Design Manual for Construction in Pakistan

DESIGN MANUAL REGIONAL BLOOD CENTERS PAKISTAN

Table of Contents Table of Figures ................................................................... 3 Abbreviations ....................................................................... 3 Preface ............................................................................... 4 Climate ............................................................................... 5 Urban Climate .................................................................... 7 Building in a Composite Climate .............................................. 8 Physiological Objectives ...................................................... 8 Design Criteria ................................................................... 8 Sun Orientation .................................................................. 9 Form and Planning .............................................................11 Building Zones ..................................................................11 External Spaces ................................................................12 Roofs and W alls ................................................................12 Surface Treatment .............................................................14 Ventilation and Air Flow ......................................................14 Building Envelope ................................................................15 Heat Flow .........................................................................15 Heat Transfer through the Building Envelope ..........................16 Absorptivity/ emissivity ....................................................17 Insulation Value ..............................................................17 Thermal Capacity ............................................................17 Terminology in Heat Transfer ...............................................17 Thermal Transmittance (U coefficient).................................17 Thermal Resistance (R) ....................................................18 Roof Design ......................................................................19 Thermal Insulation ...........................................................19 Radiative Protection ........................................................23 False Ceiling ..................................................................24 Construction Assembly .....................................................25 1

W all Design ......................................................................27 Construction Assembly .....................................................29 W indow Design .................................................................. 31 Conclusion..........................................................................32 Appendix A .........................................................................33 Selected Thermal Data Collection .........................................33 Overall Thermal Data Comparison ........................................35 Appendix B .........................................................................37 Roof Assembly ..................................................................37 References .........................................................................40

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Table of Figures 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

W orld Climate Map ........................................................... 5 High-Low Temperatures Islamabad ...................................... 6 Average Hourly Temperature .............................................. 6 Sun Hours of Islamabad .................................................... 6 Average Rainfall in Islamabad ............................................ 7 Islamabad Humidity Comfort Levels ..................................... 7 Islamabad Sun Path at Summer Solstice (June 21st) at Noon ..10 Islamabad Sun Path at W inter Solstice (Dec 21st) at Noon .....10 Zoning of House in Acoma Pueblo, New Mexico ....................11 - Thermal System of a Large Court-Yard House .....................13 - W hite vs. Bright Metal Surface .........................................14 - Insulation placement difference ........................................21 - Comparison between Roof Insulations ...............................22 - Comparison between Reflective Surfaces ...........................23 - Comparison between False Ceilings ..................................24 - Roof Assembly Detail .....................................................25 – Total Resistance and U Value of Assembly ........................26 - Cavity W all Configuration ................................................28 - W all Assembly...............................................................29 - Total Resistance and U Value of Assembly .........................30 - W indow Assembly ..........................................................31

Abbreviations

CDA – Capital Development Authority, Islamabad, Pakistan ENERCON – Pakistan Energy Conservation Center

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Preface This Design Manual is a synthesis of design methods recommended for creating sustainable buildings in Pakistan. It provides basic information on the impact of extreme climate and environmental conditions on a building and how the architect may mitigate these through design.

The most essential consideration in sustainable design is that of heat flow. The climate in Pak istan veers from extremely hot to humid to slightly cold, depending on the region and season. A deep understanding of the transference of heat through the building envelope will allow the architect to design more thermally sound buildings by using design and materials based on their thermal performance (such as brick, concrete, insulation, etc.).

This Manual will help the designer produce more energy-efficient buildings that will aid in reducing the building operational cost and contribute to the overall improvement of the energy situation in Pakistan.

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Climate Pakistan has two major climatic zones, Composite or Monsoon (e.g.

Islamabad, Lahore) and Hot-dry maritime desert climate (e.g. Karachi) (Konigsberger, T. and Mayhew 46).

1 - World Climate Map 1

In Composite or Monsoon Climate, two-thirds of the year is hot-dry.

The remaining one-third is warm-humid and cool-dry. During the monsoons, the rains are intense and prolonged, occasionally 25-38 mm within an hour. Annual rainfall varies from 500-1300 mm with 200-250 mm in the wettest month. Seasonal changes in relative humidity cause rapid weakening of building materials. Dust storms occur often and some occasional condensation problems arise.

1

(Compare Infobase Limited W orld Climate Map)

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2 - High-Low Temperatures Islamabad 2

3 - Average Hourly Temperature 3

4 - Sun Hours of Islamabad 4

2 3 4

(Weather Spark) (Weather Spark) (Weather Spark)

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5 - Average Rainfall in Islamabad 5

6 - Islamabad Humidity Comfort Levels 6

The Hot-dry maritime desert climate (such as Karachi’s) has two seasons, a hot one and a relatively cooler one. The day time maximum temperature is about 38 degrees and in the cool season it remains between 21 and 26 degrees. The moisture formed due to evaporation from solar radiation becomes suspended in the air (instead of precipitating), creating intensely uncomfortable conditions (Konigsberger, T. and Mayhew 46).

Urban Climate Urban area have different micro-climates. These factors depend on the following: •

5 6

Changed Surface qualities such as pavements and buildings that absorb solar radiation.

(Weather Spark) (Weather Spark)

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• •

Buildings that cast shadows and act as barriers for wind or by absorbing heat in their mass and slowly releasing it at night.

Energy Seepage through walls and ventilation of heated buildings and cooling units heat output.

Building in a Composite Climate Composite or monsoon climates, such as that found in Islamabad, are neither consistently dry, nor warm and humid. Their characteristics change from season to season, alternating between long hot, dry periods to shorter periods of concentrated rainfall and high humidity. Significant difference can be noted in the temperature, wind, rain, and sun conditions as shown in the graphs in figures 2, 3, 4, 5, and 6 .Since Islamabad is based at the foot of the Himalayan Mountain Range, it experiences a third season, with dry sunny days and uncomfortable cold nights, which is the winter season (Konigsberger, T. and Mayhew 245).

Physiological Objectives Physical comfort by day during the hot-dry seasons depend mainly on a reduction of the intense radiation from the sun, ground and surrounding buildings. To protect them a knowledge of periodic heat flow characteristics of various constructions will enable the designer to select walls and roofs which can, during the day, maintain inner surface temperatures less than the skin temperature (Konigsberger, T. and Mayhew 226).

At night the skin temperature is frequently low enough to permit an increase in effective temperature by surface temperature higher than this air temperature. Such an increase may even be beneficial (ENERCON and RCG/ Hagler, Bailly, Inc. 2-21). Breezes can be used to an advantage indoors, but only if the dust is filtered out.

Design Criteria As opposed to a hot-dry climate, which has a consistent climate through-out the year while only experiencing day/night temperature variations, the composite climate is difficult to design for due to the difference in the requirements of the three seasons. During the cold season, effective temperatures are much lower than in the two warmer 8

season, and physical comfort will depend on the prevention of heat loss from the mass, especially during the night. In the warm season, the heat dissipation is inadequate, so the designer attempts to increase it as much as possible. But this solution may not apply for the cold season, causing too much heat loss, making measures for the retention of heat necessary.

Thermal design criteria recommended for hot-dry climates are applicable not only in the hot-dry season of composite climates, but also in the cold season with the exception of minor details. For the monsoon or warm-humid climate, the solutions required are entirely different.

The middle ground, where conflicting climate design solutions are kept to a minimum while using solutions that apply to the composite climate as a whole effectively, a discomfort index is applied keeping the comfort temperature at 20 Degrees. The conclusion is that since the colddry and hot-dry seasons together dominate ten months while the humid season occurs only two months, the predominant seasons should be focused upon in the design criteria (Konigsberger, T. and Mayhew 247).

Sun Orientation As Pakistan is closer to the Equator, the altitude, therefore the angle of the sun relative to the horizon, is much higher. W ith an increased number of sun hours, this creates harsher living conditions outside during the hot-dry season.

The positioning of buildings in a tighter arrangement does not help when the sun is at its zenith in the summer as the shadows cast are short except in early morning and late afternoon.

W hen the sun is high, horizontal shading elements like roofs or tree canopies are extremely effective, especially in hot humid climates where buildings are placed further apart to encourage cross-ventilation.

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7 - Islamabad Sun Path at Summer Solstice (June 21st) at Noon 7

8 - Islamabad Sun Path at Winter Solstice (Dec 21st) at Noon 8

7 (Marsh, http://andrewmarsh.com/apps/releases/sunpath2d.html) (Marsh, http://andrewmarsh.com/apps/releases/sunpath3d.html) 8 (Marsh, http://andrewmarsh.com/apps/releases/sunpath2d.html) (Marsh, http://andrewmarsh.com/apps/releases/sunpath3d.html)

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Form and Planning In such climates, moderately dense low rise developments are suitable, which will ensure protection of outdoor spaces and courtyards, mutual shading of external walls, shelter from the wind in the cold seasons, shelter from dust and reduction of surfaces exposed to solar radiation. Shading of walls is desirable but not critical. Provided that the roof construction has a low transmittance value (U value) and good thermal capacity, there is little need for a double roof as is necessary in pure hot-dry climates. Thermal loading of roofs in hot-dry season is reduced by outgoing radiation to the open sky. External openings, however, do require shading during the hot and warm seasons.

Building Zones Buildings may be zoned according to their function and by the orientation of the sun. Rooms can be zoned so that activities can take place in cooler area during warm periods and warmer areas during cold periods of the day or season. The zones are graded from the most thermally controlled to least.

Design methods may also be used that simply moderate climatic extremes. They may take advantage of the beneficial relationship between some materials’ thermal characteristics and certain climate patterns, such as thermal time-lag and large diurnal temperature swings.

9 - Zoning of House in Acoma Pueblo, New Mexico 9

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(ENERCON and RCG/ Hagler, Bailly, Inc. 3-22)

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This house in Acoma Pueblo is an example of a two-zone residence and day-night design. One zone faces the terrace and is wind-protected and sunny during the day. An advantage when it is cool and a disadvantage when it is warm. It radiates heat to the sky at night, an advantage when it is warm, and a disadvantage when it is cool. The second zone, the interior room, follows the outside climate less closely than the terrace. The heat storage characteristics of the massive construction cause the interior temperatures to lag several hours behind the exterior temperatures. In the cool season the mass absorbs the sun’s heat during the day and releases it to the interior at night. In warm seasons, the mass is cooled at night by the air and by radiation to the sky, and so remains cool during the day (ENERCON and RCG/ Hagler, Bailly, Inc. 3-22).

External Spaces Projections help in reducing sun glare, keeping out rain and providing shade. These can include louvers and other sun breaks. These devices should preferably be of low thermal capacity.

Roofs and Walls In hot-dry season, due to the temperature variation between day and night, use of large thermal capacity structures is recommended.

These will absorb much of the heat entering through the outer surfaces during the day, before the inner surface temperatures will show any appreciable increase. To achieve this, walls and particularly roofs must be constructed of heavy materials, with a large thermal capacity. This will only work if the heat stored during the day is effectively dissipated during the night, before the heating process begins again. In climates where the night time temperature does not fall below comfort level, the large thermal capacity should be restricted to internal walls, partitions and floors, whilst the outer walls and roof would need to have a high resistive insulation (Konigsberger, T. and Mayhew 230).

The retention of night time low wall temperatures is desirable in the hot-dry season only, while the same thermal properties are useful in the cold season to retain the heat of the day for the uncomfortably cold nights. Roofs and external walls should, therefore, be constructed of solid masonry or concrete, to attain a 9-12 hour time lag in heat transmission. Higher thermal capacity, such as that of concrete, will be of

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a d v a n t a g e i n b o t h t h e h o t - d r y a n d c o l d - d r y s e a s o n s 10 ( K o n i g s b e r g e r , T . and Mayhew 248).

An intimate knowledge of thermal behavior of materials in necessary in order to select the most appropriate ones, or indeed the best sequence of layers for a composite wall/slab. For example, placing a light weight insulating material on the outside of a massive wall or roof will give a time-lag almost four times as much as if the same insulation is placed on the inside of the massive layer. At the same time the insulation placed on the outside will effectively prevent the heat dissipation to the outside air from the massive part during the night. Ample internal ventilation at night will thus become imperative, or else the buildup of heat over a few days will be unbearable.

Resistance insulation should be placed on the outside surface of external walls or roofs. Insulation on the inside would only reduce the beneficial effects of high thermal capacity walls and roofs.

An advantage of low-rise developments is the greater contact of walls with the ground, thus the ground will also be utilized for thermal storage (Konigsberger, T. and Mayhew 248).

1 0 - T h e r m a l S y s t e m o f a L a r g e C o u r t - Y a r d H o u s e 11

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In the warm-humid season a low thermal capacity but good insulated walls and roofs would be better, but the large thermal capacity would cause no great disadvantage. The best arrangement would be if the thermal capacity is provided in massive floors, partitions and ceilings, permitting the outer walls to be used more for large openings.

11 ( E N E R C O N a n d R C G / H a g l e r , B a i l l y , I n c . 2 - 2 3 )

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Surface Treatment The prevention of heat entering through the outer surfaces of the walls and roofs is a fundamental rule. Surfaces exposed to the sun during the hot and warm seasons should be light colored or of shiny polished metal.

The roof plays the most critical part in surface treatment. In this region solar radiation is almost as much as it will be near the equator.

And the roof is also the surface that will most readily emit heat by radiation to the sky. Thus this material selection of the roof will have a greater effect than that of walls. Bright metal and white paint have almost the same absorbance value of 0.1, but, as opposed to bright metal, white paint will have a greater emittance value of 0.8 (bright metal has 0.1).

Since we desire a higher emittance performance from the roof, the white paint will be the better choice.

1 1 - W h i t e v s . B r i g h t M e t a l S u r f a c e 12

Ventilation and Air Flow In hot arid regions, during the day-time openings should be closed and shaded. Ventilation should be kept to the absolute minimum necessary for hygienic reasons, to minimize the entry of hot and often dusty external air. Air intake openings should be located so that the

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(ENERCON and RCG/ Hagler, Bailly, Inc. 2-26)

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coolest and most dust-free air is take in. Thus the cool conditions existing at dawn can be maintained inside the building for the longest possible period.

In composite climate regions, the orientations of openings should be towards the breeze prevailing during the warm-humid season, to utilize its cooling effect. Openings towards the sun during the cold season helps in utilizing the heating effect or radiation entering through the windows.

Reasonably large openings on opposing walls can be opened for cross-ventilation during the warm-humid season and in the evenings in the hot-dry season (ENERCON and RCG/ Hagler, Bailly, Inc. 2-35)

Building Envelope Heat Flow The transference of heat and cold through the building envelope in a climate such as Pakistan’s is an important consideration in the design o f b u i l d i n g s . K n o w l e d g e o f t h e t h e r m a l d e c r e m e n t f a c t o r 13 a n d t h e r m a l t i m e - l a g 14 f o r d i f f e r e n t m a t e r i a l s , t h i c k n e s s e s , a n d c o m b i n a t i o n o f 13 T h e r m a l d e c r e m e n t f a c t o r i s i n v e r s e l y p r o p o r t i o n a l t o t h e r m a l l a g . I n other words, the higher the thermal lag, the lower the decrement factor. The reduction in cyclical temperature on the inside surface compared to the outside surface is known as thermal decrement. It is the attenuation of a wave traveling through an element of the building structure. For low thermal mass capacity building, the decrement factor will be 1.0 (100%). It will decrease as the thermal mass increases.

In the case of a 20 degree diurnal variation in external surface temperature, a material with a decrement factor of 0.5 would experiences only a 10 degree variation in internal surface temperature, which means only half the heat wave amplitude will pass through the wall (Marsh, http://performativedesign.com/guides/material-properties/ Thermal Decrement).

14 T h e r m a l l a g i s t h e t i m e d e l a y f o r h e a t t o b e c o n d u c t e d t h r o u g h a material. A material with high heat capacity and low conductivity will have a high thermal lag.

Thermal lag times are influenced by: *Temperature differentials between each face. * Exposure to air movement and air speed. *Texture and coatings of surfaces. *Thickness of material. *Conductivity of material. Thermal lag can be used to ease out internal/external diurnal temperature variations. In temperate climates, external wall materials with a minimum time lag of 10 to 12 hours can be very effective to reduce internal/external temperature variations during day and night. If it is required to keep the heat for a longer time, a layer of insulation can be added to slow the rate of heat transfer and

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materials in various constructional elements aids in this design. Heat gain should be permitted through the envelope only when there are heat losses by other channels such as ventilators. But this heat gain must be avoided when there is already a surplus of heat flow into the building.

Thus the selection of construction with an appropriate time-lag is an essential factor in the design (Konigsberger, T. and Mayhew 109).

T h e r m a l m a s s 15 i s a n o t h e r m a j o r f a c t o r . I t i s t h e p r o p e r t y o f a material that enables it to absorb, store, and emit heat energy. Materials with high density such as concrete, bricks etc. require a lot of heat energy to increase their temperature. They are therefore said to have high thermal mass. Lightweight materials such as timber have low thermal mass (Marsh, http://performativedesign.com/guides/materialproperties/ Thermal Mass). Low thermal capacity or ‘quick response’ structures (e.g. timber) warm up quickly but also cool rapidly. Large thermal capacity structures will have a longer ‘heat-up’ time and will also conserve heat once the heating is switched off (Konigsberger, T. and Mayhew 109).

Heat Transfer through the Building Envelope There is a continuous exchange of heat between a building and its outdoor environment. The factors affecting this transmission are convection (which depends on the rate of ventilation), radiation through windows, evaporation, and conduction, which may occur through walls and roof inwards or outwards.

The amount of heat penetrating the building depends largely on the nature of walls and roof. In the hot period of the day heat flows through these elements into the building where some of it is stored; at night, during the cool period, the flow is reversed. W hen appropriate materials are chosen it is possible to achieve and maintain comfortable internal temperatures over a wide range of external conditions.

moderate temperature differentials (Marsh, http://performativedesign.com/guides/material-properties/ Thermal Lag).

15 I t i s a l s o k n o w n a s t h e r m a l c a p a c i t a n c e o r h e a t c a p a c i t y . T h e r m a l mass acts as a heat sink. It absorbs heat from the environment and the interior space, keeping the house comfortable during the summer. The same thermal mass can release the heat at night, keeping the home warm during the winter.

When used well and combined with passive solar design, thermal mass can make a big difference in terms of comfort and energy use of a building by averaging day/night (diurnal) extremes. But Poor use of thermal mass can exacerbate the worst extremes of the climate and can be a huge energy and comfort liability (Marsh, http://performativedesign.com/guides/materialproperties/ Thermal Mass).

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The materials and type of construction need to be selected with the following characteristics in mind: absorptivity/ emissivity, insulation value, and thermal capacity.

Absorptivity/ emissivity Radiation from the sun striking an opaque surface may be absorbed or reflected. The color of the surface is a good indicator of its absorptivity for solar radiation, which decreases, with an increase in reflectivity, with a lighter color. The color of a material does not change its emissivity, or power to emit long-wave radiation at night.

Materials which reflect solar radiation rather than absorbing it will help prevent heat gain and help keep the temperatures lower within a structure.

Insulation Value As air is one of the best insulators, materials which enclose or contain air have low heat-transfer characteristics and generally are light in weight. The ability of a material to retard heat flow is known as thermal resistance, or it’s R-value. This is dependent upon the nature, density, and thickness of the material.

W alls, roofs and building components are often made up of two or more layers separated by air spaces which provide resistance to air flow.

The amount of this resistance depends not only on the width of the air spaces but also on the characteristics of the internal surfaces, as they are affected by the absorptive quality of the material surface (ENERCON and RCG/ Hagler, Bailly, Inc. 4-1).

Thermal Capacity Thermal capacity refers to the heat storage value of the material.

The larger this is, the slower the temperature change that is propagated through the material. This delay is called the thermal-time lag of the construction and materials with large time-lags are usually dense in quality and heavy in weight (ENERCON and RCG/ Hagler, Bailly, Inc. 42).

Terminology in Heat Transfer Thermal Transmittance (U coefficient) Total Thermal Transmittance is measured as the total heat gain that will occur across all of the environmental enclosures (e.g., walls, roofs, and floors) plus the amount of heat that will be gained as a result of 17

outside air infiltrating into the interior. To determine the thermal transmission that will occur across each enclosing element, it is first necessary to determine the rate at which transmission will occur. This transmission is referred to as the “U� coefficient. W hen we multiply it by the actual area of the appropriate enclosing element and the maximum expected temperature differential between the interior and the exterior, we get the heat loss contribution from that element.

It indicates the hourly rate of thermal energy transfer, per degree temperature differential, per unit of surface area of the thermal barrier.

These values help architects in designing an appropriate thermal barrier ( S m i t h 2 0 0 ) . 16 I n m o s t s i t u a t i o n s i t i s a s s u m e d t h a t t h e r e i s h e a t i n g a n d cooling in the respective seasons. As a result, even though there is a thermal transfer, the calculations presume that the thermal barrier continues to separate the inside ambient conditions from the outside ambient conditions. All exterior enclosing elements (walls, roofs), regardless of the particulars of their construction, separate the interior thermal conditions from the exterior thermal conditions. W ith this coefficient, we can calculate the difference in the rate of heat transfer between different wall and roof designs. The amount of transfer, as distinct from the rate of transfer, will also depend on the size of the barrier.

Thermal Resistance (R) Thermal Resistance (R value) is the ability of a material to retard heat flow (ENERCON and RCG/ Hagler, Bailly, Inc. 4-1). It is the conductance that occurs across an individual component of a construction assembly. It is the resistance of these individual c o m p o n e n t s t h a t i s a d d e d t o g e t T o t a l R e s i s t a n c e ( R T ) 17 w h i c h t h e n d e t e r m i n e s t h e o v e r a l l t r a n s m i t t a n c e . 18

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Thermal Transmittance is expressed as k cal/m2h deg C It is expressed as m2h deg C/k cal (MASCON Assoicates (PVT) LTD.

15) 18

If we measure the conductance through a unit thickness of a homogenous material, we would get the conductivity of the material.

Conductivity is the capacity of a material to conduct, as distinct from the specific quantity conducted. As the reciprocal of conductance is resistance, the reciprocal of conductivity is resistivity.

If we know the resistivity of a material, the resistance of a particular thickness of that material can be determined by multiplying the thickness by the resistivity per unit thickness (Smith 202).

Thermal Conductivity (k) of a material is the amount of heat that will flow through a unit area of material, of unit thickness in one hour, when the

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“U” and “R” values are inversely proportional (U=1/R). The lower the U value, the better the insulative quality; the higher the R value, the better the resistance to heat flow. R-values for individual materials, air spaces, air films, etc., are established. These are used to calculate the coefficient of the heat transfer for an entire building element, such as a wall. The R values of the individual materials are added together, then inverted to obtain the overall U value for the building element (ENERCON and RCG/ Hagler, Bailly, Inc. G-10).

Roof Design In the latitude of Pakistan, the roof typically represents 50 percent of the heat gain during the summer and 30 to 35 percent in winter. Most residential buildings in Pakistan are 1-2 storeys with flat roofs. W ithin cities, due to the closely placed structures, the roof becomes the most exposed part of the building (ENERCON and RCG/ Hagler, Bailly, Inc. 42).

In order to minimize the heat gains during the hot summer months it is important to reduce the surface temperatures of the roof. This can be achieved by: 1. Thermal insulation 2. Radiative protection 3. False Ceiling Thermal Insulation Flat Roofs W hen it comes to thermal insulation in Pakistan, flat roofs (or minimal slope roofs) may perform better than pitched roofs. They may have a tendency to leak- but only when poorly constructed and maintained. Flat roofs have better thermal performance because they often have a membrane system, which is applied on top of sheets of rigid insulation. Pitched roofs, on the other hand, commonly employ a cavity insulation system, where fiberglass batts- or loose insulation stuffed into insulation blankets-is pressed between the ceiling joists.

difference of two temperatures is maintained at 1 degree Celsius. It is expressed by k cal cm/m2h deg C (MASCON Assoicates (PVT) LTD. 15) Thermal Conductance (c) is the thermal transmission of a single layer structure per unit area divided by temperature difference between the hot and cold faces. It is expressed by k cal /m2h deg C (MASCON Assoicates (PVT) LTD. 15)

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Because the rigid insulation does not have gaps in it like the cavity system, it is more efficient. It is what building professionals refer to as “continuous” insulation. That means the roof has the same “R” value at every point, so there are no breaks in coverage (Modernize).

The type of insulation used in flat roofs differs greatly from pitched roofs. And in the Pakistani market, where flat roofs are used more often, the availability of this material is easier and the labor and skill more r e a d i l y a v a i l a b l e . 19 Since the surface area of the roof is significantly less in a flat roof as compared to a pitched roof, the amount of material needed significantly drops, decreasing the total cost of material and construction (High Tech Membrane Roofing Ltd.).

Effect of Insulation Roof insulation can considerably reduce the heat flux due to solar radiation incident on the roof as well as reduce heat loss to the outside in winter. The effect of the insulation on the indoor temperature will depend on whether the roof is made of light weight or heavy weight materials. Heavy-weight roofs have the ability to store the heat energ y to its capacity and then allow it to flow. By this process, the peak hour loads are delayed. For heavy-weight concrete construction, the insulation is applied on top of the slab, and must be protected from the sun and water penetration. In the case of light-weight or sloped roofing, the insulation is easily placed underneath the roof structure (ENERCON and RCG/ Hagler, Bailly, Inc. 4-3).

Position of Thermal Insulation T h e p o s i t i o n o f t h e r m a l i n s u l a t i o n 20 r e l a t i v e t o t h e h i g h t h e r m a l mass has a very significant effect on the time-lag and decrement factor.

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Pitched roofs are far better suited for areas with dramatic rise and fall of temperature. With pitched roofs, there is added insulation that a flat roof will not be able to keep at bay. Pitched Roofs also come with a hefty price tag as their design is complex and requires significant skilled labor and material, thus raising the cost. A flat roof is comparatively cheaper to construct (High Tech Membrane Roofing Ltd.).

20 M a t e r i a l s o r t h e m e t h o d s a n d p r o c e s s u s e d t o r e d u c e t h e r a t e o f h e a t transfer are referred as Thermal insulation. Heat energy can be transferred from a hotter object to a cooler object by conduction, convection and radiation. The flow of heat can be reduced by addressing one or more of these mechanisms and is dependent on the physical properties of the material employed to do this.

Insulation is used to minimize the transfer of heat energy. It acts as a barrier to heat flow and is essential to keep an enclosed area such as a building warm in winter and cool in summer. A well-insulated and welldesigned home will provide year-round comfort and can reduce energy use for

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The figure below shows the difference between placing a 40 mm (1.57 inches) glass wool insulation over or under a 100mm (3.93 inches) concrete slab.

1 2 - I n s u l a t i o n p l a c e m e n t d i f f e r e n c e 21

Insulation under the slab causes the heat to transfer from surface to surface in 3 hours, where 45% (or 0.45 decrement factor) of the heat wave amplitude will reach the inner surface. W hereas insulation over the slab, towards the exterior, will cause heat to transfer in 11.5 hours, where only 4.6% (0.046 decrement factor) of the heat wave amplitude will pass. Therefore, outside insulation in such climate will reduce the heat flow rate to the inner surface of the mass. Less heat will enter the mass in a given time and it will take longer to reach its thermal capacity.

Insulation on the inside will not affect the absorption process, but will reduce heat emission to the inside space.

In hot-arid climates, such as Pakistan’s, the aim must be to store the heat that the outer surface of the mass is exposed to during the day with least transference to the interior surface. During the night, this heat must be allowed to dissipate. If the insulation is towards the outside, the heat stored may only be dissipated effectively towards the inside, thus making it necessary to ventilate the interior surface with cool outside air (Konigsberger, T. and Mayhew 110). This may be achieved by choosing a material and construction with a high thermal mass, therefore a high thermal time-lag and consequently a low decrement factor. These values may be improved upon with the use of insulation, cavities, etc.

Types of Insulation A study conducted by the Capital Development Authority (CDA) in collaboration with UNHABITAT, ENERCON and the Ministry of Environment, demonstrates the “Improvement of Thermal Performance of RC Slab Roofs”. An area in Islamabad was selected with identical heating and cooling (Marsh, http://performativedesign.com/guides/materialproperties/ Thermal Insulation).

21 ( K o n i g s b e r g e r , T . a n d M a y h e w 1 0 9 )

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masonry houses with a 5 inch RC roof slab with leveling screed and bitumen waterproofing. These houses were each treated with a different thermal roof treatment and internal temperature variations recorded during 24 hours from May to August. One house was left untreated, called the “Control House” for a comparison between temperatures in treated and untreated residences. The following graphs compare information on only the most successful insulations. The numeric charts may be found in Appendix A along with the rest of the materials tested.

The following graph shows a comparison between the internal temperatures recorded in houses treated with the different above-slab insulation materials.

1 3 - C o m p a r i s o n b e t w e e n R o o f I n s u l a t i o n s 22

T h e c o n c l u s i o n w a s t h a t t h e e x t r u d e d p o l y s t y r e n e 23 g i v e s t h e l o w e s t internal temperatures as compared to the untreated “Control House”.

Details of the insulation types may be found in Appendix A.

22 G r a p h w a s m a d e u s i n g i n f o r m a t i o n f r o m s t u d y . V a l u e s f o u n d i n Appendix A. 23 J u m b o l o n b r a n d e x t r u d e d p o l y s t y r e n e i s u s e d . P o l y u r e t h a n e h a s similar resistive properties although is more flexible and water resistant.

22

Radiative Protection Flat or low-sloped roofs allow the creation of “cool roofs”, reflective or light-colored roof surfaces designed to direct heat away from building interiors by reflecting it back into the atmosphere. It would prevent rooftops from absorbing and transferring excess heat back inside, which would save on a building’s cooling demand. The flat nature of the roofs allow for the radiation to be reflected back into the atmosphere, whereas p i t c h e d r o o f s w i l l n o t d o s o a s e f f e c t i v e l y ( M o d e r n i z e ) . 24 Most of the heat transferred into a building is through radiation. A protective barrier for this type of heat is created with the use of highly reflective surface materials with low emissivity. These materials can be applied to the roof surface but their performance can seriously drop overtime as dust and the elements cause them to degrade, thus requiring a fresh coat.

The following graph shows a comparison between the internal temperatures recorded in houses treated with the different reflective materials.

1 4 - C o m p a r i s o n b e t w e e n R e f l e c t i v e S u r f a c e s 25

24 T h e d o w n s i d e i s t h a t t h e r a d i a t i o n r e f l e c t e d b a c k i n t o t h e a t m o s p h e r e raises the urban heat island index, therefore effecting the climate of the area.

25 G r a p h w a s m a d e u s i n g i n f o r m a t i o n f r o m s t u d y . V a l u e s f o u n d i n Appendix A.

23

The conclusion was that W hite Enamel paint gives the lowest internal temperatures. Details of the insulation types may be found in Appendix A. False Ceiling False ceilings act as insulation as they create a cavity between the roof slab and the false ceiling. This cavity acts as a barrier by reflecting the heat absorbed by the slab or by reflecting direct sun radiation. The cavity must be sufficiently wide and well ventilated to allow the heat to escape and not seep into the interior below.

The following graph shows a comparison between the internal temperatures recorded in houses treated with the different false ceilings.

1 5 - C o m p a r i s o n b e t w e e n F a l s e C e i l i n g s 26

The conclusion made is that a Paper Board false ceiling had the maximum impact on temperatures. The performance of the Thermopole false ceiling is similar, though slightly better than Gypsum Board false ceiling.

26 G r a p h w a s m a d e u s i n g i n f o r m a t i o n f r o m s t u d y . V a l u e s f o u n d i n Appendix A.

24

Construction Assembly A typical construction of an insulated roof in Pakistan would be with the use of polyurethane. In this application, the concrete roof is covered with a waterproof coating, the insulation is placed on top of this layer and then a final layer of crushed rock, or screed, is put down over the insulation to protect it from the ultraviolet rays of the sun. This insulation does not need to be protected from water as it allows very little water a b s o r p t i o n , a n d t h a t w a t e r d o e s n o t a f f e c t i t s i n s u l a t i v e p r o p e r t i e s . 27 A further addition of a tile or light concrete finish will allow for a reflective surface to be applied.

This roof has a thermal resistance eight times greater than the 6inch slab alone (excluding the effect of thermal mass storage). These types of roofs are more expensive to construct although they save considerable operational costs.

1 6 - R o o f A s s e m b l y D e t a i l 28

27 A n e a r l i e r d e s i g n u s e s e x t r u d e d p o l y s t y r e n e . I t i s t h e a d d i t i o n o f 2 inches of polystyrene on top of the 6 inch concrete slab, followed by waterproofing and a covering of light concrete. A disadvantage of this assembly is that the insulation is between the deck and the moisture resistant membrane. The insulation, being compressible, leads to the cracking of the membrane, which compromises the integrity of the water protection, affecting the performance of both the insulation and the roof as well (ENERCON and RCG/ Hagler, Bailly, Inc. 4-3).

28

Naqvi and Siddiquie Wall Detail

25

Assembly Components Total Resistance Thickness (mm)

Thickness (inch)

Roof Assembly Part

R Value (Imperial)

R Value (Metric) (SQ.m.·K/W)

(F°·SQ.FT.·HR/BTU)

Interior air film

0.12

1.1

False Ceiling

0.04

2.86

Air Space

1.72

1.84

15mm

5/8”

100600mm

12”-18”

150mm

6”

Concrete Slab

0.104

0.58

4mm

0.16”

Waterproofing (vapor barrier)

Negl.

0.06

50mm

2”

1.67

5.0

-

-

Polythene Sheet

Negl.

Negl.

70mm

2.75”

Leveling Screed (1:1.5:3)

0.042

0.2

Exterior Air film (reflective)

0.04

1.35

Total Resistance

3.736

12.99

“U” Coefficient

0.268

0.077

Polyurethane Insulation

17 – Total Resistance and U Value of Assembly

Temperature Drop across Barrier Interior temperature: 23 degrees Celsius Exterior Temperature: 45 degrees Celsius (above average)

Q=TA-TB / RT = Exterior Air film:

45-23/3.736 = t1=

5.89 45-(5.89x0.04) =

44.76 26

Leveling Screed:

t2=

44.76-(5.89x0.042) =

44.51

Polyurethane Insulation:

t3=

44.51-(5.89x1.67) =

34.67

Concrete Slab:

t4=

34.67-(5.89x0.104) =

34.06

Air Space:

t5=

34.06-(5.89x1.72) =

23.93

False Ceiling:

t6=

23.93-(5.89x0.04) =

23.69

Interior Air film:

t7=

23.69-(5.89x0.12) =

22.99/23.0

Wall Design Masonry W all construction is common practice in Pakistan. The masonry walls may be load-bearing, non-load-bearing, or simply panels between reinforced concrete frame structures. The masonry is mostly of solid burnt bricks and solid or hollow cement and sand concrete blocks, laid in cement and sand mortar. In some areas stone masonry is also used. W here the wall material is non-load-bearing, the use of light-weight concrete improves the thermal resistance.

Cavity Walls An unventilated cavity is a good insulator, equal to about a 7 inch brick wall. As it has been shown that the insulation should be outside of the main mass, it follows that the main mass should be located in the inner cavity of the cavity wall. The outer cavity should be of a light weight construction. The outer leaf should be constructed of hollow blocks or bricks, improving its thermal insulation but reducing its mass.

Tests have shown that ventilating the cavities during the day is undesirable, but night time ventilation of the cavity would assist in the cooling of the wall. Cavity walls are also effective in preventing the migration of moisture to the inside surface of the walls. The optimum dimension for the cavity air space is 2-3 inches.

If ventilated, the airflow during the day will be upwards within the cavity and downwards during the night. Both openings should be on the same side and should be closed during the day. If no provision is made for closing the ventilators then they should open towards the inside of the building, which itself must be adequately ventilated at night. As, however, an opening to the cavity would admit insects and vermin, it is better to have the cavity closed, unventilated (Konigsberger, T. and Mayhew 110).

27

1 8 - C a v i t y W a l l C o n f i g u r a t i o n 29

Wall insulation W all insulation can be installed either on the outer surface of the wall, on the inner surface, or inside the wall itself. In areas where cooling is predominant, the insulation should be placed over the outer most surface, and then covered with a protective layer. The most effective technique is to place the insulation on the inside surface of the cavity, thereby reducing the risk of moisture damage and improving the thermal resistance of the wall.

Wall Mass Effect The temperature rise in the building will depend on the mass of the wall and its heat storage capacity. Massive walls can store a large amount of heat at peak outside temperatures, releasing the heat at later, cooler, times of the day. Massive walls has been the traditional approach to temper the effects of wide fluctuations in temperature and to maintain interior comfort (ENERCON and RCG/ Hagler, Bailly, Inc. 4-7).

29

(Ching 5.24)

28

Construction Assembly A typical construction of a wall consists of a rigid board insulation between two masonry walls. The external brick layer is a facing brick while the internal is a thicker brick wall with a higher thermal mass.

19 - Wall Assembly

29

Assembly Components Total Resistance Thickness (mm)

Thickness (inch)

Wall Assembly Part

R Value (Metric) (SQ.m.·K/W)

R Value (Imperial) (F°·SQ.FT.·HR/BTU)

Interior air film

0.12

0.68

Plaster

0.06

0.2

Burnt Brick Wall

0.14

0.44

Negl.

0.06

Polyurethane Insulation

1.67

5.0

12mm

0.5

230mm

9”

4mm

0.16”

50mm

2”

115mm

4.5”

Burnt Brick Facing Wall

0.28

0.51

12mm

0.5”

Plaster

0.06

0.2

Exterior Air film

0.04

0.17

Total Resistance

2.37

7.26

“U” Coefficient

0.422

0.137

Waterproofing (vapor barrier)

20 - Total Resistance and U Value of Assembly

Temperature Drop across Barrier Interior temperature: 23 degrees Celsius Exterior Temperature: 45 degrees Celsius (above average)

Q=TA-TB / RT =

45-23/2.37 =

9.28

Exterior Air film:

t1=

45-(9.28x0.04) =

44.62

Plaster:

t2=

44.62-(9.28x0.06) =

44.06

Burnt Brick W all:

t3=

44.06-(9.28x0.28) =

41.46

30

Polyurethane Insulation:

t4=

41.46-(9.28x1.67) =

25.96

Burnt Brick W all:

t5=

25.96-(9.28x0.14) =

24.66

Plaster:

t6=

24.66-(9.28x0.06) =

24.11

Interior Air film:

t7=

24.11-(9.28x0.12) =

22.99 (23)

Window Design Solar radiation affects a building in two ways; not only is it absorbed by the opaque walls and roof structures, but it also enters through glazed areas, which transmit solar (short-wave) radiation with very little loss in energy. Glass has the property of allowing the shortwave radiation to pass through but not the long-wave radiation emitted by objects or surfaces in the room. Thus heat that enters as sunlight through the glazing materials is trapped and can increase the indoor temperature to far above to that of the air outdoors. The use of glass in hot climates requires careful attention to size and placement of materials, as well as the design of interior and exterior shading devices.

21 - Window Assembly

The most commonly used windows are double-glazed. The above assembly is a 24mm double glazing assembly that provides us with a Ucoefficient of 1.78 (W /m2.K) in summer.

31

Conclusion

It is very important to work with the climate in a country like Pakistan, rather than attempting to insulate the building completely against the outside environment. The building must be designed by understanding the transference of heat into and out of the envelope.

Methods must be employed to take any excess heat away strategically.

The use of materials with a high thermal mass, such as concrete, is not detrimental to a building design in Pakistan, but rather advantageous if used appropriately while keeping the thermal heat transference in mind.

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Appendix A Selected Thermal Data Collection

30

30 ( U N H A B I T A T ; E N E R C O N ; M i n i s t r y o f E n v i r o n m e n t ; C a p i t a l Development Authority (CDA); 17)

33

34

Overall Thermal Data Comparison

31

31 ( U N H A B I T A T ; E N E R C O N ; M i n i s t r y o f E n v i r o n m e n t ; C a p i t a l Development Authority (CDA); 65-66)

35

36

Appendix B Roof Assembly

R o o f A s s e m b l y T y p e f r o m D e s i g n M a n u a l 32

32

(ENERCON and RCG/ Hagler, Bailly, Inc. 4-56)

37

R o o f A s s e m b l y T y p e f r o m D e s i g n M a n u a l 33

33

(ENERCON and RCG/ Hagler, Bailly, Inc. 4-58)

38

R o o f A s s e m b l y f r o m N H B C 34

34

National House Building Council standards Document, UK (NHBC)

39

References Ching, Francis D. K. Building Construction Illustrated Fourth Edition. New Jersey: John W iley & Sons, Inc., 2008.

Compare Infobase Limited. https://www.mapsofindia.com/worldmap/climate.html. 2017. Google Chrome. 29 August 2017.

ENERCON and RCG/ Hagler, Bailly, Inc. Design Manual for Energy Efficient Buildings in Pakistan. Islamabad: The National Energy Conservation Center, 1990.

High Tech Membrane Roofing Ltd. http://www.hightechmembraneroofing.co.uk/blog/what-areadvantages-flat-roof-compared-pitched-roof. 2015. Article. 09 September 2017.

Holiday W eather Limited. http://www.holidayweather.com/islamabad/averages/. 2017. 30 August 2017.

International Masonry Institute. http://imiweb.org/masonry-detailingseries/. n.d. Google Chrome. 5 September 2017.

Konigsberger, Otto H., et al. Manual of Tropical Housing and Building: Climate Design. Hyderabad: Universities Press, 2011.

Marsh, Dr. Andrew J. http://andrewmarsh.com/apps/releases/sunpath2d.html. 2014.

Google Chrome. 7 September 2017. —. http://andrewmarsh.com/apps/releases/sunpath3d.html. 2014. Google Chrome. 7 September 2017. —. http://performativedesign.com/guides/material-properties/. 9 November 2010. Google Chrome. 29 August 2017.

MASCON Assoicates (PVT) LTD. Conduct of Building Energy Audit in ENERCON Building Islamabad. Final Draft Report. Islamabad: ENERCON , 2011. Report Document.

Moder nize. https://moder nize. com/ home- ideas/34127/f lat-r oof-mor eenergy-efficient. 2017. Google Chrome. 09 September 2017.

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NHBC. http://www.nhbc.co.uk/Builders/ProductsandServices/Standardsplus 2017/#294. n.d. Website. 09 September 2017.

Smith, David Lee. Environmental Issues for Architecture. New Jersey: John W iley & Sons, Inc., 2011. Book.

Solomon, J.K. https://www.newlearn.info/packages/clear/thermal/buildings/building_fabric/properti es/time_lag.html. 2002. Google Chrome. 29 August 2017.

UNHABITAT; ENERCON; Ministry of Environment; Capital Development Authority (CDA);. Energy Efficient Housing - Improvement of Thermal Performance of RC Slab Roofs. Research Report.

Islamabad: ENERCON, 2010. Document.

W eather Spark. https://weatherspark.com/y/107761/Average-Weather-inIslamabad-Pakistan-Year-Round. n.d. Google Chrome. 5 September 2017.

W ind Finder. https://www.windfinder.com/windstatistics/islamabad_rawalpindi_air port. n.d. 30 August 2017.

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