Warm, dry, full fill cavity insulation

Increasingly stringent energy efficiency standards in the building regulations are encouraging the adoption of new cavity wall insulation techniques and materials. However, it can often be tricky to make the right choice to meet the correct standards.

When partially filling cavity walls, a 50mm residual cavity must be maintained in external walls - particularly in areas of severe exposure to wind-driven rain where fair-faced masonry is the external finish. Where severe exposure is an issue, it is common to clad or render the outer face of cavity walls and so allow the cavity to be fully filled.

To meet current energy efficiency requirements, the cavity size now needs to be at least 100mm in new build homes. Fully filling the cavity with glass mineral wool is still a popular choice with many builders - not only is the installation easier, but it’s also still possible to meet very low U-values with either 100mm or 125mm cavities as detailed below:

Rain penetration confidence

In areas of extreme exposure, a cavity of 100mm with full fill insulation can be used in conjunction with render or an impervious cladding. The cavity width requirement decreases to 75mm and 50mm respectively in less exposed areas and can be used with fairfaced masonry without the cladding as accepted by LABC Warranty. See chapter 7.1 of the LABC Warranty Technical Manual for further guidance.

Solutions such as Knauf Insulation’s Earthwool DriTherm Cavity Wall products are ideal for such situations. The glass mineral wool insulation solutions have passed rigorous rain penetration tests set by the British Board of Agreement to show the wall does not permit water to track to the inner leaf.

Backed by a proven track record of more than 40 years, the cavity wall product range, which is in the process of obtaining LABC Registered Details certification*, comes with a 50-year moisture guarantee.

*Subject to final confirmation.

Please Note: Every care was taken to ensure the information was correct at the time of publication. Any written guidance provided does not replace the user’s professional judgement. It is the responsibility of the dutyholder or person carrying out the work to ensure compliance with relevant building regulations or applicable technical standards.