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Introduction

Adelaide HomesDesign Guide 5 - Materials

1. Insulation

cold internal space warm internal space

Reflective insulations

Properly chosen structural and insulating materials will improve comfort and make your home moreenergy-efficient.

In Adelaide's climate, building materials must respond adequately to both hot summer and cold winterconditions.

Choosing proper materials is a crucial stepin planning and designing your home.Besides such important considerations asdurability, cost, buildability and fireresistance, there are two performancemeasures that will affect your homecomfort: its ability to accumulate heat, andits ability to insulate against heat loss.

In the Adelaide climate, a home shouldprovide protection from heat duringsummer and from cold during winter. Oneset of building materials is expected toserve both these functions. When defininginternal comfort, we will talk aboutinsulation and thermal mass.

Insulation materials have high resistance toheat flow (high R-values). The higher theR-value, the higher the level of insulation.There are two main categories of insulationproducts: bulk and reflective.

Insulation is a barrier to heat flow. Itprevents internal heat from leaving thehome when outside temperatures are low,and external heat from entering the homewhen outside temperatures are high, thusalso keeping the home cooler duringsummer.

Reflective insulation has an air layer next tothe reflective surface and it mainly resistsradiant heat. Reflective insulation can have'up' or 'down' R-values, depending whetherit resists heat flow upwards or downwards.It usually consists of shiny aluminium foillaminated onto paper or plastic.

in summer in winter

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Bulk insulations

roll of foil

RFLs have the greatest effect when installedunder the roof construction. This way, theyare able to reflect almost 95% of infraredrays preventing them from penetrating theroof and heating up the space below. RFLscan also be installed on the top of a ceiling,but this won't stop overheating of roofspaces and the heat will enter the home byconduction.

Reflective foil laminates (RFLs)

home with different sections at differenttemperatures

Bulk insulation has pockets of air trappedwithin its structure and it resists conductionof heat in any direction. Bulk insulationmaterials include glass, mineral and rockwool, polyester, and polystyrene.

wool insulation

Wool insulation made from sheep's woolfibers is a natural material that does notendanger people's health or environment. Itcan absorb and release moisture withoutdecreasing its thermal insulation properties.

Glass wool is made of molten minerals:glass or rock. Glass wool is resistant to fireand insects, has good acoustic qualities, andis the cheapest insulation product, but itmust be handled with caution as it canirritate the skin. In addition, it loses itsinsulating abilities if it becomes wet. Rockwool or stone wool has stronger acousticand fire-resistant properties than glasswool, and also irritates the skin duringinstallation. Rock wool has advantageswhen fire resistance requirements are high.

Expanded polystyrene (EPS) insulation is themost common polystyrene insulation. It hashigh compressive strength and is water, rotand vermin resistant. However, it reduces insize over time, creating gaps or thermalbridges between installed pieces.

Extruded polystyrene (XPS) insulation isstronger than EPS and is suitable for usebelow ground or where an extra load isexpected. It doesn't change its size over itslifespan.

Polyisocyanurate foam (PIR) is an improvedversion of polyurethane (PUR), anothercommon insulation material. PIR has goodinsulation and compression values, but itshrinks in size across its lifetime.

According to the Building Code of Australia(BCA), the climate in Adelaide requires aminimum insulation level (total R-value) of4.1 for roofs and ceilings, and 2.8 for walls.

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2. Thermal Masses

day day

nightnight

Externalthermal mass

Internalthermal mass

Well-insulated and sealed homes must dealwith an increase in the level of moistureinside. Water vapor moves through theconstruction and condenses when the airreaches the dew point. This can have anegative effect on materials that loseperformance when wet. There are vaporbarriers on the market which restrict thetransmission of water vapor, andvapor-permeable (breathable) membranesthat allow vapor to pass through.

In the temperate climate of Adelaide, watervapor movement can be both from inside tooutside and vice versa. External membranesshould be breathable, and those insideshould prevent vapor entry.

A thermal mass is any material with thecapacity to accumulate heat and release itwhen the heat source is no longer available.As it is not an insulating material, wheninstalled as an external wall it must beinsulated on both the exterior side andinterior sides.

Incorporation of a thermal mass into thehome should be planned together withother passive heating and cooling systems.It gives the best performance if dailytemperature ranges are greater than 6°C.

Thermal mass can be brick, stone, concreteblock, concrete wall or slab, clay roof tile,rammed earth wall, or liquid (water orphase-change materials) packed intocontainers.

A thermal mass serves both for passiveheating and cooling, but its use has to beplanned carefully. During hot summer days,well-insulated external walls and concreteslabs on the ground will remain cool for along period, keeping internal temperatureslower than outside.

Heat accumulated during the day is thenreleased during the night. In this scenario,these elements must be exposed to coolingnight-time air.

During the cold winter days, thermalmasses will accumulate heat only whenexposed to direct sun or additional heatsources (e.g. heat banks or floor heating).External walls will lose their heat towardthe outside, but internal thermal masseswill heat the internal spaces. If there is alarge surface area of north-facing windowsthe home can be overheated, even duringwinter. Internal thermal mass will help todrain excessive heat.

external and internal thermal masses beingwarmed

Guidelines for designing a thermal mass saythat: the portion of its surface area exposedto the sunlight coming through thenorth-facing windows should be 3 to 6times the area of those windows themselves

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3. Floors

solid brick

bulk insulation

mortar

in order to prevent a concentratedoverheating of one small part of the thermalmass; they should be darkly colored toallow better absorption; and they shouldnot covered (e.g. by carpets).

Floors can be either lightweight orhigh-mass. Lightweight floors areconstructed around timber or steel framing.While a timber construction is subject totermites, a steel frame can suffer corrosion.

High thermal mass floors are concrete slabs,either laid on the ground or suspended.Slabs on ground are coupled with earth,which maintains a constant temperature ofbetween 16°C and 19°C. Slabs can be ofconventional or waffle pod design. Wafflepod slabs consist of a grid of insulation(expanded polystyrene) and concretebeams.

Mass floors should be exposed to the sun inwinter but covered during summer days.They should also be exposed to the night'scooling air, especially if they are on upperstories where warm air accumulates.

In order to have a passive heating effect,floor slabs should be covered with finishesthat will not prevent heat absorption, likeceramic or terracotta tiles. Floors coveredby carpets will be insulated and preventheat accumulation.

Additionally, the thermal mass of concreteslabs can be heated by hydronic floorheating systems.

Brick can either be laid down in two leavesseparated by a cavity that reduces moistureand heat transfer, or as solid brick orblockwork that has a high thermal andload-bearing capacity. Brick, if not painted,requires little or no maintenance andpossesses high durability. Concrete bricksare more porous and must be sealed toprevent water penetration.

composition of a high-mass wall

Concrete block is larger than brick and hashollows that can be filled with insulation.Autoclaved aerated concrete blocks aremuch lighter with a higher thermalresistance, but they have a lower structuralcapacity.

Both clay and concrete are fire- andvermin-resistant.

Light-frame walls consist of timber or steelframing as structural support for claddingand linings. They are well-insulatedbetween frame elements. The appearanceof lightweight walls depends on the type ofcladding. It can be corrugated steelsheeting, fiber cement sheets, timberweatherboard or plywood sheets.4. Walls

High-mass walls are masonry wallsconsisting of either brick, stone, concreteblock or concrete. These walls have externalinsulation and strong footings.

Plasterboard or magnesium oxide board iscommonly used for inside linings. As all ofthese materials have no influence on

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Additional wall-building materials

brick veneerairspacereflective foil

timber

bulk insulationreflective insulationfibre cement

insulation, they should be chosen on thebasis of other performance measures, suchas breathability and waterproofness,maintenance requirements and durability,aesthetics, and fire resistance.

composition of a light-frame wall

carefully. Its beauty is usednowadays more asdecoration in internal wallsand around fireplaces.

Stone masonry has a long tradition but it requires askillful builder. Stone is also a heavy material that needssubstantial support. It has low thermal resistance andtherefore needs to be insu-lated, and high thermal mass,so its use should be planned

stone wall and steps

Glass block possesses some of the properties of bothmasonry and glazing. It is made of two halves ofheatproof glass pressed together tocreate a cavity filled with air. It hasa higher thermal insulation valuethan double-glazing. Glass blocksset in mortar form self- supportingwalls, but generally they are set in aframe made of steel or aluminium.

glass block wall

Straw bales can be stacked in timber frames. They haveno thermal mass as they contain mostly air, but haveexcellent insulating performance. Indeed, they are themost cost-effective of all thermal insulators currentlyavailable.

The only thermal mass applied tolight-frame walls are reverse brick veneersplaced on the internal side, where they areinsulated from the wall but exposed tointernal heat.

Timber and steel are both commonmaterials for framework, so it is worthsummarizing the main differences betweenthe two. Termites are the major concern intimber construction but, compared to steelframes, timber has longer stability in fire,can hold suspended furniture, and containssmall (or no) thermal bridges. Steel is anefficient conductor of heat and thereforesteel frames have to be insulated externally.Both timber and steel can be damaged by along exposure to wet conditions.

Cob is a mixture of earth, sand, gravel and straw withwater. It is usually mixed and applied by hand, allowing

sculptural forms of walls.Cob needs protection fromheavy weather conditions(it should be whitewashedwith lime and water).

cob wall

Rammed earth is a material made by ramming togethera mixture of gravel, sand, silt and a small amount of clay.Walls are usually 300mm thick and can bear the load of

several floors. Rammedearth has high thermalmass, but low insulatingproperties. It also needs tobe protected fromexposure to moisture.

rammed earth wall

Mud brick is made by mixing earth with water anddrying in molds in the open air. Straw, which is strong intension, is added in order to reduce cracking. Mud bricksare held together with mud mortar. To provide effectivethermal mass, the walls should be a minimum of 300mmthick and properly insulated, as dried earth is not a goodinsulator. Mud brick needs protection from severeweather.

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5. Roofs 6. Glazing

As an internal lining, magnesium oxideboard is likely to replace gypsum board orplaster board. It has strength and resistancedue to very strong bonds between themagnesium and oxygen atoms that formthe magnesium oxide molecules. Theseboards are non-toxic, have a high fire- andvermin-resistance, are very durable andmaintain dimensional stability even whenwet. Having a strong bonding surface, theycan be finished in many ways. As they arealso water-resistant, they can be installed asexterior finishes.

Roofs are the home surfaces most likely tobe exposed to the sun all day long,especially during summer when the sun ishigh in the sky. The roof should beintensively insulated rather than beingconsidered a thermal mass. A roof is also asuitable place for installing solar collectors.

green roof

Roofs are usually insulated on the inside ofthe construction, but roofs designed to actas a thermal mass can be insulatedexternally and exposed internally. In anearth-covered construction, a thick layer ofearth with a garden provides a significantbarrier to heat loss, allowing the internalmass construction to accumulate heat fromthe inside. Green roofs, being covered withlightweight manufactured material, cannotprovide sufficient thermal insulation.

To avoid becoming overheated, roof covershould be light-colored to reflect the mostof the sun's rays. Dark colors or clay tilesaccumulate heat and transfer it to thehome. Tiles absorb heat as any otherthermal mass and release it in all directionswith a delay during the night, when thehome actually needs cooling. Clay tiles alsorequire more structural support than otherroofing materials.

Metal roofs are often accused of being noisyin the rain. This noise is largely reducedthrough the use of insulated blanketsarking.

Glazing plays an important role in passiveheating. Glazing should allow as much heatfrom the sun as possible to penetrate intothe home during winter, but prevent thesame heat from leaving the home when thesun sets. There are two values that describethe performance of the windows whichmust be considered when choosing theproper glazing.

Solar heat gain coefficient (SHGC) measureshow much heat from direct sunlight canflow through a window, and is expressed invalues from 0 to 1. Higher values describegreater heat flow, and thus greater heatgain. In Adelaide's climate, northern-facingwindows should have the highest possibleSHGC value.

Conduction (or U-value) measures howmuch heat a window conducts; in otherwords, how much heat is lost to the coldoutside environment. The lower theU-value, the greater the resistance to heatconduction, meaning better insulatingcapability.

There are many glazing products on themarket, but two have been shown to be themost energy-efficient.

Double-glazed windows

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ArchitecturalEnergy Efficient Homeswww.endurobuilders.com.au

Low-E glass

7. Recommendations for

outside inside

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double glazedwindow withlow-e coating

building in Adelaide

Double-glazed windows consist of two glasspanes separated by a layer of still air or gas,combined in one frame. The sealed air gap,which should be a minimum of 12mm wide,acts as an insulator. The internal pane thenremains as warm as the interior space andcontributes to overall comfort.Double-glazing also reduces condensation.For higher insulating values, the gapbetween glass panes can be filled withnatural gases such as argon, which has lowconductivity properties. Double-glazedwindows are still not resistant to directsunlight, so they need proper shadingduring summer days.

Low-E refers to low emissivity; the capacityof a surface to radiate heat. It is expressedin a range from 0 to 1, where 1 representsthe highest emissivity.

Low-E glass is a standard clear glass panecovered with a special coating on onesurface. Low-E glass reduces the amount ofheat conducted by almost 30% compared toordinary glass. The best solution can befound in the combination of low-E glass anddouble-glazing. This, with a suitable frame,can stop up to 70% of the heat lossexperienced with a single clear 3mm glasspane.

In single-pane windows, a low-E coatingshould be placed on the internal side. Indouble-glazing, the best position willdepend on your main priority.

double-glazed window composition

If the priority is insulation, then the coatingshould be applied to the external surface ofthe inside pane (surface number 3). Thecoated pane will absorb any heat beforeescaping and radiate it back into the room.

* Choose lightweight construction forexternal walls and the proper amount ofthermal mass for floors and walls inside.Earth coupled slabs are recommended.

* Use both reflective and bulk insulations inceilings, roofs and walls. Insulateslab-on-ground edges and slab undersides ifusing floor heating. All thermal masses mustbe insulated on the external side. Ceilingsshould have R4.1 batts, roof R1.3 blanketand walls R2.5 insulation level. The roofshould be covered with light-colored metal.

* Walls facing east, south and west shouldhave reverse veneers with anti-glare foil,while walls facing north just require lightlinings.

* Seal windows, sliding doors and hingedexternal doors with weather strips. Sealexhaust fans, kitchen range hoods and allplaces of heat leakage.

* Use double glazed windows with low-Ecoatings.

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If it is more important to reduce summerheat gain, then the coating should beapplied to the inside surface of the externalpane (surface number 2). The coating willabsorb incoming heat and radiate it back tothe outside.