UK construction is under pressure from regulation and taxation to build better and greener. With the government wanting to deliver more homes the Construction Industry needs new strategies to boost performance, quality and output. Weather resistant barriers will be one of the solutions that will support this.
Future Homes and Buildings Standard combats emissions and drives building fabric efficiency
New dwellings will need to meet the FHBS from December 2027. The expected requirement is that new-build homes produce 75-80% less carbon emissions.
The new standard will require better building fabric efficiency, with enhanced air tightness, thermal bridge reduction and higher R (heat resistance) values for walls, floors and roofs from improved insulation levels.
Timber frame can deliver superior air tightness
Timber is a natural insulant, helping to regulate indoor temperatures and reduce energy consumption for heating and cooling. Timber Frame’s precisely engineered components, combined with its capacity for accommodating high levels of insulation, minimise air leakage and delivers superior airtightness.
Pros and cons of weather resistant barrier types
Weather resistant barriers perform vital roles in timber buildings. They protect wood building products from the elements on-site and can enhance airtightness. Vapour permeable variants also allow internally generated moisture to escape the building envelope.
Plastic based house wrap type weather resistant barriers
The most commonly used products are polyethylene or polypropylene house wraps. These are applied to the exterior of the envelope in the factory or on-site using staples or nails. They are relatively cheap. However, they can snag and tear during application, especially in adverse weather. To achieve the right overlapping and joint sealing also requires site skills and experience which are increasingly in short supply. Moreover, they add a process to timber frame erection, offsetting its inherent quick build benefits. They also result in waste offcuts.
Building paper weather resistant barriers
A long-established weather resistant barrier is building paper, which comprises kraft paper impregnated with asphalt. This delivers water resistance, but its weight can make it cumbersome. It is also less flexible than the plastic alternatives and, perhaps even more so than the latter, requires skill to fit. It can crack and tear during installation and over time can dry out and become brittle. It also lacks vapour permeability.
Peel and stick weather resistant barriers
Manufacturers say peel and stick, also known as self-adhered weather resistant barriers, represent a technical advance on house wrap membranes and building paper. Generally, an adhesive primer is applied to the timber frame envelope, the backing of the weather resistant barrier is then peeled off and the product fixed in place. These tend to be more expensive, but producers maintain they still only represent a small fraction of overall build cost.
They do however also require experience to ensure there are no gaps where moisture could enter. This adds a process to the build and is best not applied in wet conditions. Moreover, they always require an adhesive primer used with OSB (Oriented Strand Board) because of its uneven surface.
Liquid-applied weather resistant barriers
Brush or spray applied liquid weather resistant barriers represent a further step up in technology and also price. They are claimed to give better water resistance and airtightness than plastic membranes and self-adhered products. But they too need skill to use effectively and achieve the right wet thickness, and they add to build time.
Thermally fused weather resistant barriers
Thermally fused weather resistant barriers do not add a further stage in timber frame construction. They are a proprietary resin formula overlay, that is an integrated solution, applied to wood-based panels in the panel producer’s factory. This ensures uniform all-round protection coverage and consistent quality, with the wood panels protected when they get to site. Thermally fused weather resistant barriers such as Arctek® Dryshell™ are vapour permeable, preventing build-up of interstitial condensation in the envelope.
Deskilling the weather resistant barrier process
Instead of adding to construction time, thermally fused weather resistant barriers enhance the inherent quick-build benefits of timber frame. They also deskill the weather resistant barrier process, being applied under heat and pressure on automated lines in factories. It is estimated that to satisfy housing demand in the UK, we need 250,000 construction workers by 2028. Labour-saving technologies, like thermally fused weather resistant barriers, are set to become ever more relevant.