rafter insulation with little rebuild?

[chasfromnorfolk]

Stoozy's current "best way to insulate a flat dormer.." goes a long way to answer this, I fear, but with winter fast approaching, has anyone found a neat way to introduce at least some insulation to a chilly 'room in the roof'?

My very old cottage bedrooms have about 3 feet of wall front and back (9inch brick, I could insulate that, but the lid's more important I figure) and then 50% of the ceiling is flat (insulated with about 8 inches of fibre mat) but 50% is on the slope - the underside of the rafters, front and back, the length of each room and about 5 feet wide and uninsulated.

There's not really enough working room up there in the loft to poke mat or Celotex down between rafters and in any case there's so much stuff to catch on  - plus it seems from what I've read preserving ventilation is important. The space between plasterboard and tiles is the thickness of the rafters - about 5 inches. There almost certainly isn't any felt. There doesn't seem much point in adding more fibreglass to the flat bit when the slopes are glacial.

Insulating from below would involve more plasterboard and consequent weight. Taking down the ceilings or re-roofing just isn't an option.

I had thought of bulk-buying large cans of fillerfoam to be squirted through small holes at intervals on the basis that even if I only filled half of it (to preserve some ventilation) it would as least be 50% insulated - but would that cause bulges and escape through any gappy pantiles?

Chas

[Moxi]

Hi Chas,

This has been topical on the forum recently and I got some good guidance from Biff (who will no doubt advise you later) about insulating my Skeiling (the sloping bit)

I'm going to glue and screw Kinsgspan to the existing ceiling and then fair off the screw heads with filler, sand flat and then paint, like you i need a quick win in the bedrooms upstairs before winter, if i get chance I will also start to internally insulate my 3ft walls with kingspan following the advice in some excellent threads in the forum.

moxi

[chasfromnorfolk]

Thanks for that, moxi - I went through the first 14 of the 28 pages, honestly. Probably missed a ref to skeiling!

I'll hunt down some threads, but in the meantime, what thickness of Kingspan (something else I need to research) was advised and where did you get it?

Chas

[A.L.]

hello both,

I'm going to glue and screw Kinsgspan to the existing ceiling and then fair off the screw heads with filler, sand flat and then paint, like you i need a quick win in the bedrooms upstairs before winter, if i get chance I will also start to internally insulate my 3ft walls with kingspan following the advice in some excellent threads in the forum.

moxi, I have concerns about the fire resistance if this is an occupied room

[Moxi]

The thickness is very particular to your personal circumstances and the way you intend to fit it eg air gap behined etc.  The threads and Biff, wookey and greenbeast and others will all advise you when you can give more details.

I can fit up to a 100 mm and still see the "period feature" beam although 75 mm would be more asthetically pleasing - I read several times that both celotex and kingspan are efficient and a rule of thumb is that they are both equivelent to double the mineral wool insulation equivelent thus 100mm kingspan is the same insulation as 200mm of mineral wool 75mm = 150mm

Hope that helps

Moxi

[Moxi]

Hi AL

Can we go to my thread (Skeiling) to discuss please as i don't want to hijack Chas'

Thanks Moxi

[chasfromnorfolk]

hi again moxi.
            al has a good point so you can use kingspan with the plasterboard already attached to it and follow the same procedure,
                                                                                                         biff

Don't want to divert or duplicate, so I'll follow moxi's thread to see where it leads, but I'd already discounted a full reline with insulated plasterboard on grounds of cost, weight and finish - it'll need skimming all over as I don't think the lightest 9mm boards are tapered-edge and that's beyond my diy skills...

Chas

[biff]

actually chas,
              the boards with the tapered edge and the tape are a genuine doddle to get right,really easy. you need a plasterers trowel but if you are planning a lot of diy along these lines a little practise in a hidden spot will get u up and running, the tape is to keep the joint from cracking when it drys out.,,,,,,,biff

[chasfromnorfolk]

Do you mean the thin - 3/8th in old money - boards are available tapered-edge, Biff? I thought only the 1/2 inch ones were... hence my thing about having to skim: if I was going down the reline route I could only imagine using 3/8th, (additional weight hanging on the rafters and the fag of getting the things upstairs in the first place) but couldn't (probably) give a competent skim coat all over and this is a job I have to do myself due to financial cramp.

That said, I noticed when I actually read the instructions on the plaster bag last time I used some that you're supposed to feather out the fill about a foot each side of the joins. If you can feather out two feet wide, you can probably plaster the lot!

However, all this is not, frankly, the solution I was hoping for. Is squirting the magic filler-foam really a non-starter? Energy-saving takes many forms...

Chas

[biff]

yes you can get the thin sheet with the tapered edge, not all the builders yards stock them because they are easily damaged, you would be better using the foil backed plasterboard as well, get the sheets upstairs into the room before you start,  good luck.
                                                                             biff

[wookey]

I don't think squirting foam into the skeiling space above the plasterboard will work, unless you first fit some kind of fairly rigid airway preserver. There is no way you'll get the foam to not-fill the airspace whilst also filling the insulation space without something to physically encourage it when you can't see what you are doing. If you want to fill that space rather than add extra insulation below the skeiling then you'll have to take the plasterboard off. This really isn't difficult, and may not even be terribly messy if done carefully. I know it seems like a big step to pull off nicely painted platerboard, but once you put it back and caulk and paint it again then obviously you won't be able to tell the difference.

If you are determined not to remove the pboard then you've either got to:
1) shove something down the rafter gap (needs to be rigid board, and the longer the slot the harder it is. I did mine this way (approx 0.9m lengths) but it was a right game and you can't foam up edges to seal things well.
2) Add insulation below (see moxi's skeiling thread for details).

If I was doing this again I'd pull all the plasterboard off and do it properly with a vapour barrier, some insulation between the rafters and some below to minimise thermal bridging. I'd also take the opportunity of access to stop the wind blowing out of the top of the cavity.

[chasfromnorfolk]

Thanks, all, for the contributions... much pondering to be done.

It did call to mind a very old friend of mine from 50 years ago insulating his bedroom ceiling with layers of egg trays - he had the village caff. It was warmer, but rapidly became a haven for mice.

Chas