Low Energy House - Reflective Membranes
Breather membranes are woven fabrics which are used to prevent water entry to the construction while allowing vapour to escape. The additional function of heat reflecting membranes is to block infrared energy radiating across an air space
Installing a reflective breather membrane in a timber frame system enhances the thermal characteristics of the wall and roof cavities, thus improving the insulation performance and reducing the U-value of the total building structure.
When installed facing into an unventilated airspace, reflective breather membranes effectively block infrared radiation, enhance the thermal performance of the airspace, and consequently increase the overall U-value of the construction.
Reflective Membranes - Keep the House Cool in Summer
In summer, infrared energy from the sun is easily absorbed by the roof and walls. Excessive heat can penetrate the building’s insulation layer through conduction and convection, eventually radiating to the interior, causing a rise in the internal temperature. If a heat reflective breather membrane is fixed to the External Face of the timber frame construction such a temperature rise can be avoided.
Reflective Membrane Construction
High performance reflective membranes are typically made from high density polyethylene, spun bonded and with an aluminium coating on one face. They are usually airtight, watertight (to 2 metres) and offer very low resistance to the passage of water vapour. Most importantly, they reflect 94 per cent of radiant heat.
Moisture Transfer Through Reflective Membranes
Reflective breather membranes effectively manage moisture transfer while shielding the building against heat transfer. They have a micro fibre structure combined with a very fine aluminium coating. The result is a ‘vapour open’ structure that allows the construction of an air tight envelope. Their aluminium coated surface has very low emissivity which can minimise heat losses in winter and reflect the heat in summer to achieve a comfortable energy efficient house.
Reflective Vapour Control Layer (Vapour Barrier)
Although a vapour control layer is not a breather membrane it is an essential element in the effective management of moisture transfer through a timber frame.
In a heated building, internal vapour from the kitchens and bathrooms will tend to drive moisture through the building envelope. If that water vapour meets a cold surface it will condense, causing damage to the timber frame, and will substantially reduce the thermal efficiency of the wall or roof.
In order to stop water vapour penetrating the timber frame construction, it is normal practice to ensure that the Internal Face of the wall has more resistance to water vapour than the external face of the frame. This can be achieved by fixing a reflective vapour control layer, which is water impermeable, on the inside of the stud frame, behind the wall lining.
Air Leakage Barriers
The installation of a reflective vapour control layer, as an air leakage barrier, will help reduce the rate of heat loss through the building fabric by conduction, convection and radiation.
Reflective membranes, as well as providing protection to the building envelope, restricting air infiltration and deflecting water, also reflect radiation