Skipweasel (none@127.1.1.1) wibbled on Sunday 09 January 2011 19:01:
He'll have to watch the elecrics - proably OK on most circuits with 100mm insulation covering, but if heating pipes are being buried near the cables in fibre it is quite likely to put the cable out of spec.
Gotcha.
I've seen slings used to support insulation a couple of times and it's not looked particularly good, compressed near the edges and sagging in the middle. Tricky to fit too unless all the floor is up.
It was that reason that made me support my stuff with hardboard (see other post). With the developments in materials I'd probably do it differently now but with the mylar covered fibreglass stuff virtually being given away these days it might make sense still to use that.
I'm thinking of putting tile laths on top of the sleeper walls between the joists (with intermediate support if necessary) to support a pull through of spaceblanket (the mylar covered fibreglass stuff), Anyone see any gotchas?
el
I think you might be OK if you used oversized space blanket, which would squash up aainst the joists.. Mr Thumbs's plan is what I was originally going to do. For 400 joist centres you could use 600mm space blanket. Though I couldn't find the 600 anywhere. B&Q are doing king size (1140mm wide) space blanket at 6 quid a 4 metre roll, though'll you probably have to quote the web price and get them to order it in, as it goes out of the shop as fast as it comes in. I was going to use that, cut in half lengthways - space blanket is a mineral wool made from recycled plastic, and from looking at some damaged rolIs I think it holds together quite well - alternatively you could cut it and gaffer tape the open edge before use.
Sounds like a plan if you want to take up a minimum of floorboards. I decided to bit the bullet on that.
Cheers Richard
I am about ready for a new carpet in lounge, how effective is a good thermal underlay and thick carpet in insulating the floor in comparison with thermal insulation under or in between joists?
Is there a rigid foam board that has good insulation properties that can be placed on the existing boards before laying thermal underlay?
It might take an inch or so off the height of room but is this a possible easier route to insulating a suspended floor?
Don
Pretty good, but seal the cracks first: over old boards, tack down hardboard and use foam or mastic at the skirtings.
Its possible. But really, ripping up a floor of boards is no big deal.
Having spent most of the weekend "ripping up a few floorboards", no, it's not a huge deal, but it's probably worth avoiding if you can. If you were going for fitted carpet you could, I suppose, add 25mm Celotex over the floorboards, and flooring chipboard over that. There are probably insulated boards that would do both jobs at once.
There will be hassles either way. It's harder to get floorboards up with the skirting in place. Fortunately I was ripping my skirtings off as well. Even then I had to hack off some of the plaster and render that came down over the ends of the boards - most of the boards went the full length of the room, though I've cut them for relaying, for manoeuvrability.
It's hard to get up all the boards in one room without doing some damage to some of them. I took out the first board by cutting out the tongue with a jig saw (stopping at the joists and using a hand floorboard saw for that bit, and being certain that there were no cables where I was cutting), then punching the brads through before prying up the board. Then I removed two sets of three boards together, cutting out the far tongue and using a trolley jack with a bit of wood to spread the force under three boards at a time (which has the disadvantage that it wants to lift the joist as well, until the brads pop out). This gave me enough room to use three foot of 4x2 as a lever to take up the rest of the floor, with another 4x2 across the joists as a fulcrum. I lost the undersides of a few grooves, which won't be visible when the floor is relayed. The biggest damage is some enlarged and splintered holes where I removed the brads after the boards were up. They won't look as bad when I've sanded and varnished them before relaying.
The advantage of taking the boards up and insulating underneath, to my mind, is that I will still have access to the void under the boards and above the insulation, for cabling and heating pipework. I also want vanrished floors with rugs, rather than a fitted carpet.
25mm Celotex on top of floorboards, with board over and carpet on that, would avoid all the above. However, in raising the floor by an inch you would still have issues with skirtings (though you could just go up to the existing an accept that they'd look shorter), door casings, and the doors themselves would need taking off and trimming. Either you' have to do every room on that floor, or you'd have a step. And you'd have no access to the underfloor. I think if you don't want to take the floor up, you'd be better off just with a thick underlay and carpet, or possibly one of the thin foil insulation rolls mentioned earlier in this thread. Something that's going to cut out draughts and make your floor somewhat warmer, without raising its level noticeably.Cheers Richard
In article , snipped-for-privacy@privacy.net writes
Don't underestimate the faff factor of fitting lots of battens and supports when you're working away down there. I also couldn't see the spaceblanket sliding over the supports that easily when getting it into place, hence the reason I boarded it with hardboard shiny side up so it could be slid in easily.
Also, make sure you compress the insulation just a little, you don't want any gaps between it and the floorboards where is slumps with age or droops between supports.
Why not, as long as there are no gaps between the insulation and the joists?
Cheers Richard
It's to avoid any risk of draughts passing over the top of the insulation, it doesn't take much air movement to negate the benefit of the insulation so I think it's safer not to leave a gap.
In a similar but different situation I have seen walls being insulated
80mm Celotex without thought for the howling gale that is free to circulate from the underfloor to the small space between the insulation and the plasterboard.
Thatswhy you tape over the whole shebang with foil tape.
Where are the draughts going to come from, if there are no gaps between the insulation and the joists?
The bottom of the plasterboard will be screwed either to the sole plate of the studwork that the Celotex is fixed in, or if the Celotex is screwed to battens, it will be screwed through the Celotex to the bottom batten. So, what small space?
Cheers Richard
The obvious place is at the ends of the joists, in my case, that is where my vents are located. Also, in my case, the joist are formed by 3 pieces of 6x3 lapped end to end and supported on 8x4 cross pieces. This means transitions in the side surfaces where the insulation is to seal. Placing the fibreglass in intimate contact with the floorboards meant that I didn't need to worry about little gaps here and there that might have turned a cavity above the insulation into wind tunnels on a windy day.
The way I have done it means that small faults at installation or developing later are less likely to negate the effectiveness of the insulation.
In the case I am thinking of there was no sole plate and not a continuous batten at the bottom so air was free to circulate ala conventional lath and plaster construction. It's not how I would have done it but the builder could not see anything wrong with it. It was a retrofit to a 1900 build tenement btw.
Obviously your vents or air bricks need to vent under the insulation, by means of a box or a duct if necessary. And if you haven't paid attention to eliminating gaps between the insulation and the joists, why wouldn't those gaps go right to the top and negate your efforts in squashing the insulation under the floorboards?
Much better to ensure that your insulation is wider than the gap between joists, and is both properly supported underneath and squashed in firmly between the joists, eliminating gaps. Any dead air between insulation and floorboards is then working to your advantage in helping to insulate the floor.
The plasterboard would still be screwed firmly over the Celotex, so it's difficult to see how a gap could exist. And you were talking about a supposed space between the plasterboard and the Celotex, so where does lath and plaster come into it?
Cheers Richard
You're clearly an expert at this, good luck with your implementation.
No I'm not, but I'm not as confused as you seem to be.
Cheers Richard
In article , geraldthehamster writes
No confusion here, I have working underfloor insulation using fibreglass that employs safeguards to avoid it being negated by air leaks that I view as inevitable or at least possible with the ravages of time.
The decision to do it that way was based on the practical experience of doing it myself and the suggestion to follow a similar design is the product of that experience.
You're free to take that on board or follow your own path.
Once again, good luck with your implementation.
I'm sure your insulation is fine, because it's not a precise art. Imaginary howling gales notwithstanding ;-)
Thank you for your good wishes.
Cheers Richard
Another question: it might turn out to be easier for me to fit the Celotex between, rather than under the joists (with the edges sealed with PU foam, to avoid howling gales, tsunamis, etc.). The disadvantage as I see it is that there is no insulation under the 4x2 joists. Does anyone think the cold bridging would be significant?
Cheers richard
geraldthehamster ( snipped-for-privacy@hotmail.co.uk) wibbled on Wednesday 12 January
2011 09:27:
No, not that you'd notice.
What might be the easiest way is to upscrew some 4" "legs" unde rthe joists,
1" poking out each side, 2" bits on the side adjacent to the bottom edge at intervals (every 2-3 foot should be enough) to suppoort the celotex at the correct height while foaming in.HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.