How to insulate behind sloping ceiling?

portuguesejohn · 30 Mar 2020

All rooms upstairs have a sloping ceiling and these sections of the loft are lacking in insulation.

Not much of an issue anywhere besides the bathroom, where the shower head is sitting directly below the sloping ceiling! Even though we always leave the window open during and after showering, it's eating away at the paint and causing damage. I will do the best job I can in terms of painting with moisture resistant materials and whatnot, but I think the real problem is in the loft...

Access to these areas in the loft is hard, but doable with an extendable arm or something of the like... Should I try to get some insulation roll down there? Insulation board? Anything I should worry about in terms of ventilation?

Picture provided shows the affected area that is missing insulation altogether. As you can see, hard to reach, but doable if one doesn't mind getting dirty... Will be impossible to cover everything nice and neatly, but I am trying to avoid gutting away at the bathroom as that is a cost I can't support right now!

portuguesejohn · 30 Mar 2020

Better picture attached.

No insulation whatsoever, just lathe&plaster, open space and roof!

This the shower corner as well, most of the other sections have some styrofoam wedged in!

JohnD · 30 Mar 2020

you can slide a piece of insulation slab down between the timbers, it will be difficult to fit to a close fit. I think quilt will jam unless you slide a flat smooth board down first.

portuguesejohn · 30 Mar 2020

JohnD said:
you can slide a piece of insulation slab down between the timbers, it will be difficult to fit to a close fit. I think quilt will jam unless you slide a flat smooth board down first.

Thanks for the feedback! Is that slab material easy to cut in? I assume it's a bit more solid than the typical "role" material?

What is your view on this sort of solution? https://www.diynot.com/diy/threads/insulate-sloping-ceiling-from-loft.491007/

JohnD · 30 Mar 2020

cut it with a breadknife or a fine panel saw. It sheds crumbs and dust

portuguesejohn · 30 Mar 2020

JohnD said:
cut it with a breadknife or a fine panel saw. It sheds crumbs and dust

Would something like this do the trick? https://www.wickes.co.uk/Knauf-Insulation-Earthwool-Dritherm-Cavity-Slab-37-Standard-100mm/p/113735

Hard to find anything in these plagueish days.

foxhole · 30 Mar 2020

Needs extractor fan , opening a window is very poor solution to condensation .

catlad · 1 Apr 2020

The insulation needs to go on the inside of the bathroom and then finished with foil back plasterboard and skimmed. Anything else is futile in my opinion.

garyo · 2 Apr 2020

portuguesejohn said:
Anything I should worry about in terms of ventilation?

You just need to satisfy yourself that whatever you do the roof timbers in that space are still adequately ventilated.

This could be as simple as establishing that you have a breathable roofing felt, or only filling half of the gap so leaving 50mm vent space. It's a pig of a job. If you have the head room in the bathroom and can cope with the decorative upheaval I'd overboard with a continuous slab of PIR.

garyo · 2 Apr 2020

portuguesejohn said:
This the shower corner as well, most of the other sections have some styrofoam wedged in!

I have some similar sections in my house. The ceiling joists mean that any PIR you can get down will be 50mm too narrow. I made an extension for a foam gun so that I could seal the pieces in place.

Another idea is to cut your PIR slab into a pair of sliding wedges so that you can get them through the hole and then englrge them to but up against the rafter .

portuguesejohn · 2 Apr 2020

garyo said:
I have some similar sections in my house. The ceiling joists mean that any PIR you can get down will be 50mm too narrow. I made an extension for a foam gun so that I could seal the pieces in place.

Another idea is to cut your PIR slab into a pair of sliding wedges so that you can get them through the hole and then englrge them to but up against the rafter .

This is what I am thinking of doing.

Might need to wait for this virus mess to be over with, can't seem to find much online right now that isn't 100mm thick, which I think might be a bit too much and not leave enough of a gap.

garyo · 2 Apr 2020

portuguesejohn said:
Might need to wait for this virus mess to be over with, can't seem to find much online right now that isn't 100mm thick, which I think might be a bit too much and not leave enough of a gap.

I had nice flat plasterboard to rest the PIR on. You'll have to find a way to ensure that air can't flow between the back of your ceiling and and the PIR, rendering the PIR pointless.

portuguesejohn · 2 Apr 2020

garyo said:
I had nice flat plasterboard to rest the PIR on. You'll have to find a way to ensure that air can't flow between the back of your ceiling and and the PIR, rendering the PIR pointless.

Yeah, it's an absolute headache. Maybe a thin base layer of normal wool like insulation? (the sort of material present in the rest of the loft). Try to work some foil in there?...

Makes me want to go around knocking on neighbours doors and ask how they dealt with it. Oh wait, social distancing

.

portuguesejohn · 2 Apr 2020

I will definitely be tackling this the right away once we redecorate the bathroom: Have the old lathe and plaster removed and put proper insulated plasterboard, combined with an actual extractor fan.

Until then, it's half ass insulation, good quality paint and wipe downs with an extra towel...

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How to insulate behind sloping ceiling?

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