511) 0.084 (0.477)

0.084 (0.477) 0.074 (0.420) 0.069 (0.392)

0.076 (0.430) 0.065 (0.369) 0.054 (0.309)

35

Effective Assembly R-Value

30 25 20 15 10 5 0

0

5

20

25

30

Exterior Insulation Rated R-Value ASHRAE 90.1-2007 Continuous Insulation Vertical/Horizontal Girts Vertical Z-Girts

Intermittent, 36" Apart Horizontal Z-Girts E.A. T- Clip System, 34" Apart

Figure 2: Effective R-value for Selected Cladding Attachments with ASHRAE 90.1-2007 Minimum Climate Zone requirements for Residential and Non-Residential Buildings

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6.

CONCLUSION

From this report, the following conclusions can be made: •

For mineral wool insulation and the modeled thickness and clip spacing, the clip system assembly U-values range between 0.041 BTU/hr∙ft2∙oF - 0.061 BTU/hr∙ft2∙oF (0.235 W/m2K - 0.346 W/m2K).

•

With the inclusion of the proposed slab edge, the wall U-value is increased by, at most, 10% for the same range of clip size and spacing.

•

With the inclusion of interior R-12 batt, the clear wall thermal resistance gains approximately an effective R-5.5.

•

From the sensitivity analysis there is negligible effect of the insulation type on thermal resistance with the same the nominal R-value of the insulation. The results can be used for any type of insulation as long as the nominal R-value is known.

•

The clip spacing has a small effect on the thermal performance under 41”. Higher than 41”, the increase in thermal resistance is minor.

In terms of code compliance, the values given in this report can be used with all three compliance paths. For designers who are concerned with energy efficiency, beyond compliance, or as building codes change to include thermal bridging in details, the slab edge transmittance provided will assist in calculating a more accurate thermal performance of the building envelope.

Morrison Hershfield

Neil Norris, M.A.Sc. Building Science Consultant

Patrick Roppel, P.Eng. Associate, Building Science Specialist

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APPENDIX A – CLIP SYSTEM DETAILS AND MATERIAL PROPERTIES

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Engineered Assemblies Clip System

Component Interior Film Gypsum Board Air in Stud Cavity 3 5/8” x 1 5/8” Steel Studs Exterior Sheathing Exterior Insulation (Mineral Wool)

Clear Wall Assembly

Thickness

Conductivity

Nominal Resistance

0.09 (0.16) -

R-0.7 (RSI-0.12) R-0.5 (RSI-0.08) R-0.9 (RSI-0.16)

Inches (mm)

BTU/hr ·ft· oF (W/mK)

18 gauge

36 (62)

½” (13) 3 5/8” (92)

hr· ft2· oF/BTU (m2K/W)

-

½” (13) 0.10 (0.16) R-0.5 (RSI-0.08) R-16.8 to R-25.2 4” to 6” 0.020 (0.034) (RSI-2.96 to RSI-4.44) (102 to 152) 1/5” to 3/8” 92 (160) Aluminum Clip (5 to10) Aerogel 3/8” (10) 0.01(0.015) R-3.9 (RSI-0.68) Bolts 5/6”D (8D) 29(50) Cork/Neoprene pad 1/16” (1.5) 0.033 (0.058) R-0.15 (RSI-0.03) Horizontal Girt 16 gauge 36 (62) Vertical Girt 18 gauge 36 (62) Generic Cladding with ½” (13mm) vented air space is incorporated into exterior heat transfer coefficient Exterior Film R-0.7 (RSI-0.12) 35 4 page 2 p aDgEeC 3 5 0 63 O CT13 V 2.0

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Alternate Insulation Values Component R-12 Batt Insulation EPS Sprayfoam

Thickness

Inches (mm)

3 5/8” (92) 4” to 6” (102 to 152) 4” to 6” (102 to 152)

Conductivity

Nominal Resistance

0.025 (0.044)

R-12.0 (RSI-2.11) R-14.0 to R-21.0 (RSI-2.47 to RSI-3.70) R-26.0 to R-39.0 (RSI-4.58 to RSI-6.87)

BTU/hr ·ft· oF (W/mK)

0.024 (0.041) 0.013 (0.022)

hr· ft2· oF/BTU (m2K/W)

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Engineered Assemblies Clip System

Component Interior Film Gypsum Board Air in Stud Cavity 3 5/8” x 1 5/8” Steel Studs Exterior Sheathing Exterior Insulation (Mineral Wool)

Slab Edge Detail

Thickness

Conductivity

Nominal Resistance

Inches (mm)

BTU/hr ·ft· oF (W/mK)

hr· ft2· oF/BTU (m2K/W)

-

-

½” (13) 3 5/8” (92)

0.09 (0.16) -

R-0.6 to R-0.9 (RSI-0.11 to RSI-0.16) R-0.5 (RSI-0.08) R-0.9 (RSI-0.16)

18 gauge

36 (62)

-

½” (13) 0.10 (0.16) R-0.5 (RSI-0.08) R-16.8 to R-25.2 4” to 6” 0.020 (0.034) (RSI-2.96 to RSI-4.44) (102 to 152) 1/5” to 3/8” 92 (160) Aluminum Clip (5 to10) Aerogel 3/8” (10) 0.01(0.015) R-3.9 (RSI-0.68) Bolts 5/6”D (8D) 29(50) Cork/Neoprene pad 1/16” (1.5) 0.033 (0.058) R-0.15 (RSI-0.03) Horizontal Girt 16 gauge 36 (62) Vertical Girt 18 gauge 36 (62) Generic Cladding with ½” (13mm) vented air space is incorporated into exterior heat transfer coefficient Concrete Slab 8 (203) 1.04 (1.8) Exterior Film R-0.7 (RSI-0.12)

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T100 T100

T F

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a D j u s tm E nt r an g E + 5 - 1 5

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T125 T125

T F

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a D j u s tm E nt r an g E + 5 - 1 5

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T150 T150

T F

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a D j u s tm E nt r an g E + 5 - 1 5

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APPENDIX B – ASHRAE 1365-RP METHODOLOGY

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B.1

General Modeling Approach

For this report, a steady-state conduction model was used. Air cavities were assumed to have an effective thermal conductivity which includes the effects of cavity convection. Interior/exterior air films were taken from Table 1, p. 26.1 of 2009 ASHRAE Handbook – Fundaments depending on surface orientation. From the calibration in 1365-RP, contact resistances between materials were modeled. The temperature difference between interior and exterior was modeled as a dimensionless temperature index between 0 and 1 (see Appendix B.3). These values, along with other modeling parameters, are given in ASHRAE 1365-RP, Chapter 5.

B.2

Thermal Transmittance

The methodology presented in ASHRAE 1365-RP separates the thermal performance of assemblies and details in order to simplify heat loss calculations. For the assemblies, a characteristic area is modeled and the heat flow through that area is found. To find the effects of thermal bridges in details (such as slab edges), the assembly is modeled with and without the detail. The difference in heat loss between the two models is then prescribed to that detail. This allows the thermal transmittances to be divided into three categories: clear field, linear and point transmittances.

The clear field transmittance is the heat flow from the wall or roof assembly, including uniformly distributed thermal bridges that are not practical to account for on an individual basis, such as structural framing, brick ties and cladding supports. This is treated the same as in standard practice, defined as a U-value, Uo (heat flow per area). For a specific area of opaque wall, this can be converted into an overall heat flow per temperature difference, Qo. The linear transmittance is the additional heat flow caused by details that can be defined by a characteristic length, L. This includes slab edges, corners, parapets, and transitions between assemblies. The linear transmittance is a heat flow per length, and is represented by psi (Ψ).

The point transmittance is the heat flow caused by thermal bridges that occur only at single, infrequent locations. This includes building components such as pipe penetrations and intersections between linear details. The point transmittance is a single additive amount of heat, represented by chi (χ).

With these thermal quantities the overall heat flow can be found simple by adding all the components together, as given in equation 1.

Q = Σ Q thermalbri dge + Qo = Σ (Ψ ⋅ L )+ Σ (χ )+ Qo

EQ 1

Equation 1 gives the overall heat flow for a given building size. For energy modeling, or comparisons to standards and codes, often it is more useful to present equation 1 as a heat flow per area. Knowing that the opaque wall area is Atotal, and U=Q/Atotal, equation 2 can be derived.

U=

Σ (Ψ ⋅ L )+ Σ (χ ) +Uo ATotal

EQ 2

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Since the linear and point transmittances are simply added amounts of heat flow, they can be individually included or excluded depending on design requirements. The clear field analysis for R100, R125 and R150 clip systems is shown in Section 3.1. The linear transmittance analysis for the Engineered Assemblies clip system slab edge detail is shown in Section 3.2. For this report, no point transmittance details were analyzed.

B.2

Temperature Index

For condensation concerns, the thermal model can also provide surface temperatures of assembly components to help locate potential areas of risk. In order to be applicable for any climate (varying indoor and outdoor temperatures), the temperatures can been nondimensionalized into a temperature index, Ti, as shown below in Equation 3.

 =

 −   − 

EQ 3

The index is the ratio of the surface temperature relative to the interior and exterior temperatures. The temperature index has a value between 0 and 1, where 0 is the exterior temperature and 1 is the interior temperature. If Ti is known, Equation 3 can be rearranged for Tsurface.

Example temperature profiles for the assemblies and details modeled in this report are shown in Appendix C.

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SOLUTIONS

ion, , 65.

ms.

Thermal Bridging in Exterior Insulated Steel Stud Assemblies

BUILDINGS

Volume 2011, Issue 2

Leading the way to a Sustainable Future With a continued focus of sustainable and energy efficient building design, more attention is being paid to the

The Questions

thermal performance of building enclosure assemblies.

Building energy standards, such as ASHRAE 90.1, force recognition of the impact of thermal bridging. Table A3.3 in ASHRAE 90.1 provides effective assembly U values for stud walls that consider the effects of the steel studs through the stud cavity. These values, however, are for assemblies with different levels of continuous insulation outboard of the studs (basically assuming you have the full nominal value of the exterior insulation). The table does not provide guidance in addressing the thermal impact of the cladding support elements passing through the exterior insulation. This raises some critical questions: 1. What are the effective R- and U-values of your steel stud assembly walls and do they meet code requirements?

2. What is the difference in thermal performance of different cladding attachment arrangements?

Providing a higher level of thermal resistance in the building enclosure may seem as straightforward as just adding insulation, but when building with conductive elements like steel, achieving higher thermal performance levels can be elusive.

When cladding is attached to back up steel stud walls, the attachments

bypass

the

exterior

insulation.

These

attachments, usually made of steel, can create significant heat flow paths. While there are some systems that minimize the bridging effect, many of the common attachment methods are not very efficient from a thermal perspective.

s.

SOLUTIONS MH Volume 2011, Issue 2

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The SOLUTION Morrison Hershfield approached these questions as part of the ASHRAE Research Project 1365 “Thermal Performance of Building Envelope Details for Mid- and High-Rise Buildings”¹. Four different cladding attachment arrangements for exterior insulated steel stud cavities were investigated², using a well calibrated 3D thermal model³. These details are shown below:

1

2

VERICAL Z-GIRTS

VERTICAL and

INTERMITTENT Z-GIRTS

HORIZONTAL Z-GIRTS

SPACED 12”, 24” and 36” APART

HORIONTAL Z-GIRTS

Assembly U-Value BTU/hr ft 2 oF(W/m2K)

Exterior Insulation R-Value (RSI)

4

3

Vertical

Horizontal

Vertical/ Horizontal 5

36” apart

ASHRAE 90.1-2007 Continuous Insulation

Intermittent 12” apart

24” apart

5 (0.88)

0.157 (0.89)

0.146 (0.83)

n.a.

0.142 (0.81)

0.136 (0.77)

0.132 (0.75)

0.128 (0.73)

10 (1.76)

0.120 (0.68)

0.106 (0.60)

0.097 (0.55)

0.101 (0.57)

0.093 (0.53)

0.089 (0.50)

0.078 (0.44)

15 (2.64)

0.103 (0.59)

0.088 (0.50)

0.076 (0.43)

0.082 (0.47)

0.073 (0.41)

0.068 (0.39)

0.056 (0.32)

20 (3.52)

0.091 (0.52)

0.076 (0.43)

0.065 (0.37)

0.070 (0.40)

0.061 (0.35)

0.057 (0.32)

0.044 (0.25)

25 (4.40)

0.084 (0.47)

0.069 (0.39)

0.058 (0.33)

0.062 (0.35)

0.053 (0.30)

0.049 (0.28)

0.036 (0.20)

Effective R- and U- Values 4

The results of our modeling are shown in Table 1 . Since ASHRAE 90.1 is referenced by many building codes, the data is provided in a similar format – the effective clear wall U-value for varying amounts of exterior insulation. We have also provided, for comparison, ASHRAE 90.1 data for continuous insulation.

Figure 1 shows the data from Table 1, converted to effective R-value, and presented in a graphical format. Included with this figure are the prescriptive R-value requirements for ASHRAE 90.1-2007 for all climate zones for both residential and non-residential uses.

Figure 1: Effective Assembly R-Value for Selected Cladding Attachments with ASHRAE 90.1-2007 Minimum Climate Zone requirements for Residential and Non-Residential Buildings

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Adding Batt Insulation Adding Batt Insulation Often, fiberglass batt batt is added to filltothe cavity in order to to Often, fiberglass is added fill stud the stud cavity in order further increase the thermal resistance of anofexterior insulated further increase the thermal resistance an exterior insulated 8 8 evaluate the benefit of adding this steelsteel studstud assembly . To assembly . To evaluate the benefit of adding this insulation, we modeled the horizontal z-girtz-girt arrangement withwith insulation, we modeled the horizontal arrangement and and without an R-12 batt batt in the cavity. without an R-12 in stud the stud cavity.

The The results are shown in Figure 4. Adding the R-12 batt batt increases results are shown in Figure 4. Adding the R-12 increases the assembly R-value by, on R-7.5. the assembly R-value by,average, on average, R-7.5.

These results will differ using otherother systems; but only slightly.

In In These results will differ using systems; but only slightly. general, adding insulation in the cavity of anofexterior insulated general, adding insulation in stud the stud cavity an exterior insulated studstud wall wall assembly will add approximately 60%60% of the nominal assembly will add approximately of rated the rated nominal value of that insulation to the resistance of the value of that insulation to thermal the thermal resistance of assembly. the assembly.

ThisThis improvement maymay seem modest for the nominal improvement seem modest for increased the increased nominal R-value, but itbut may be important in meeting code.

R-value, it may be important in meeting code.

Figure 2: Thermal Gradients and heat flow paths for the selected cladding attachments 1) Vertical, 2) Horizontal, 3) Vertical/Horizontal

Figure 4 shows that that in order to meet the prescriptive requirements of of Figure 4 shows in order to meet the prescriptive requirements ASHRAE 90.190.1 using exterior insulation and and horizontal z-girts maymay ASHRAE using exterior insulation horizontal z-girts require the two layers of insulation. require the two layers of insulation.

Figure 2 shows temperature profiles for the modeled steel stud assemblies . These make it easier to visualize the heat flow paths created by the cladding attachments and steel studs. Comparing our modeled results and the 90.1 values for continuous exterior insulation shows that thermal bridging through the cladding attachments can have a very large effect on the overall heat loss through an assembly, particularly at higher levels of insulation. With the poorer performing systems, like vertical z-girts, the thermal bridging can result in over double the expected heat loss.

Horizontal Z-Girts without Horizontal Z-Girts without BattBatt insulation insulation

Comparing Assemblies

Horizontal Z-Girts with Horizontal Z-Girts with Batt insulation Batt insulation

For each of the modeled cases, there was a layer of gypsum sheathing separating the z-girts and the studs. The vertical z-girt system is commonly used because of the arrangementâ&#x20AC;&#x2122;s high structural strength. However, it is also thermally inefficient because the z-girts and steel studs are directly aligned, creating a straight path for heat to flow through the assembly.

With horizontal z-girts, the heat flow paths are less direct and the amount of steel overlap is greatly reduced when compared to the vertical z-girt system. This lowers the effective U-value; but only modestly since the z-girts still bypass the entire thickness of the exterior insulation. By using both vertical and horizontal z-girts, each z-girt only partially cuts through the insulation. With this arrangement, the heat flow paths are further reduced and result in a lower U-value than the previous two systems.

Continued on page 4 (back page)

Figure 4: Effective R-Values for Horizontal Z-Girts with and without interior Batt with ASHRAE 90.1-2007 Minimun Climate Zone requirements for Residential and Non-Residential Buildings

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This example provides understanding of the effects of 3D bridging in several ‘clear wall’ assemblies. In addition, there are other significant avenues of thermal bridging, including at parapets, slabs, corners etc. that were analyzed as part of the ASHRAE Research Project 1365.

As the push towards greater energy efficiency continues, 3D thermal modeling will become an increasingly useful approach in accurately analyzing the thermal performance of building envelope systems.

Figure 3: Effective Assembly R-Value for Intermittently spaced girts with ASHRAE 90.1-2007 Minimum Climate Zone requirements for Residential and Non-Residential Buildings.

3D thermal modeling is one of the many tools in MH’s toolbox, and combined with extensive field experience and knowledge, MH can effectively provide solutions that are relevant to the design, construction and operation of the building environment.

Supplementary Notes

For all these systems, there is a diminishing return to adding insulation, which can be seen in Figures 1 and 3. For example, going from an R-5 to an R-10 exterior insulation with the horizontal z-girt system, the thermal resistance is increased by R-2.6. If another R-5 of insulation is added, from R-10 to R-15, the thermal resistance this time is only increased by R-1.9.

Closing One of the important lessons of this analysis is that to achieve high levels of effective thermal resistance in steel stud walls, it is more important to find ways of eliminating, or thermally breaking the metal elements passing through the insulation. A number of systems have been proposed and used that make use of:

1. Report was finalized July, 2011 and is available at ashrae.org 2. For these 4 assemblies, the studs were 3.5in depths at 16”o.c. and the stud cavity was un-insulated.

The exterior insulation was varied from R-5 to R-25.

3. Part of MH’s resources is a 3D heat transfer model that was extensively calibrated and validated as part of the ASHRAE Research Project 1365.

4. These are the ‘clear wall’ U-values and includes the effects of the stud wall with no top and bottom tracks.

ASHRAE values were taken from ASHRAE 90.1-2007, Table A.3.3. Note that ASHRAE includes both top and bottom steel tracks

BUILDINGS

The fourth system is a set of intermittent clips that were modeled as 12” inch long pieces of z-girt, aligned vertically at the studs. Figure 3 compares the effect on R-values of the increased spacing and resultant reduction in metal passing through the insulation. With a widely spaced clip, this system gave the best thermal performance out of the four analyzed assemblies .

5. The vertical section of the vertical/horizontal system always contained R-5 insulation, and the horizontal section was varied between R-5 and R-25. A total value for an exterior insulation of R-5 alone is was not applicable.

6. All images shown are for an exterior insulation of R15.

7. This type of intermittent system is often constrained by structural considerations since the decrease in steel offers less support.

8. Other factors, such as condensation resistance, must also be considered when using batt insulation.

• structurally efficient cladding support systems • non metallic structural elements • low conductivity thermal breaks It is important to note that there are additional structural and fire resistance implications that need to be considered, as well the thermal performance, when using these systems.

If you wish to discuss how our services can help you make a difference, please contact us at buildingenvelope@morrisonhershfield.com or through your local Morrison Hershfield office with any questions.

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APPENDIX C – EFFECTIVE ASSEMBLY R-VALUES

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C1.

Clear Field Thermal Performance Table C.1: Clear Field Effective Assembly R-Values

Clip System

C2.

Exterior Insulation Nominal RValue

Assembly Effective R-Value hr·ft2·oF/BTU (m2K/W)

hr·ft2·oF/BTU (m2K/W)

34” Vertical Clip Spacing

41” Vertical Clip Spacing

48” Vertical Clip Spacing

T100

16.8 (3.0)

16.4 (2.89)

16.9 (2.98)

17.3 (3.04)

T125

21.0 (3.7)

19.7 (3.48)

20.4 (3.60)

20.9 (3.68)

T150

25.2 (4.4)

22.7 (3.99)

23.6 (4.15)

24.2 (4.26)

Slab Edge Thermal Performance

Table C.2: Effective Assembly R-Values including the effects of an insulated slab edge for 9 foot floor to ceiling height

Clip System

Exterior Insulation Nominal RValue hr·ft2·oF/BTU (m2K/W)

T100

Assembly Effective R-Value with Slab Edge hr·ft2·oF/BTU (m2K/W)

Ψ Slab Edge Linear Transmittance BTU/hr·ft·oF (W/mK)

34” Vertical Spacing

41” Vertical Spacing

48” Vertical Spacing

16.8 (2.96)

15.6 (2.75)

16.1 (2.83)

16.4 (2.89)

0.029 (0.050)

T125

21.0 (3.70)

18.2 (3.20)

18.8(3.30)

19.1(3.37)

0.041 (0.070)

T150

25.2 (4.44)

20.6 (3.63)

21.4 (3.76)

21.9 (3.86)

0.041 (0.070)

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C3.

Impact of Batt Insulation in Steel Stud Cavity

Table C.3: Clear Field Effective Assembly R-Values with Batt Insulation in the Stud Cavity

Clip System

C4.

Assembly Effective R-Value with interior insulation

Exterior Insulation Nominal RValue

hr·ft2·oF/BTU (m2K/W)

hr·ft2·oF/BTU (m2K/W)

34” Vertical Spacing

41” Vertical Spacing

48” Vertical Spacing

T100

16.8 (2.96)

22.0 (3.87)

22.5 (3.96)

22.8 (4.02)

T125

21.0 (3.70)

25.2 (4.44)

25.8 (4.55)

26.4 (4.65)

T150

25.2 (4.44)

28.1 (4.95)

28.9 (5.09)

29.7 (5.23)

Sensitivity Analysis Table C.4: Clip System Effective Assembly R-Value Per Exterior Insulation Level Exterior Insulation Nominal RValue

Assembly Effective R-Value hr·ft2·oF/BTU (m2K/W)

hr·ft2·oF/BTU (m2K/W)

34” Clip Spacing

41” Clip Spacing

48” Clip Spacing

15 (2.64)

15.2 (2.68)

15.7 (2.76)

16.0 (2.81)

20 (3.52)

18.9 (3.33)

19.5 (3.44)

20.0 (3.52)

25 (4.40)

22.4 (3.94)

23.2 (4.09)

23.8 (4.20)

30 (5.28)

25.6 (4.52)

26.8 (4.71)

27.5 (4.84)

35 (6.16)

28.7 (5.05)

30.1 (5.30)

31.0 (5.46)

40 (7.04)

31.5 (5.56)

33.2 (5.85)

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Table C.5: T100 Clip Effective Assembly R-Values for Alternative Vertical Clip Spacing Exterior Insulation Nominal RValue hr·ft2·oF/BTU (m2K/W) 16.8 (2.96)

Assembly Effective R-Value hr·ft2·oF/BTU (m2K/W) 27” Clip Spacing

34” Clip Spacing

41” Clip Spacing

48” Clip Spacing

55” Clip Spacing

15.5 (2.74)

16.4 (2.89)

16.9 (2.98)

17.3 (3.04)

17.3 (3.04)

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APPENDIX D – EXAMPLE SIMULATED TEMPERATURE DISTRIBUTION

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Figure D1: Temperature profile for T125 clip system with clips spaced vertically at 41 inches

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Figure D2: Temperature profile for T125 clip system with clips spaced 41 in o.c. and slab edge detail

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Figure D3: Temperature Distribution for the T125 clip system with interior insulation and clips vertically spaced at 41 inch.

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