Thermal performance in masonry cavity walls using mineral wool solutions

13.10.2016
Blog Post
Knauf mineral wool

Even though building regulations relating to energy and thermal insulation in England, Wales or Scotland haven’t changed for some time, Knauf Insulation are aware of concern and perhaps misconceptions that mineral wool solutions might not deliver the u-values needed in masonry walls.

There are different u-value requirements for different types of work and these are also different in each country!

The table below shows the u-value and required thickness of Earthwool® DriTherm Cavity Slabs for masonry walls in extensions to existing buildings.

Table 1

Country Maximum U-value Thickness of Earthwool DriTherm Cavity Slabs
England -  AD L1B and AD L2B 0.28 W/m2K 100mm Earthwool DriTherm 32 
Wales – ADL1B and ADL2B 0.21 W/m2K 150mm Earthwool DriTherm 32
Scotland Tech Standard 6 (Domestic) 0.19 W/m2K or 0.22 W/m2K 150mm Earthwool  DriTherm 32
Scotland Tech Standard 6 (Non Domestic) 0.25 W/m2K 125mm Earthwool DriTherm 32

* ​You will also need to consider whether a full fill insulation solution is suitable for your locality.

The Approved Documents also set a ‘backstop’ maximum u-value for any part of individual construction elements, independent of the u-values. This allows greater flexibility in design but minimises the risk of surface condensation and mould growth occurring on or within any part of an element. However, for dwellings in England and Scotland, the building is unlikely to comply with a wall built to the backstop requirement, whereas in Wales it would.

Table 2

Country Backstop U-value KI Suggested U-value

Thickness of Earthwool DriTherm

England -  AD L1A  0.30 W/m2K 0.21 to 0.25 W/m2 100 to 150mm Earthwool DriTherm 32
Wales – AD L1A 0.21 W/m2K 0.21 W/m2K 125 to 150mm Earthwool DriTherm 32
Scotland Tech Standard 6 (Domestic) 0.25 W/m2K 0.19 W/m2K 150mm Earthwool DriTherm 32

* ​You will also need to consider whether a full fill insulation solution is suitable for your locality.

Knauf Technical Support Team can offer help to achieve overall compliance.

For further information, visit: http://www.knaufinsulation.co.uk/design/technical-support-team-tst 

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.

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