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Insulating suspended timber floors from below |
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| message from Stuart Roebuck on 13 May 2004 |
Has anyone got any advice / experience of insulating suspended timber
floors from below (e.g. without removing the floor boards)?
The http://www.est.org.uk/bestpractice/ site contains some useful
pointers indicating that this is something that can be done and is
sensible to do.
They suggest either a rigid insulation (e.g. extruded polystyrene)
supported by nails or battens in the joists, or 'loft insulation'
supported by netting stapled into the joists.
However, they caution letting the polystyrene come in contact with
electrical cables which can go brittle, so that restricts that
suggestion, and they say that any insulation needs to be kept in contact
with the floor above, so the idea of suspending loft insulation by
netting seems practically impossible.
Hence the question - has anyone actually done this? What are the
practical solutions?
Cheers,
Stuart.
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| John Bramley replied to Stuart Roebuck on 20 May 2004 |
I did this at the start of the year to stop some of the draughts through
the floor.
I didn't fancy using polystyrene because of the problems with electrical
cables you mentioned, and also I was slightly worried that moisture in
the air might condense on the top of it (don't know if that would really
have been a problem). I went for rolls of loft insulation instead
because I figured it would be able to 'breathe'.
I suppose that is to stop draughts getting around the sides/ends and
circulating above the insulation.
Well it was quite easy with rolls of loft insulation that were slightly
wider than the distance between joists. I just unrolled lengths of
insulation and pushed it between the joists (parallel to them) and it
mostly stayed in place by itself. It is quite thick and springy so
pushing it up into place meant that it was in contact with the
floorboards. I didn't use netting to hold it up, and instead used
string stapled to the sides of the joists under the insulation, in a
zigzag fashion.
All in all it was remarkably easy - the worst bit was looking up and
getting dust falling in my face, and lying on the rubble in the void.
The room seems a bit warmer now, although the vast expanse of glass in
the bay window is the biggest loss of heat, but that would cost a lot
more to do something about, for now thick curtains make it quite cosy at
night.
John.
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| Michael Mcneil replied to John Bramley on 20 May 2004 |
"John Bramley" <john@nospamplease.com> wrote in message
news:c8iti4$d1$1@pump1.york.ac.uk
I thought polystyrene was a fire hazard.
You can put the rockwool/fibreglass in a cover some manufacturers sell
it in plastic bags.
Wear old rags to do the job and sling them after. Then shower in cold
water to stop the glass getting into your skin as it will with an hot
shower. I hate that stuff too bits!
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| RichardS replied to Michael Mcneil on 21 May 2004 |
<snip>
I asked the manufacturers of Wickes' standard 50mm polystyrene sheet
insulation about this (Wickes couldnt' tell me whether or not it was fire
retardent). I think that they said that Jablite was another one of their
products, they're based near Hull, have lost their details.
For in-wall insulation, roof-space insulation and non-ground floor
insulation yes, it does need to be fire retardant.
For ground floor insulation it doesn't, even under timber suspended floors.
Their technical department said that they had been to fire investigations
where their products had been installed, and the insulation was found to be
intact and untouched by fire (though as someone pointed out when I posted
this before, no surprise there, as heat rises...).
I specifically asked them whether the product was suitable for installation
under a suspended wooden ground floor (no cellar) and their answer was a
definite "yes". If they'd just been trying to make sure I used their
products then they would have recommended that I search out one of their
fire retardant products, so I think it was sales-neutral advice.
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| Stuart Roebuck replied to John Bramley on 20 May 2004 |
John,
Thanks for that feedback - very helpful. I'll be trying it myself in a
month or two's time!
Stuart.
In article <c8iti4$d1$1@pump1.york.ac.uk>,
John Bramley <john@nospamplease.com> wrote:
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| G&M replied to Stuart Roebuck on 20 May 2004 |
As well as using Rockwool as insulator between the joists, rather than
netting we used Airtec from Screwfix pinned to the underside of the joists.
This forms a reasonably airtight seal to keep moisture out and adds some
insulation, though we also added a small fan to force air around the
underside and prevent any condensation forming on the underside of what is
now quite a lot of insulation.
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| Stuart Roebuck replied to G&M on 21 May 2004 |
It sounds like in your situation you were trying to protect against a
fairly damp cavity below.
Under normal circumstances, wouldn't sealing under the joists go against
the normal advice of maintaining ventilation to prevent rot? If I
understand you correctly the fan is only increasing the venting below
the seal and doing nothing to vent the joists and boards above.
On a different point - are there any advantages/disadvantages in using
Airtec instead of rockwool as the insulator, and is there any notable
heat insulation loss in pinning (stapling?) this on?
All thoughts and comments much appreciated,
Stuart.
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| G&M replied to Stuart Roebuck on 21 May 2004 |
Yes - damp earth. Water table is roughly level with the earth.
The Airtec has been sealed all round so no damp should rise from below, but
any damp within the joists can still rise through the Rockwool and up
through the natural holes between the floorboards. At least that's the
theory :-)
I used both - had already used normal plastic sheet to support Rockwool
under the conservatory but then Screwfix had Airtec on offer so thought I'd
give it a try with the Rockwool. Agree that the pinning will cause some
heat transfer but shouldn't be great. The Rockwool is the prime insulator
anyway.
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| David replied to Stuart Roebuck on 21 May 2004 |
Its treated now with a fire retardant or at least building grade
polystyrenes are.
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