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Floor insulation
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Anne Thomas
Posted 2012-09-24 11:22 (#1130)
Subject: Floor insulation


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We are trying to decide what to do about a floor covering for our hall. I've so far crawled under the back (north facing) third of the house and installed 100mm sheep's wool and that has generally made quite a difference but the remaining area has a sub-floor space that is too narrow to get under even for me and I've managed some pretty narrow spaces! (With swimming goggles and face mask, I look an interesting sight when I emerge!)
Estimates for ripping up the chip-board flooring and sticking insulation underneath seem very expensive. We are now looking at thick carpet plus thick underlay.
Something like http://www.carpet-underlay-shop.co.uk/envirolay-54oz-felt-underlay-...
has a 3.42 tog rating and is made from a recycled wool mixture.
Whereas http://www.carpet-underlay-shop.co.uk/cloud-9-contract-carpet-under...
is recycled PU foam. and has a tog rating of 2.1
You can get a carpet which is over 2 togs.
What I'm not clear about is how to calculate how much thermal efficiency we should be aiming for, how to calculate R values from togs and whether it is a good idea to have a product that can 'breath' and therefore allows moisture to escape or one that is likely to be more waterproof and not have air moving though it. My feeling is that there is less of a need to worry about damp from below, as the sub floor space is quite dry, and a greater need to allow moisture to escape from the house to reduce condensation. We have heat recovery fans at each end of the house but the one room that has kingspan foam under it does get a lot of condensation but then it is probably the coldest room.
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Martin
Posted 2012-10-12 17:14 (#1136 - in reply to #1130)
Subject: Re: Floor insulation


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I hadn't looked into this before, but it's an interesting issue, lots of people have a similar problem. The tog rating is the temperature difference in deg C across the carpet when it's losing 10 watts/ sq metre, so a 2 tog carpet loses 10 watts/sq metre with a temperature difference of 2 deg C (weird unit!). So that means the tog rating is 10 times the R value - or the R value of a 2 tog carpet is 0.2 m2K/W. For comparison, the 100mm of sheepswool has an R value of 2.6, i.e. the sheepswool is about 13 times better than the carpet, not surprising because it's also much thicker. The combination of carpet and thick underlay might get you up to 0.5 or 0.6, so maybe a fifth as good as the sheepswool. If you're happy to have the hall colder than the living rooms, and disciplined enough to keep the doors closed, you could reduce the heat loss a bit more, but the answer is that you won't be able to get anything like as good a result with carpet and underlay as you will with insulation. Others in a similar situation, but with draughty floorboards rather than chip-board, may find a greater benefit because the underlay and carpet will reduce their draughts.

I think you're right that the issue to worry about with moisture is warm, moist air from the house hitting a cold surface in the floor and condensing - even if it was damp in the void, the cold air there will hold less moisture than the warm air in the house, so that is unlikely to be such a problem. So, the question is, will adding the carpet and underlay cool the flooring sufficiently to cause condensation? My instinct is that it won't, at least not unless the hall is incredibly humid!
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Anne Thomas
Posted 2012-10-30 18:37 (#1143 - in reply to #1130)
Subject: Re: Floor insulation


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Carpet now installed! One consideration is that whereas the original carpet had joins consisting of 2 carpets joined underneath going into the rooms and these seemed to have lasted 20 years or so the installers now don't seem prepared to do this and put metal bars over the joins. Because the carpet was so thick it ended up looking like somebody with a beer belly trying to hold up his trousers with a belt and there was a big gap under the doors and only carpet thickness with a metal heat conductor just where there might be some draughts at the door frame. I managed to persuade them to put insulation under the metal bars and it does look better and mainly nearly meets the doors and it should be 2.6 togs better at these places. Carpet installers seem only to think of the look rather than the function of carpets. They are now more used to being asked for a thin carpet for under floor heating than a thick one to keep the heat in.
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Anne Thomas
Posted 2012-11-12 08:54 (#1151 - in reply to #1130)
Subject: Re: Floor insulation


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The hall is much warmer and so far we haven't needed the heating on at all. It seems to have stabilised at about 13-15 degrees which is fine for a quick dash between rooms!
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