Dormer bungalow - insulation under slope?

One question I forgot to raise - what kind of insulation should be put down here?

I guess ideally polyboard should have been put down and screed poured over it, but failing that, would foil-backed kingspan or similar, on the flat, be the best bet?

Or maybe attic-style wool insulation?

In either case, it is sufficient to just lay it down and spread it out or should it be overlaid with something else - maybe fixed with timber in some way?
 
Well, I'm referring to the previous conversation (in which you were v. helpful) regarding insulating under the slope of the roof of a dormer bungalow, i.e. the inaccessible area "hidden" by a stud wall....

... and I'm under the impression that insulating the top of the hollowcore (which is at the heart of the issue, I guess - if we had timber joists there'd already be insulation there) is the way to go.

SO my follow up question was just, assuming I wanted to insulate the currently UNinsulated hollowcore on the flat, what's the best material to do this with?

One additional thought: would it be an option to dryline the ceilings underneath the uninsulated hollowcore ceilings? I.e. there are habitable rooms directly underneath.

Sloping roof
over
Hollowcore
over
Downstairs room

(See diagram in original post)

Thanks!
 
to meet current regs you need to incorporate 150m of PUR (kingspan etc) or 300mm quilted insulation at the horizontal ceiling. I would personally insulate all the roof on the slope.. i dont know how practical this is for you right now, but IMHO thats the best option.
I assume the wall plate is on the hollocore slab... and that there is insulation at the edges around the conc slab...
 
sydthebeat said:
I assume the wall plate is on the hollocore slab... and that there is insulation at the edges around the conc slab...
Click to expand...
I'll have to check that, but I think so.

Drylining from underneath wouldn't be any good, then?
(Given that my real concern is the heat from the groundfloor living rooms underneath which is rising through the hollowcore ceiling and straight through the uninsulated cavity space and out the uninsulated sloping felt)


Cheers!
 
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i think the best option is to create the situation where the hollowcore slabs are 'inside' the insulation envelope.

Ive drawn up a little section to describe it better....
http://www.4shared.com/dir/4960625/6cc4047/sharing.html

check out the eaves... thats the way i would do it.....
for the following reason alone....
if you plan to use the cavity space behind the stud wall, then this construction is better. You are not compromising the insulation envelope by adding doors etc, and you retain the space over the slabs...
 
Syd, you've gone above and beyond the call of duty with that drawing, thanks so much. You're a gent.

I can fully see that is the correct way to do it and how it should have been done in the first place. Unfortunately the man who built this house seems unable to understand concept of a heat envelope and so the slope has been sealed (i.e. no access, stud walls are closed), so it would be difficult and intrusive to get in to insulate the slope now...

... which is why I was wondering about dryling from underneath. Even as a short term solution, would drylining be any good at all, do you think?
 
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in order for that section of ceiling to comply with building regulations you would have to 'dry line' with at least 150mm or rigid board insulation. this may be undesirable in the rooms below.
I would incorporate 150mm insulation over the slabs... and ensure you get insulation where the ends of the slabs meet the eaves.
 
Fantastic Syd, thanks for the info, you've clarified everything in my mind, very much appreciated.
 
Hi !

I've read a number of threads on here about insulation, but I'd really appreciate if someone can just sanity check this for me so I don't make a costly mistake.

We have a dormer house with access to the crawl spaces via doors in each of the upstairs rooms and on the landing. They were left so we could use the area for storage. If we want to do this I think we need the crawl space to be 'warm'. We have the plasterboard short dormer wall insulated at the back between the joists with fibreglass but as we are in an exposed place regardless of what we do with the doors we end up with a gale coming down the stairs to meet us.

So, I was going to put 60mm of Kingspan between the sloping roof joists in the crawl space and then seal along the bottom (where the board will rest on the cavity wall) with expanding foam or silicone. Will probably use additional fibreglass to seal the top of the board if necessary where it disappears into the sloping wall/roof section of the dormer (this has aeroboard in it - pre stricter regulations). Does this sound right ? The roof joists are 150mm deep so plenty of room at the back of the insulation for air circulation to attic.

I was thinking we would have room for 100mm Kingspan board but thought the 60mm would be easier to fit - no point in fitting it if we can't get a good fit. I was hoping the 60mm could be cut with a good knife rather than a saw ?

Anyone done this ? Advice greatly appreciated !

Thanks is advance,
R-
 
ronny - sounds like my old house. I insulated and slabbed BOTH sides of the dwarf wall........and it was still a wind-tunnel.

This is to be expected, really, as the wall/roof junction is.......wide open - it's not airtight.

What I would do is this: insulate between the rafters, in the crawl space, from the top of the dwarf wall down as far as you can (usually just past the line of where your crawlspace floor meets the rafter....).

Then, get some airtight membrane (Intello, CIGA, etc), and line the back of the rafters and onto the 'mini-gables' at the ends of those spaces, back onto your dwarf wall. Do the back of the Dwarf wall too, if you can/want to. Then, seal all the joints in the membrane with an appropriate tape (again, Intello, CIGA etc).

Almost there !

Ooops- forgot - is your crawl space floored ? If not, insulate/membrane/etc, as above. Then floor it. I sheathed the bottom of my rafters with light ply as well, inside the crawl space, so that the whole crawl space has a solid 'roof', floor and dwarf wall.

Finally, use a good draught seal on your hatch doors.
 
Hi Galwaytt - thanks for your reply.

Yes there is a floor in the crawl space and there is insulation under it between the floor joists so although we are still no doubt losing some heat from downstairs this hasn't been an issue as downstairs is very warm.

In your old house, did the outside wall of the house extend up into the crawl area ? We have about 2 feet of the concrete cavity wall all the way around. Will the Intello tape stick to the block when Im fitting the membrane over the rafters and kingspan or is this a job for silicone to keep the membrane in place ?

Thanks again,
R-
 
Kingspan/Xtratherm etc. manufacture a rafterlock type product that is 100mm/150mm and is precut to suit rafter, accordion type that you squeeze,fit between rafters, and it expands to give snug fit. A bit more expensive than 8x4 sheets but a lot less messing and waste.Should cost roughly €85 vat inc for 4.44mmtr sq bale of 100mm [broken link removed]
 
Hi Seantheman,

Thanks for your reply. That sounds like the product for me. The only thing putting me off going for the 100mm insulation was thinking that I might not get a good fit and it would end up having been a waste of money. I think I'll order a bale of that and see how I get on. I can assess any draughts at the top of the cavity wall once I've made a start on the insulation. I may end up back here again for further advice !

Thanks again,
R-
 
Ronny - there was only 1 row of blocks above the joists, at the outside of my crawlspace. SIGA airtightness tape RISAN iirc, will stick, with a primer. But you should the membrane down over the block, on to the crawlspace floor. I think SIGA have a gun-gum you could use to tack the sheet to the block as well, just to stop it falling in.
 
I have a dormer bungalow. The question is "what depth of insulation should I have in between the joices between the ground and dormer floor?
 
Coolaboy said:
I have a dormer bungalow. The question is "what depth of insulation should I have in between the joices between the ground and dormer floor?
Click to expand...

I hope I'm reading this right.

You seem to be talking about the First Floor.

No insulation here, unless your're using it for sound insulation.

Thermal insulation is only required for the "outside" of the habitable rooms, not between them.

So the lowest floor requires insulation between the rooms and the ground itself and the upper floor requires insulation between the bedrooms and the air outside.

HTH

ONQ.
 
Thats very interesting ONG. I was going to insulate between the floor joices. If I were to do this, what would be the outcome? Does it stop warm heat rising up through the ceiling into the dormer. Is that one of the reasons why?
 
It's still worth insulating the joisting out by the wall.

If you think about it, that space is usually not insulated at all - any heat that does find it's way in there will have free access to your (cold) outside walls, for the height of the joist - anything that stops that is a + in my book.
 
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