Low Energy House - Breather Membranes
Warm air leaking out through gaps and cracks in the building envelope is a major cause of heat loss and wasted energy in buildings
Breather Membranes in Timber Frame Construction
Timber frame construction usually incorporates high levels of insulation within the roof, walls and floor and can achieve thermal values significantly better than the minimum requirements of Building Regulations.
Breather Membranes and Air Infiltration
Air infiltration through gaps in the fabric of a timber framed building will accelerate the rate of heat loss by convection and consequently reduce thermal performance. To counteract the problem, in most types of timber frame construction, it is normal practice to cover the External Face of the wall panels with a breather membrane.
Breather Membranes and Wind Driven Rain
A breather membrane will also provide a second line of defence against any wind driven rain that may penetrate the cladding. The breather membrane may also contribute to air sealing the wall and reducing ventilation heat losses.
Fixing Breather Membranes
In timber frame construction, the breather membrane is usually fixed to the panels in the factory but, if preferred, it can be applied on site as soon as the shell of the building is erected. Fixing the breather membrane at an early stage will protect and weatherproof the building until the cladding is completed but, in the preferred option of factory fixing, it provides important protection to the panels during transport and erection.
Breather Membranes in Timber Frame Walls
High performance breather membranes are typically flexible, non-woven sheet materials made from high density polyethylene. They are spun bonded and carefully engineered to provide the minimum resistance to the passage of water vapour while at the same time providing an airtight barrier that is watertight to a hydrostatic head of 2.0 metres.
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 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 substantially reducing the thermal efficiency of the wall.
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 is usually achieved by fixing a vapour control layer, with 100 per cent water resistance, on the inside of the stud frame, behind the wall lining.
Breather membranes provide protection to the building envelope, restrict air infiltration and deflect water while allowing moisture to migrate freely and safely to the atmosphere