Hi All, hope I can describe this ok. I live in a 50’s semi and part of the back wall of the house juts out about 3 feet from the rest. The roof line on the bit that juts out follows the main roof line so the facia on that bit is about 18” lower that the rest. Inside the house, the bit that juts out goes across a bedroom and airing cupboard and presents a sloping ceiling on part of the room and all of the airing cupboard. Because of recent alterations where header tanks in the loft have been removed I can now see, from inside the loft, down into the gap between the roof tiles and the ceiling of the room and airing cupboard. The roofing felt is in tatters (as it is on the rest of the roof) and as I have suspected for years there is no insulation whatsoever between the roof tiles and the bedroom ceiling. I would like to tackle this lack of insulation. Suggestions have been: Try and slide some Celotex into the gap from inside the loft. Trouble with this is that because of the joist configuration I don’t get the full width at the point where I have to slide it in. I would also worry that it’s a bit hit and miss and I might snag on the way down. Do it from inside the room, possibly with plasterboard lined with Celotex and skim. This is feasible but would want to use at least 75mm Celotex so would lose nearly 100mm by the time its finished. Also do I need to leave any gaps or protect against condensation in the space? Certainly condensation forms on the ceiling in the room at the moment. Ask a roofer to remove the tiles from the outside and insert Celotex that way. Hope this reads ok. Any thoughts?
Hi Fred. When you look down that gap, it's rafters running down with the roof battens on one side and the bedroom ceiling on the other - the only gap is the thickness of the rafters? 4"? 5"? Anyways, do not shove your insulation down there! That will restrict the very necessary air-flow up that void which keeps the area dry and free from condensation. You might be able to get a thin sheet of rigid insulation down and sit it tight against the bedroom ceiling with raggedy gaps on either side, but I doubt that'll make much difference as it won't be tight, and any gap you leave could be a haven for condensation forming. So, forget that for a lark. Don't necessarily worry that your felt is in tatters - I understand it's mainly there as a secondary barrier should a tile fall off, or I've heard it can also act as a kind of wind break to hold off the worst of the air pressure betwixt inside and oot. In many ways, the old-style 'felt' was undesirable stuff as it really was wind-proof and non-breathable, and could often be seen to allow condensation to form on it because of this. So, forget about your tattered felt too . And if your roof tiles are currently ok, then you'd be nuts - nuts, I tell ye - to start taking them off to gain access to that space. NUTS! So that leave one very simple, sensible, easy, cheap and probably the most effective solution - the Thermal P'board you mentioned. But you don't need anything like 75mm or more. Whatever thickness you add will make a huge difference, and adding more will have progressively less additional effect . If you went for the thinnest you can get, which is only around 35mm total thickness (25mm insulation and 9.5mm p'board), that will transform that area. You'll only lose an inch and a half in total - nifty, eh? And all you have to do is screw it on there using extra-length p'board screws. By all means go for the thickest you can get away with, but - honestly - even 35mm is brill. I have lined a single-block-skinned external wall on what used to be an attached garage with 35mm Thermal Laminate Board, and it's a genuinely cosy room. When you think about it, 25mm high quality insulation will make a HUGE difference. Adding a further 25mm will only reduce the heat that got through the first lot, so only a tiny fraction of extra improvement. And it's a nice DIY job. (Where the low wall sheets meet the sloping roof, don't forget to mitre the sheet along that joint, including the insulation, so's the insulation is a continuous barrier all the way up and over - does that make sense...?)
Many thanks Devil's Advocate for taking the time to post this reply. I will proceed as you suggest. All the best. Fred
It's looks like I am going to struggle getting the insulated platerboard locally. Any issues with fixing the celotex and plasterboard separately?
Also ... there is a curve where the slope meets the flat ceiling, this will create a void behind the Celotex. Should I try and remove that curve - presumably its just been in filled with plaster.
No issues with using Celotex & p'board separately - in fact it might be easier to handle in this case, when you consider the curved corner. Just find and mark out where the vertical studs are first... How much of a curve is it? Just a decorative radius similar to the roundness of a mug (go fetch a mug) or far more gradual like a hoopla circumference. (It's really important to use the correct building terms.) If more like the former, then I think you'll find the 30mm Celotex (or what thickness were you thinking of?) will trim to fit in there neatly and still leave enough thickness to insulate that corner. In which case that's the easiest thing to do - the two panels of p'board will then butt sharply and give a much neater - and more modern - look. If the radius is bigger so that to trim the insulation to fit would mean it's very thin in that corner (which would be bad - you don't want that edge to be colder than the rest), then it would be best to trim that radius away; you could try using a long-bladed 'snap-off blade' craft knife and running it with blade extended and held flat against the wall with the tip starting to cut into the corner. Use the flat wall/ceiling as your guide and make long gentle cuts into the corner. Does that make sense? If it's a very slow curve, then I'm not sure - you may even have to use a flexible insulation layer and even gently pre-bend the p'board to suit. I dunno. Anyways, tell us what radius you have - mug, plate, hoola-hoop...
Thanks again Devil's Advocate, you make perfect sense. I reckon its a slow radius, went up there with a dinner plate and a side plate to find its larger than both, could be hoopla size or in between the dinner plate and a hoopla. I got a straight edge on it and estimate that the curved bit is about 10" long but I don't reckon its circular, seems to transition a bit. Will it matter if there is a small gap behind because the straight edger revealed that the flat bit isn't perfectly flat either!
Just knowing that such corners tend to be the most susceptible areas to condensation and mould forming - probably due to the lack of air circulation - would make me want to have these corners at least as well insulated as the rest of the wall. Solution? Dunno. What do others think? Any chance of a photo - taken side-on - so's we can gauge?
Photo attached. The parallel lines are my estimate of the start and finish of the curve. Its a bit less than the 10" I said above, more like 6". The mess at the end is where I have "investigated". The section of horizontal roof immediately to the left the curved bit isn't that flat but its supposed to be! I would like to insulate the sloping bit, the horizontal bit and the the vertical bit where it joins the proper ceiling. Thanks for sticking with me on this. Fred
Popped down to Wickes and spent a tenner on a bit of 9.5mm plasterboard and small bit of 50mm Celotex (cavity wall board) just to see what it looked like and test the angles etc. Constructed a cross section about 8" wide. Forgive the **** cutting and protruding screw heads, they weren't long enough to reach the rafters. But basically the attached picture is a cross section of what I would get. I chamfered the Celotex a bit to take out the curved bit of the roof and it fits ok'ish but even with better cutting I still think there would be a few gaps where the Celotex sits against the existing or the new plaster board. Any thoughts? Fred.
Nice job - there are no problems there at all. Much smaller curve than I'd imagined. You are hardly losing anything in thickness in that curve. You could get away with thinner insulation if you thought it would be easier to handle and fix, but by all means stick with the 50mm if you are happy. You are gonna need long bludy screws, tho'... I did something very similar in my own home - I think it may have been 50mm Celotex too - and couldn't find p'board screws long enough. I had to use normal wood screws, but do use those which are well rust-proofed. (I think the essential difference betwixt the two types is that p'board screws have 'bugle' heads whereas orn'ary screws are 'countersunk'. The difference? I'm guessing the 'bugle' heads have that characteristic bugle-horn curve to their profile and are designed to not tear the p'board paper skin when driven slightly below the surface. Anyone know for sure? If you want a s***-hot job, get a can of expanding foam and run a thin bead along the end of the Celotex before butting up the next piece - a perfect join
Ok, thanks Devil's Advocate. I was wondering what was special about plasterboard screws, except that they always seem to be black! Those were 5x80mm Goldscrews. They reached ok pining the Celotex up but not with the 9.5mm plasterboard too. I've just bought a foam gun so will be able to take your advice about the bead of foam. Incidentally I had overlooked Jewson and Travis Perkins and can get the combined stuff there. Still weighing up which way I would do the better job with. Just realised that with the combined stuff I will have some exposed foam on that external corner. I've resigned myself to the fact that it will almost certainly need skimming. Thanks again for your help. Fred
I think I would personally stick with using two layers as it'll be a lot easier to handle - you'll be able to trim the insulation layer to fit that curve snugly so's the sheet can sit nicely flat, and then seal it all with expanding foam to make a cracking job. Ditto with 'butting' the outside corners. Then fitting the p'board over it all will be a simple, neat job too. But, your call. If you decide to go for the combined stuff, I think I'd mitre both the inside and outside corners. With the outside corner, if you don't mitre, you'll have to trim away the thickness amount off the insulation at the joining end of the insulation so's the p'board itself can overlap and meet. Does that make sense? (If not, try a sketch ) And consider using slightly thinner Celotex if you think 50mm could be awkward to handle. But stick with it if you think it'll be ok! Our hosts do 100mm long p'board screws: http://www.screwfix.com/p/easydrive...thread-drywall-screws-4-8-x-100mm-pk250/93438 Will they be long enough? And perhaps trim fractionally more from the insulation so's it lays more flat and you lose any light curve in the final job. An extended 'snap-off blade' knife slicing at a low angle should do this fairly easily.
Yes, going to stick with the two layers, easier I think and if I mess up I can go down to Wickes and probably sort it out for a fiver. The combined stuff is an arm and a leg. Was intending to use Goldscrews simply because I don't do much plasterboarding and at least they will have a use later. Think I can get a 5x100mm that will do the job. I'll post a picture when finished but don't hold your breath - day job tomorrow!! Thanks again. Fred.
Thanks both, have to admit that we got a man in to do the plaster / plasterboard, but he thought the Celotex was a nice job. Have to admit that I'm really chuffed with it, room feels more comfortable even in this mild weather.
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