Concertina FOIL BATTS - Thermal and Breathing Performance

www.concertinafoilbatts.com www.afia.com.au Aluminium Foil Insulation Assoc. Nov, 2003

Note: Alterations to R values pending

HEAT TRANSFER and HOME INSULATION

There are three methods by which heat flows –

i) radiation - the emission of heat waves passing through air or a vacuum

ii) conduction - contact from one body to another

iii) convection - upward movement of warm air

Radiation is the first and predominant form of heat transfer. In winter, heat is lost through ceilings, walls and windows by radiation followed by convection, whereas framed timber floors lose heat only by radiation downwards – there is no convected heat loss. Heat gain in summer through ceilings, walls and windows is entirely by radiation, not convection.

Federal and State building energy efficiency regulations exist to reduce energy used for artificial heating and cooling, in order to reduce national greenhouse gas emissions.

Heat flow in and out of buildings in Australia is influenced by many factors.

· Identifying the climate and the dominant direction of heat flow – in or out or mix of both.

· Temperature difference between indoor and out. Outdoor ambient shade temperature versus direct radiation entering buildings through ceilings, walls and glazing. How to stop radiation penetration.

· Amount, type and cost of heating and cooling needed to maintain desired human comfort levels.

· Building design and orientation to the sun, mass versus lightweight construction.

· Advantages of Open versus Closed building design in hot climates.

Open design homes are energy efficient and healthy using cool air by natural ventilation, assisted by ceiling fans or evaporative appliances. Most effective cooling time is in the evening.

Closed design requires cold refrigerative air to be produced in order to maintain an artificial internal temperature. It is the most expensive form of cooling and is unhealthy.

· Thermal performance of all building materials (including insulation) against heat flow in or out. Expressed as Rvalues – the higher the R, the greater the resistance. The ‘material’ Rvalue is different to the installed or ‘total’ Rvalue – eg R2.5 fibre batts in ceilings is not continuous R2.5 because of bridging effects and produces Total R2.2 for timber joists and lower again for steel.

· Insulation levels and the Law of Diminishing Returns. Initial insulation makes the most significant effect and increasing levels beyond R2.0 in ceilings has rapidly diminishing economic and comfort benefits – twice the Rvalue does not give a doubling in energy savings for heating or cooling. It is better to consider all of the heat paths in a particular building rather than to insulate one of them heavily – this is called the overall principle of insulating.

· Determining the most appropriate and effective insulation for varying Australian climates.

Insulation materials are considered the single biggest factor affecting the resistance capabilities of the building envelope and there are generally two types of insulation: bulk and reflective.

i) Bulk insulation works by means of small air pockets which retard or restrict the flow of heat - and have “material Rvalues”. Resistance is always measured under steady-state conditions, commonly in a Heat Flow Meter, where the material is placed between two metal plates set at fixed unchanging temperatures of 33 and 13degC, where the mean or average temperature is 23deg and the testing duration is 4 hours.

Bulk insulations originate from the northern hemisphere (about 60 years ago) to keep heat inside buildings and are not tested against high temperature radiation entering buildings through roofs/ceilings and walls, as what occurs across the entire Australian continent, where the underside of metal roofs have recorded downward radiating temperatures of approximately 80-100degC.

ii) Reflective insulation reduces the flow of heat by reflecting radiation away on the warm side and giving off very little on the cool side. Aluminum foil insulation, with airspaces, will provide a continuous and permanent resistance to the flow of radiation – by 97% reflectivity on the side of the heat source and 3% emissivity, or re-radiation, from the opposite surface. Foil insulations do not have material Rvalues and are expressed as “Total Rvalues”, being the sum of the entire wall or ceiling/roof structure, including the resistance values of foil airpaces from calculation tables and computer programs, derived from physical testing in the USA 1950’s of variable width parallel foil airspaces.

FOIL INSULATION

Why does it work? Aluminium foil insulation works on similar principles of the thermos flask - rings of aluminum, kept apart and not touching. Trapped still airspaces are good forms of insulation - dramatically better if the spaces are lined or made of aluminium. With the thermos flask the interior aluminium container keeps soup hot because while conduction is occurring on the inside aluminium surface and where there is zero reflected heat, the outer metallic aluminium surface is emitting or re-radiating only a tiny fraction of the heat of the liquid into a non-conductive adjoining cavity.

Further examples are when foil is wrapped around a cooked chicken or with an aluminium coffee pot and you press your hand onto the surface -100% heat transfer by conduction occurs, but once you draw your hand away, virtually no heat is felt. Why? Because the properties of aluminium foil are such that only 3% of the internal heat will be emitted from the opposite surface, but there must be airspace.

Foil insulation is commonly manufactured in roll form and is used in houses mainly to be fitted under roofs and on external walls for waterproofing and thermal insulation. It can be single or double-sided aluminium and is coloured on one side to indicate that this is the side which faces the sun for safety “anti-glare” reasons. In both walls and roofs, the dominant insulating surface of roll foil is the visible aluminium side which always faces into the building and, in conjunction with an efficient airspace, has two functions:

i) 3% low emitting surface - summer heat flow in

ii) 97% high reflecting surface - winter heat flow out

Aluminium foil airspaces produce maximum (or optimum) thermal resistance with:

i) Vertical airspaces - walls: minimum 20mm to 40mm wide

ii) Horizontal airspaces - ceilings and under floors: minimum 50mm to100mm deep,

ie less than 50mm or more than 100mm - the resistance decreases.

In walls, vertical foil airspaces have basically the same Rvalue heat flow sideways, in or out,

ie summer and winter are the same. In ceilings, horizontal foil airspaces have about 2-3 times greater Rvalue heat flow down than up, ie the summer value is much greater than for winter.

For winter heat flow out of buildings, the highest Rvalue for foil is achieved with the existence of still airspaces, ie no air movement. However, with summer radiant heat flow in, moving air against the surface of foil actually increases thermal resistance, ie foil airspaces in roofs, ceilings and walls gain a benefit in summer with high ventilation rates.

Concertina FOIL BATTS are segmented pieces of double-sided aluminium foil laminate which are innovative and unique in walls and floors because they are recessed and stapled between timbers to form uniformly deep foil airspaces producing constant, optimum and uniform thermal resistance. Roll foil, on the other hand, dished behind weatherboard walls or draped over floor joists has varying airspace depth and consequently changing or inconsistent thermal resistance.

WALLS

A timber frame house wrapped with aluminium foil insulation plus a Concertina FOIL BATT in the stud cavities will provide high summer and winter thermal performance.

FOIL BATTS in walls totally take the place of fibre batts, are self-supporting, rigid, cannot slump and split the one stud airspace cavity into two uniformly deep thermally efficient foil airspaces producing consistent unchanging Rvalue over the entire wall surface area – unlike dished roll foil if fitted behind plasterboard. Still airspaces on either side of the FOIL BATTS provide greater thermal resistance in winter than ventilated airspaces. In brick veneer walls, external house wrap foil makes a valuable contribution – three multiple foil airspaces are created, two are still and the cavity space is ventilated. Trapped still air is a good insulator, just like wearing multiple layers of clothing will keep you warmer than wearing one sweater. And every aluminium foil airspace has the capacity to be a low emitter or high reflector of radiant heat.

R1.5-2.0 fibre batts in walls must remain dry and need to be restrained from touching outer brick or clad walls because they can absorb moisture (increasing the risk of slumping) and transfer this moisture onto internal walls causing damage and loss of thermal performance. Outer foil wraps are commonly used as a waterproof and restraint device but the fibre batts are pushed into stud cavities making direct contact to the inner aluminium foil surface, which then transmits conducted summer heat directly into the fibre batts, which is stored and then transferred onto internal walls. In other words, the thermal contribution of the foil insulation (summer 3% emissivity, winter 97% reflectivity) is practically the same as brown building paper.

Western and eastern walls in southern latitudes such as Melbourne experience long periods of daily solar radiation in summer, as the sun sets very slowly compared to more northerly States. With cooler evening time temperatures, fibre batts in the walls continue to radiate heat into the house. Replacing the fibre batts with FOIL BATTS will create the vital non-conduction airspace to the foil wrap and it will now be impossible for any daytime summer radiation to penetrate inwards through the wall structure, achieving a Total R2.4 resistance compared to Total R1.7-1.8 for foil wrap plus R1.5 fibre batts.

Clad walls – fibre cement, blue board or timber such as unpainted weatherboard or western red cedar – must also be permitted to “breathe” by allowing the free movement of moisture vapour through walls, inwards or outwards. Tyvek breather paper or pin-pricked “breather” external foil wraps, dished slightly inwards between studs, assists the passage of moisture vapour to pass through into the stud cavity and dissipate or vapourise. Fibre batts pressed up against breather foil push the foil hard up against the cladding which restricts the free movement of air and it is more likely for a moisture buildup to occur between the foil and the cladding as well as the ever present possibility of moisture forming in the matrix of the batt fibres increasing the slumping risk.

However, with Concertina FOIL BATTS any moisture-laden air from the cladding is much more likely to freely escape into the two adjoining foil airspaces. An example of a total vapour seal behind cladding would be the use of foil styrene wall boards, which is a plastic barrier that cannot breathe unless punched holes are made. The FOIL BATT system does not vapour-seal walls and this is one important reason why the Timber Advisory Centre (Victoria) give their support to Concertina FOIL BATTS – refer to TAC letter attached here or on www.concertinafoilbatts.com - see testimonials.

FOIL BATTS are cut to fit individual cavities and are stapled to meet the top timber - nogging or top plate. It is not necessary for a tight fit top and bottom in the stud cavities. In winter, after radiation occurs from internal walls, convected heat starts to form in the vertical airspaces and, with a sizable gap at both top and bottom of the FOIL BATT, a rotational airloop could occur between the two foil airspaces. As stated earlier, moving air is detrimental to foil airspaces but only for winter heat flow out.

FOIL BATTS meeting the top (or bottom) timber will break the airloop possibility and thereby maximise winter Rvalue of these foil cavities. In summer, the walls of houses are best insulated with FOIL BATTS and foil house wraps forming up to three multiple airspaces operating which will never transmit high temperature radiant heat inwards, while also successfully stopping winter heat escape.

The Rvalue performance of aluminium foil insulations in walls is the same in both winter and summer.

FOIL BATTS in walls form approximately parallel and uniformly deep airspaces and have calculated Total Rvalues in brick veneer walls:

· Uninsulated brick veneer wall = Total R0.5

· FOIL BATT + Foil house wrap = Total R2.4 *R2.2 clad walls

· FOIL BATT alone = Total R1.7 *R1.8 clad walls

· Two FOIL BATTS = Total R2.5

· FOIL BATT + Tyvek breather = Total R2.1 *R1.8 clad walls

· R1.5 fibrous batt + Foil house wrap = Total R1.8-1.9 approx. *R1.7 clad wall=zero foil value

· Hebel Power Panel + FOIL BATT = Total R2.0

· Braceboard + Foil house wrap = Total R0.5

· Braceboard + FOIL BATTS = Total R2.0 approx

Foil wraps fixed directly onto braceboard have a zero foil airspace, contribute zero thermal performance and serve only one purpose - waterproofing the framed walls during construction. FOIL BATTS are a much better insulator with two fully functioning foil airspaces created in the stud frame cavity.

CEILINGS

As much as 87% of the heat passed down from the roof of a building may be transferred by radiation.

Foil insulations in horizontal or sloping positions have different thermal resistance in summer and winter – approximately twice the R-value heat flow down compared to heat flow up. This is why in both hot and cold climates, Concertina FOIL BATTS are recommended to sit over the top of bulk insulation in standard pitched roofs - they form unique triangular air pockets with low emitting downward foil

surfaces in summer which then switch and become high reflective surfaces in winter. FOIL BATTS provide maximum summer and winter benefits at ceiling level because this is the point of final summer heat gain and immediate winter heat loss, ie winter heat must be stopped at ceiling level and not be allowed to escape into the roof cavity. Concertina FOIL BATTS are more effective than a single layer of foil rolled out and laid flat on top of bulk insulation or the ceiling itself because the bottom triangular foil surface functions continuously with a series of airspaces and only a small % surface area of contact.

Bulk insulation works better in winter than summer because winter “convected” heat is gentle at around 24-27degC at ceiling level, whereas summer heat flow into buildings is very different, with roofs typically radiating downwards at 80-100degC. Bulk insulation is officially tested at a fixed 33deg maximum temperature and does not have guaranteed Summer R-values but rather guaranteed summer performance at only 33deg. This fact ought to be printed on the labeling of all bulk insulations.

See also Wren website – Thermal Performance & Truth about Rvalues.

The R-value performance of Concertina FOIL BATTS:

· LAID on top of any existing fibrous insulation, with triangular profile airspaces

* Summer Heat Flow Down = additional R1.0 approx (NB: triangular - difficult to calculate)

* Winter Heat Flow Up = additional R0.5 approx

· STAPLED between timber ceiling joists or roofing rafters

* Summer Heat Flow Down = Total R2.0 approx

* Winter Heat Flow Up = Total R1.0 approx

This illustrates that in dual HOT-COLD climates, a simple and effective insulation combination

in ceilings is continuous bulk insulation (no gaps) with a FOIL BATT, either on top or beneath. At least one foil radiant heat barrier is needed in Australian pitched roof spaces and two foils are recommended for sloping or cathedral roofs due to the close proximity of the ceiling to the high intensity radiation

– eg foil sarking plus FOIL BATT or two FOIL BATTS. In climates where heat entry dominates over heat loss, then there is a clear case that foil insulations be used alone, and bulk insulation totally avoided. Bulk insulations are not radiant heat barriers but rather radiant heat absorbers.

FLOORS

Insulating ground level timber floors against winter heat loss has historically been very difficult, impractical or too expensive. Dished foil over joists makes gluing or cramping of floorboards impossible. Expanding and stapling Concertina FOIL BATTS between timber floor joists is the answer and widely recognised as the best technique for insulating timber floors. FOIL BATTS are endorsed for use by the Timber Advisory Centre (Vic) as providing beneficial thermal performance against winter radiant heat loss as well as having 50-100mm deep breathing airspaces - refer to TAC letter on web. Strip flooring is a living organic material and breathes by contracting and expanding when absorbing and releasing moisture vapour. It is commonly sealed on top with polyurethane and therefore can only breathe downwards – FOIL BATTS do not reduce or impede the breathing ability of the timber flooring and are perforated for drainage of possible moisture passing through particleboard exposed to rain.

Sheet polystyrene insulating boards should not be used under timber floors unless there are defined breathing openings. Fibreglass batts need to be supported by chicken wire, mesh or strapping. Concertina FOIL BATTS are self-supporting and require no additional support devices.

FOIL BATTS have high thermal performance of Total R2.2 as downward radiating heat in winter is reflected back to the underside of the floor raising its temperature by several degrees - there is no convected heat loss from floors, only radiant. Commonly, heating thermostats can be reduced from 21 to 18degC causing heating costs to be substantially reduced. As in walls, because the foil airspace depth is constant and unchanging, FOIL BATTS produce a consistent Rvalue over the entire floor area whereas dished or draped foil has a varying Rvalue. This consistent Rvalue produces greater temperature stability of the entire timber floor. Also, the larger the house the larger the floor to wall surface-area ratio is, and greater is the need to insulate the floor. Note that gaps in floor insulation has little effect on total floor heat loss – while the reverse is true when insulating ceilings.

Lastly, to achieve maximum winter thermal performance, the sub-floor space needs to have still air. With clad walls, black close weave shade cloth fitted behind perimeter base boards will act as a wind barrier and deflect air movement from entering and exiting the sub-floor area. Alternatively, for elevated houses on sloping ground with open perimeters, the underside of floor joists can be lined (eg with roll foil with breathing holes) to create immediate stillness of the joist cavity and with Concertina FOIL BATTS stapled halfway down joist sides forming two 50mm foil airspaces within a 100mm joist cavity.

CONCLUSION

Concertina FOIL BATTS conform to:

Australian Standard AS/NZS 4859.1(2002) “Materials for the thermal insulation of buildings”

Further information can be viewed on www.concertinafoilbatts.com

Wren Industries is also a founding member of:

AFIA – the Aluminium Foil Insulation Association Inc. (Vic 1998)

www.afia.com.au

AFIA is a participating organisation on:

i) Industry Technical Advisory Committee of the Australian Building Codes Board (ABCB) in the creation of building energy efficiency measures, introduced into the Building Code of Australia being made effective State by State from 1 Jan. 2003.