A lot of homeowners contact us to ask about the correct thickness of insulation that should be used on the assumption there is an optimum depth they should aim for. The truth of the matter is that many factors play a part in what depth to use and amongst the most common are:

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1. Budget – phenolic boards are the best insulant but are also the most expensive and sometimes an EPS board is a financial compromise

2. Structural constraints - the depth of cills and soffits and the closeness of cast iron soil stacks to the wall can also restrict the depth available

3. Green conscience – for those wanting a recycled wood fibre board the minimum depth is 60mm compared to 20mm EPS

4. Type of finish required – natural lime or a brick slip finish will both add around 15mm extra to a thin render finish

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These are by no means the only issues but should give an idea as to why there is no perfect depth. Whilst the Building Regs Part L1B state as 0.35 u value is desirable for retro fits it also recognises the restrictions present and allows for any depth as long as that depth is the best available for the property given technical and financial restraints.

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As a general guide on a 9 inch solid brick wall a 40mm phenolic will hit 0.44 the same as a 6omm mineral wool or EPS board and a 60mm phenolic will hit 0.29 U value ie a new build standard with a 50mm phenolic hitting 0.35 ie Building Regs gold standard for existing houses.

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For more information or to speak to one of our advisors please call now on 08456 345866

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