Knauf Cavity Wall Insulation

Posted on October 27, 2016 by CCF

Full-Fill Cavity Walls

Full-fill cavity walls are the most popular method of insulation. Roughly 55% of all new build cavity walls are fully-filled. If you include refurbishments, it takes the total to 85% of all residential cavity walls.

The reason is simple: filling a cavity with mineral wool offers substantial savings compared to partial-fill solutions – sometimes as much 50%. You’ll be able to achieve the thermal performance required by the Building Regulations while saving anything up to £535 a plot*. There is also less chance that performance will be impaired by air flows within the cavity.



Earthwool Dritherm Cavity Slab 32 Ultimate

Knauf’s Earthwool DriTherm Cavity Slab 32 Ultimate is a high density mineral wool slab offering very high levels of thermal resistance for the thermal insulation in residential and non-residential masonry cavity external walls.

Thermal performance

Earthwool DriTherm Cavity Slab 32 Ultimate has a thermal conductivity of 0.032 W/mK.

Fire performance

Earthwool DriTherm Cavity Slabs are classified as Euroclass A1 to BS EN 13501-1.

Moisture resistance

Earthwool DriTherm Cavity Slabs contain a water-repellent silicone additive to ensure that no liquid water is able to pass through the slabs and reach the inner leaf of masonry. Tests by the British Board of Agrément (BBA) confirm that Earthwool DriTherm Cavity Slabs will not transmit water to the inner leaf. Nor will they transmit moisture by capillary action across the cavity or from below DPC level.

Meeting U-Values

* The stated U-value can be achieved with this thickness in a smaller cavity than necessary for the PIR Solution. Either reduce the cavity width to the Earthwool DriTherm 32 thickness or use 100mm DriTherm 32.

** 85mm+75mm required to achieve thickness

GREY: Thickness required is greater than the required cavity for PIR (0.022 W/mK) in this case either consider widening the cavity or call Knauf Insulation Technical Support Team for Advice on 01744 766666 or email

Technical advice

For further information contact your local CCF branch

Please note: The above u-value calculations are guidance notes only, provided by Knauf Insulation, for further information please contact Knauf’s Technical Support Team on 01744 766666 now or email