floor or roof insulation

Hello everyone,

My semi detached house loft has a loose fill material and has been floored with normal woodchip flooring. I was thinking of upgrading the insulation but rather than lift the flooring I thought I would put the insulation onto the inside of the roof. Is this a good idea and what type of insulation should I use? I envisaged using glass fibre rolls but how would I keep it in place? All suggestions welcome, Jackie

Reply to
Jackie
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sorry I meant chipboard

Reply to
Jackie

Whether it is a good idea or not will depend on a few things...

The roof timbers need ventilation to ensure they stay dry and free from rot. If you stick a layer of insulation under them you can potentially cut off the air flow to them, and in time cause more serious problems.

The way round this is usually by arranging for some air flow behind the insulation using either a breathable under tile felt, or soffit and ridge vents.

One way is with a rigid PIR foam insulation board. Well known trade names include Celotex and Kingspan, but there are plenty of other brands that make the same stuff - often cheaper. This can be wedged into place between rafters, and screwed to the underside of them.

There are some pictures here:

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Reply to
John Rumm

related to what John wrote above:

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as I mentioned in a reply to another post a few hours ago, the place to buy cheap insulation board from is:
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Reply to
Lobster

fibreglass insulation. I don't want to insulate the rafters as it will reduce the headroom, and will be difficult to ventilate. I could get 90mm kingspan (or equivalent) under the boarding (floor) between the (ceiling) joists, possibly supplemented with 50mm above the joists. Are there any pitfalls in this approach?

Reply to
<me9

It will work... Remember that the better insulated it is, the colder it will get. That means you will need to take more care preventing any tanks/pipes from freezing (that will apply pretty much to any insulation you fit).

The solid panels obviously need to be cut to fit (which is the advantage of the fibreglass stuff - you can stick that in quite quickly), the ones over the joists however can just be screwed down in a few places and then the boards laid directly on them (it is quite tough in compression)

Reply to
John Rumm

I only have one layer of (off the top of my head around 40-50mm) fibreglass loft insulation. I've boarded half the loft (screws, so can be moved), and I'm thinking about improving the insulation, both because the house gets bloody cold upstairs in winter and also because of fuel costs. Does anybody have any links that point to the relative efficiency of insulation methods. I will be going for the floor insulation as I also don't want to lose headroom, and would like to know how my rough and ready current fibreglass compares against the above boarding, and also how a floored loft (standard shed loft chipboard) compares against non-floored (hey even chipboard must insulate to some extent!). A quick google didn't find any straightforward links.

Reply to
mike. buckley

Good load of figures in this document:

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the fibreglass stuff:

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they are showing figures for two layers of (thicker) wool that you have)

Adding flooring to an uninsulated loft will help (more by virtue of ther trapped layer of air than the chipboard itself), however compared to a real insualting product the chipboard iteself is relatively insignificant.

Reply to
John Rumm

In message , John Rumm writes

That's interesting thanks.

I've had a look in my loft and I seem to have variable joist widths (3400->3700mm), but I reckon I'll be able to cram better insulation in than I currently have. The property (1938 semi) has been re-roofed at some point, and a lot of debri has been left over the plaster which the current fibreglass rolls are sitting on.

I had a look in one of the sheds at lunch and they had 150mm, 170mm and

200mm rolls, but when they are wrapped up they feel nothing like that size! I think I'll probably get a couple of rolls and see how it goes, the site above assumes double layer over the joists, but I want to put chipboard down, so that's not an option for me. Hopefully with the more modern foil backed fibreglass I'll get better insulation than the current fairly haphazard fibreglass.
Reply to
Mike Buckley

You could fill between the joists with the fibreglass, but then lay a ridgid panel right over the joists and put the chipboard down on that. (a bit like you make flat roofs these days).

Much of the stuff is not foil backed (unless you explicitly go looking fot it!). There not not much point compressing more into the joist space than fits normally, since it is the trapped air that does a fair amount of the insulating)

Reply to
John Rumm

Hmm, need some long screws to secure it all - but that sounds a good idea.

I just randomly looked at the first stuff I came to in the shed, it was foil backed and plastic wrapped, which you just lay down in the joist space and cut the ends as necessary. The rest of the stuff was about 3 miles up on the top shelf, so I could see neither price nor quality. Trip to a builders merchant methinks.

Thanks for the advice.

Reply to
Mike Buckley

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