THERMAL BRIDGING AND SAP 10
In the ever-evolving landscape of building regulations and energy efficiency standards, we at Buildpass keep a close eye on the guidance that shape how the construction industry works. A crucial turning point occurred when SAP 10 was introduced, representing a substantial revision that fundamentally altered our approach to addressing thermal bridging in building design. In this guide, we’ll dive into the impact of SAP 10 on thermal bridging calculations and explore what it means for your construction projects. SAP 10 brought about substantial changes in how thermal bridging is calculated and addressed in building design. While the details can be complex, we’ll break it down into easy-to-understand terms. Thermal bridging, in essence, refers to the areas in a building where heat can escape more readily than in the surrounding areas.
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How has SAP 10 changed thermal bridging calculation guidelines? To make sure building developments are as sustainable as possible, environmental factors – such as the 7 principles of sustainable construction – must be considered from the very earliest stages of the building establishment. These sustainable movements have become more and more prevalent since the release of the Climate Change Act (2013), the UK Government’s 2025 strategy, which set a target of 50% reduction in greenhouse gas emissions in the built environment by 2025. So, what are the 7 principles of sustainable construction you may ask? The 7 principles of sustainable construction is a method for contributing to a greener built environment while reducing our overall carbon footprint.
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Sustainable Design
Durability
Energy efficiency
Waste reduction
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Indoor air quality
Water conservation
Sustainable building
What does this mean for my project? First and foremost, complying with SAP 10 guidelines is essential for meeting building regulations and obtaining necessary approvals. Failing to address thermal bridging adequately can result in a building that doesn’t meet the required energy efficiency standards, potentially leading to costly redesigns or delays. Designers and builders will be encouraged to calculate the actual junctions and thermal bridging details in your specific building rather than relying on standard Ψ-values. This change helps ensure buildings are more energy-efficient and better at keeping heat inside. Furthermore, SAP 10 encourages a more holistic approach to building design. It highlights the importance of considering thermal bridging from the outset, rather than as an afterthought. This shift in mindset can lead to more efficient, environmentally friendly, and cost-effective buildings.
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A Psi-value (also written as a ψ–value) is the measure of how much heat is expected to be lost through a particular junction measured in Watts per metre Kelvin (W/mK).
What are my options? When it comes to addressing thermal bridging in your projects under SAP 10, you have several options at your disposal. These options can be tailored to your specific project requirements and budget constraints. One approach is to invest in high-performance insulation materials and construction techniques. By using materials with low thermal conductivity and optimising insulation placement, you can significantly reduce thermal bridging and improve energy efficiency. There are a number of manufacturers whom have calculated thermal bridging values for their products which cover common constructions details, these include: •
Knauf
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BRE
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Building Alliance Recognised Construction Details
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Hanson / Aircrete Block
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Republic Of Ireland Acceptable Construction Details
Another option is to utilise advanced thermal analysis software. These tools can simulate and predict heat loss through different building components, allowing you to identify potential thermal bridging issues and make informed design decisions.
What about Passivhaus? A thermal bridge ‘free’ design is one of the 5 fundamental principles of Passivhaus design and construction. For the Passivhaus Standard, thermal bridge free construction is where calculating the heat loss from all the thermal bridges doesn’t increase the overall building heat loss calculation. If thermal continuity has been considered from the outset, it is possible to achieve thermal bridge free construction. If it hasn’t been considered, or other factors influence the design, then each thermal bridge needs close consideration. Some can be easily minimised or eliminated through careful detailing.
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What should we be targeting?
Ref
Junction detail
Default Y (W/m.k)
Target Y (W/m.k)
Junctions with an external wall E1
Steel lintel with perforated steel base plate
1.00
0.05
E2
Other lintels (including other steel lintels)
1.00
0.05
E3
Sill
0.10
0.05
E4
Jamb
0.10
0.05
E5
Ground floor (normal)
0.32
0.16
E19
Ground floor (inverted)
0.10
0.07
E20
Exposed floor (normal)
0.32
0.32
One particularly useful resource is a graph that visually represents the heat loss from various building components. By referencing this graph, you can pinpoint the areas with the highest thermal bridging risk and prioritise improvements accordingly.
E21
Exposed floor (inverted)
0.32
0.32
E22
Basement floor
0.22
0.07
E6
Intermediate floor within a dwelling
0.14
0.00
E7
Party floor between dwellings (in blocks of flats)
0.28
0.07
E8
Balcony within a dwelling wall insulation continuous *
0.10
0.00
E9
Balcony between dwellings wall insulation continuous *
0.15
0.02
E23
Balcony within or between dwellings balcony support penetrates wall insulation
1.00
0.02
E10
Eaves (insulation at ceiling level)
0.12
0.06
E24
Eaves (insulation at ceiling level - inverted)
0.15
0.24
This table shows the values used if you do not calculate the specific thermal bridging detail or use a pre-calculated detail from one of the approved sources listed above. The second value shows the targeted psi value, which is used to create the Building Regulations targets.
E11
Eaves (insulation at rafter level)
0.15
0.04
E12
Gable (insulation at ceiling level)
0.25
0.06
E13
Gable (insulation at rafter level)
0.25
0.08
E14
Flat roof
0.16
0.08
E15
Flat roof with parapet
0.30
0.56
To determine where you should focus your efforts in mitigating thermal bridging, consider consulting the SAP 10 guidelines and associated documents.
E16
Corner (normal)
0.18
0.09
E17
Corner (inverted – internal area greater than external area)
0.00
-0.09
E18
Party wall between dwellings
0.24
0.06
E25
Staggered party wall between dwellings
0.24
0.06
Junctions with a party wall P1
Ground floor
0.32
0.08
P6
P6 Ground floor (inverted)
0.32
0.07
P2
Intermediate floor within a dwelling
0.00
0.00
P3
Intermediate floor between dwellings (in blocks of flats)
0.00
0.00
P7
Exposed floor (normal)
0.48
0.16
P8
Exposed floor (inverted)
0.48
0.24
P4
Roof (insulation at ceiling level)
0.48
0.12
P5
Roof (insulation at rafter level)
0.40
0.08
Junctions within a roof or with a room-in roof R1
Head of roof window
0.24
0.08
R2
Sill of roof window
0.24
0.06
R3
Jamb of roof window
0.24
0.08
* This is an externally supported balcony (the balcony slab is not a continuation of the floor slab) where the wall insulation is continuous and not bridged by the balcony slab or its supports
R4
Ridge (vaulted ceiling)
0.12
0.08
R5
Ridge (inverted)
0.12
0.04
R6
Flat ceiling
0.12
0.06
** For rooflights installed on third party upstands or builder’s kerbs there will be additional thermal bridges between the upstand or builder’s kerb and the rooflight; refer to BR443 (2019) for further details.
R7
Flat ceiling (inverted)
0.12
0.04
R8
Roof to wall (rafter)
0.12
0.06
R9
Roof to wall (flat ceiling)
0.32
0.04
R10
All other roof or room-in-roof junctions
0.32
0.08
R11
Upstands or kerbs of rooflights**
0.24
0.08
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