25 The membrane method
Adam Ford and John Mellor of Protect Membranes discuss how to achieve low U-values using membrane technology with low emissivity
Government’s target of 300,000 homes has recently been increased to 340,000 properties to be built in England alone, annually until 2031, to keep on track with demand, according to a 2018 report commissioned by The National Housing Federation. With greater emphasis on meeting this shortfall using alternative construction methods, offsite timber frame manufacture is increasingly seen as a proven method to reduce build programmes and improve cost efficiencies, and, with a precision in design that can be controlled within factory conditions, is currently the fastest paced sector within UK housebuilding. Construction of timber buildings is set to top 60,000 units in 2018, up from around 52,000 in 2016.
T What is the challenge?
Set against the backdrop of high demand, the need for efficient manufacture and maximisation of build space to maintain affordability, today’s specifier has to ensure that materials for timber frame construction can meet fabric energy efficiency requirements by delivering low overall U-values for the structure. Current Building Regulations Part L1A set upper limit U-values for each key construction element (roofs, walls and floors) as well as airtightness requirements within a structure. As the drive for energy efficiency continues, the Regulations also detail a Notional Dwelling specification, which is more onerous and demanding in terms of U-values. In the case of a wall, at least a 40 per cent improvement against the upper limit value is required. With the need to minimise energy loss from a property to lower the environmental impact, the architect needs to consider innovative ways to design a dwelling to ensure the notional specification is met yet is affordable to the end client.
Using low emissivity, reflective membrane technology with insulating properties within the wall structure is ideally suited to
he use of timber in construction is now seen as a key route to address the UK’s housing shortage. The
timber frame panel construction and is a good way to achieve these objectives.
How can the challenge be overcome with product specification?
The thermal efficiency of the structure must be optimised so that low U-values can be achieved for each construction element to meet the low Notional Dwelling specification requirements. Taking the wall construction as an example, the use of internal breather membranes within the timber frame panel facing two still airspace cavities either side of the insulation, can deliver added thermal benefits when used with a reflective, vapour permeable breather membrane fitted on the outer face of the sheathing board on the cold side of the construction and a reflective air and vapour control layer (AVCL) on the warm side.
This combination of products ensures thermal efficiency if installed with the reflective surfaces facing into the cavities, reducing the insulation needed within a timber frame panel while still achieving low U-values. This could mean a reduction in the thickness of rigid, high density PIR insulation boards or a move to fibrous or EPS insulation without impacting on the wall’s footprint, thereby maximising land space and affordability, yet delivering strong thermal performance. Designing air spaces within a timber frame wall panel
ABOVE
Protect TF InterFoil used in a timber frame wall construction with cavity trays, mineral wool insulation, and internal/external reflective membranes
BELOW
Protect TF InterFoil insulating breather membrane with reflective technology
ADF AUGUST 2018
WWW.ARCHITECTSDATAFILE.CO.UK
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