How to go about plasterboarding an angled ceiling?

[Mark A]

We have 270mm of rockwool in the loft, but that part of the ceiling where the roof truss forms part of the ceiling is just 10mm polystyrene backed plsterboard and a 70mm or so airgap, then the roof felt and slates. So must be losing a fair bit of heat through there.

I was thinking of battening it out with 40mmx40mm timber and then putting 40mm kingspan between and plaster boarding over the top. I have 5 sheets of Kingspan I need to use up and this seems like a good way of doing it. It's still not great, but better than 10mm insulation.

My main concern is how would I go about making sure the skim doesn't end up cracking along the line where the plasterboard will meet the existing painted plaster?

TIA

 

[Mark A]

I like the sound of glueing the insulation straight to the plaster, would certainly be a lot easier. The insulation is Kingspan 40mm, with foil on both sides. Are there any products out there that will glue the insulation in place? I have loads of expanding foam or 5 minute polyurethane glue if that will do.

Or what about gluing a layer of foam onto the plasterboard and then screwing battens over the top into the joists behind and then add more insulation between the battens?

 

[Mark A]

Thanks, i'll probably get one with it this weekend. Really need to get these sheets of insulation out of the way.

 

[Mark A]

Stage 1 complete. Glued it in place with expanding foam and put some 80mm screws with washers into the timber behind.

I used rare earth magnet to locate the nails that hold the studs in place to find the studs and it worked amazingly well. I should be able to screw the plasterboard into the ceiling studs at the very top with normal 40mm drywall screws and then just use some long screws to fix it at the bottom and middle.

One question about the plastering: Will I have to sand the emulsion paint off the ceiling where the scrim tape will be joining the plasterboard to the ceiling?

 

[Mark A]

Still not got around to plaster boarding it yet due to other more pressing jobs . It's definitely made a difference though. When I was putting the sheets up I could feel the heat reflecting from the foil and with it being directly under the radiator it should help stop the heat going straight outside.

Ideally I'd have put 2 layers on there to make 80mm, but I think it might look a bit odd with a large angled ceiling area.

I'll hopefully get some time to get it plastered etc soon and i'll post some pics. Then if it turns out ok i'll do the whole of the upstairs as I still have 4 sheets of insulation that need using up.

 

[Mark A]

Completed one of the rooms today. It was my first proper go at plastering and it didnt turn out too bad. Had to do just one coat instead of two as the plaster went hard by the time i'd put the first coat on and it was too late to start mixing more. Hope this wont cause any problems. Would it be ok to add another coat tomorrow or will it be ok with 1 coat?

Its just a box bed ceiling that will be painted matt white, so doesnt need to be perfect. I started on this room despite it being the hardest, so I could practise before doing the other rooms.

 

[Mark A]

2014 it says on the bag so I think I must have just mixed it too thick. It was falling straight off the trowel at first, so i added a bit more plaster and that must have overdone it.

Actually quite enjoyed doing it once I got the hang of it. It's not a job I could do all the time, but enjoyable for some small DIY jobs. Think i'll give a full wall a go in the summer.

 

[Mark A]

Thanks, that seems about the consistency I had, so It must just be due to me taking to long to slap it on .

I'm going to tackle the other bedroom next. This one I put full sheets of insulation onto the existing plasterboard and foamed and screwed it in place. Only problem I have now is how to attach the plasterboard to the insulation.

I was thinking of getting some Soudal Fix-all polymer adhesive and glueing the plasterboard to the insulation and then putting some screws through it and into the timber behind.

I'll need 100mm screws to reach the timber. Will it be ok to use 5x100mm wood screws?

 

[Mark A]

Well no one mentioned anything like that when I made the thread. The insulation is foil on both sides, so i'd have thought this would stop any moisture getting through.

It's a bit late to do anything differently now, so will just have to see what happens. What would you suggest I should have done instead?

 

[Mark A]

http://www.zinsserdirect.co.uk/product_info.php?products_id=11

Does anyone know if you can paper over this product?

Want to seal, prime and add a barrier to stop any stains or mould coming through to the lining paper.

 

[Mark A]

I was hoping that wouldn't be the case as there is some polystyrene insulation on the back of the previous plasterboard, although It's only around 10-15mm.


I'll keep my eye on it and if I see any damp or mould i'll re-do it and remove the old plasterboard. I'll take your advice and remove the old stuff in the next room i do, but I think that's probably a job for the summer.

 

[Mark A]

Put a coat of paint on the ceiling, sanded the hip beam down, lining papered the walls and installed a blind. Looking much better if you compare with the before pics .

Still needs another couple of coats to cover up that horrible blue paint and then the walls will need a coat.

 

[Mark A]

It turned out very well, although my plastering wasn't perfect. The rooms have been noticeably warmer and heat up much quicker and not had any issues with damp or anything. Probably a good idea to follow the advice of others regarding the damp proof membrane etc, but luckily I have had no issues.

 

[Mark A]

Sorry for the delay, had to try and get them off my photobucket account that is now slow as hell to use. I think if I was doing it again i'd remove the old plasterboard and then after adding the insulationboard between the timbers i'd use some insulation backed plasterboard for the final layer. That way the timber doesn't create a cold bridge. Also the insulation backed plasterboard has a vapor barrier integrated. I think someone actually suggested this method, but after I had already done the job lol. It has been absolutely fine though doing it this way, with no damp or anything *touch wood*.

I can't believe they designed houses so poorly when this was built. Although It was a council house, so they probably just wanted to do it as cheaply as possible. I know what you mean about the corner rooms being the worst, this room was freezing before doing this. The radiators are also below the heat leaking sloped ceiling, so a lot of the heat is escaping straight through the roof.

We also had cavity wall insulation done around the same time which also made a small difference. The cavities are only thin in this house as its random stone, so they pumped in expanding foam. that has been good so far as well with no damp issues some on here warned about. The wall on the left was actually black with mold before I started and the wall paper was wet through due to the damp, but 4 years later after the insulation its dry and no mold, so its definitely worked.