One of the most significant alternatives to housewrap that addresses weaknesses is integrated vapour-permeable overlays for OSB sheathing boards, such as Arctek® Dryshell™. The proprietary layer is bonded to OSB, creating a product that is moisture resistant and vapour permeable.
Timber frame construction is considerably more common in the USA and Canada, where there are more alternatives to housewrap are available. When looking at options that perform the same function as housewrap, it’s important to be aware in which market a product is available.
What function do housewraps perform?
Housewraps are installed to the outside face of timber framed structures to act as a vapour-permeable ‘breather’ membrane behind the chosen external finish, such as a brick outer leaf. They help to resist the ingress of rain while allowing moisture vapour within the structure to escape to the external air.
Housewrap products are also commonly marketed on the basis of their ability to improve airtightness, thereby helping to retain warm air within dwellings.
‘Breathable’ membranes for roofs – whether vapour permeable only, or air and vapour permeable – are designed to perform a virtually identical function. The principal difference is that a housewrap can be left exposed for a period of time whereas roofing products should generally be covered up as soon as possible.
Also, a roofing membrane is unlikely to carry third-party certification for use on walls.
What issues are there with housewraps?
Traditional wraps are nailed and stapled to the timber frame to secure them in place, which introduces the risk of them being ripped or torn. Experienced installers may be able to wrap a property quickly, but there remains a risk of damage occurring during installation, especially in windy conditions. On-site manual processes may also need to be assessed from a health and safety perspective.
The correct lapping details must be observed for the wrap being used, including the right overlap measurements, ensuring that laps go in the right direction (upper pieces lapping over the sections below), and staggering sections of wrap to prevent joints coinciding.
Site installation of a housewrap means the installer must deal with tricky details, especially at window openings. Particular care is required to cover the lowest timber with the wrap. Any failure in detailing during installation risks moisture being able to penetrate behind the wrap and into the frame structure.
What can be used as alternatives to housewrap in the UK?
For timber frame specifiers or installers looking to move away from housewraps, what can they select instead? Modern housewrap membranes have replaced older solutions like asphalt paper.
Thermal insulation products – either in the form of insulation boards acting as sheathing, or flexible foil products (including bubble foils) – might be considered. Few will provide both moisture resistance and vapour permeability. In the case of rigid insulation boards, a membrane product is likely to still be required.
One of the alternatives to housewrap that can be adopted by OSB and timber product manufacturers is Arctek® Dryshell™. The factory-applied overlay fuses to OSB boards used in timber frame cassettes or SIP panels, offering moisture-resistance and vapour-permeability with improved airtightness.
Timber framed housebuilding solutions using Arctek® Dryshell™ arrive on site with the layer already in place, removing an installation step to save time and reduce labour costs. There are no tricky installation details, there is no risk of rips or tears, and no moisture can get into the construction once all joints have been taped.
By choosing Arctek® Dryshell™, timber framed housing manufacturers and suppliers can make improvements to their processes and take greater advantage of the growing timber frame market in the UK. To find out more about how Arctek® Dryshell™ can benefit your timber framed housebuilding projects, request a sample or contact us with an enquiry.
