Loft Insulation

27 Sep 2018
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United Kingdom
Hi, I am hoping for some advice.

My builder has completed a loft and the building inspector has said the insulation is not sufficient as it has a u value of 0.22 and not 0.18. I have spoken to my builder and he says we could argue on the basis of height that additional insulation would not be good. Does anyone have any ideas of what might be an argument to be had here? Any particular height we have to hit?

The alternative is to add insulation on top of the existing plasterboard. Any idea of what would be enough to use? Can I put this on top and skim and paint? How do I know if this will be enough?

Many thanks for your help.
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Did the builder not follow the building regs drawings spec?

Have you made any other improvements in energy efficiency? new windows, or a new boiler etc?
in which case you could get a SAPS test done and prove it that way. (although it costs about £250-£300). Or it might pass anyway, especially as you changed your light bulbs from incandescent to low energy LEDS, just this week :sneaky:
Thanks for the reply. Unfortunately not as the Builder put in 100mm if insulation and not 120mm.

We have new boiler and windows and lights etc. All LED.

I thought the U value was for heat loss? Is it actually energy efficiency testing?
Was the builder supplied with correct drawings and descriptions? If so, and they’ve done it wrong, then they need to put it right at no cost to you.
0.18 vs 0.22 sounds like the difference between Kooltherm and regular PIR board to me, i.e. you could re-do without any increase in thickness using the better insulation.
If you don’t want to do that and want to put a layer over the top, I think it needs to be about 25mm of PIR to get it down from 0.22 to 0.18. But check that!
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Thanks, Builder was supplied but unfortunately did not stick to it.

I think I will investigate the Sap test option and if not work will go through the additional insulation.

Many thanks for the help.
As an FYI- I showed the calculation to the building inspector with the plasterboard etc, provided details of my new boiler, windows and lighting.

The inspector had accepted the shortfall on the basis of the other changes and granted the certificate.

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