January 29, 20251 yr Hi all, I have just had a shell extension completed. I have a suspended timber floor with a large void underneath. The new part of the extension also has suspended timber floors but the void is no as big however there are lots of telescopic vents around and the sleeper walls are honeycomb constructions so plenty of air floor. I wan't to insulate the ground floor to keep heat in and would like to insulate with PIR Insulation to get the required u value. I have read conflicting information online about insulating suspended timber floors and the effect it can have on the joists. Whats your thoughts and has anyone here done it?
January 29, 20251 yr PIR is a mixed blessing as many will tell you. V hard to get a perfect fit and as humidity changes a 'perfect fit' may not be one any more. I like flexible wood-fibre, but it is not cheap and will need just short of twice as much as PIR for the same U value. The main thing with UFI is that as you warm up the room you cool down the floor structure, increasing the risk of condensation. Excellent cross-ventilation (no 'blind' areas) can help a lot. Beware that UFI does not always appear to obey the laws of Building Physics! Edited January 29, 20251 yr by Redbeard
January 30, 20251 yr yeah ive done it and added UFH and as far as i can tell its fine. Significantly warmer than without it but it was backbreaking/soul destroying work, even putting the tape on took days and days. Thankfully once in a lifetime. Insulation saw in the jigsaw, PIR, Illbruck FM330 foam, aluminuim tape, plenty of painkillers.
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