In 2024, 4.8 million renters were living in cold, damp or mouldy homes, while in England alone, the NHS spends an estimated £1.4bn every year treating illnesses associated with living in these conditions. Integrated weather resistant barriers can form the first line of defence in timber frame homes. Brian Adams, Senior Director of International Business at Arclin explains more.
Mould forms when water vapour condenses on a cold surface. It can be extremely harmful to one’s health. Breathing in mould spores can lead to or worsen respiratory illnesses, including asthma, wheezing and breathlessness. They can also trigger allergic reactions, such as a runny nose, sneezing, coughing, red eyes and skin rashes.
Causes of damp in homes
There are three main causes of moisture that contribute to damp and mould within homes – penetrating damp, rising damp and condensation. According to the 2023 English Housing Survey (EHS), 5% of all respondents experienced damp, of which 3% was due to condensation with rising damp and penetrating damp both contributing 2%. If we assume a similar picture across the rest of the UK, this would equate to nearly 1.5 million households living with condensation or penetrating damp in 2023. The survey also showed the problem is increasing.
Penetrating damp can be an issue due to failures in construction or due to poor maintenance; damaged or degraded mortar is one of the main pathways for moisture into the building fabric in traditional brick and block homes. Condensation is more complex, though it can occur due to lack of ventilation, insulation or both.
Various building regulations relate to the control of moisture that can lead to mould. In England, these include Approved Document A ‘Structure’, Approved Document C ‘Site preparation and resistance to contaminants and moisture’, Approved Document L ‘Conservation of Fuel and power’ and Approved Document F ‘Ventilation’.
Together, these documents lead to the conclusion that homes must include a breathable membrane to prevent moisture penetrating timber panels, while allowing humidity to escape the building envelope to avoid interstitial condensation.
Protecting timber frame homes from damp that can cause mould, therefore starts with design, specification and construction.
Prevention is better than cure
As wood can be vulnerable to water ingress during the construction phase, timber-based panels must be protected from moisture. Any barrier must also act as a vapour control layer, allowing incidental water vapour to escape, preventing interstitial condensation.
Traditionally, this is delivered by housewrap, a loose product that’s secured against the timber frame to create a weatherproof barrier. There are, however, some limitations with this type of solution. If the housewrap is installed on site, timber is unprotected during transportation and when it arrives onsite, can get wet before the building is fully wrapped.
It also requires experienced installers because failure to undertake, sometimes complicated, detailing correctly can lead to weak points where moisture can penetrate. The nature of housewrap means that it can be prone to puncture and tears that can expose the panel to moisture and contamination, so even if it is installed in the factory, it would need to be carefully checked and repaired once installed. Failure to repair minor damage can become a major issue over time.
There is an alternative. New technology means integrated weather resistant barrier overlays, such as Arclin’s Arctek® Dryshell™, can be fused to OSB sheathing boards in the factory. These highly durable overlays act as a weather resistant layer that provides instant physical protection to the wooden structure.
Timber frame walls, SIP systems and cassettes arrive on site with the overlays in place, providing protection during transportation and installation. They also help speed up construction, because all installers need to do is tape the joints to achieve air tightness.
Integrated weather resistant barrier overlays help reduce the risk of moisture and dirt penetrating the timber panels during construction. While their vapour permeability allows incidental vapour that has entered, via internal leakage for example, to escape the building envelope to avoid interstitial condensation.
Given that mould in homes is on the rise and is putting lives at risk, prevention must start with good design and specification. Switching from housewrap to integrated weather resistant barrier overlays ensures that timber frame homes are protected from day one. They shield timber from damp during construction while allowing vapour to escape once the home is occupied, so housebuilders can deliver healthier homes that stand the test of time.