ToughButterCup Posted February 4, 2019 Share Posted February 4, 2019 I have already put 200mm of insulation between my rafters, and now I need to fix 80mm of Celotex under those rafters. Since I should be able to do that by attaching the insulation to the bottom of the rafters, I am guessing that I don't need to use thermally broken fixings. But I have been known to be wrong before - strangely. So I just thought I'd check. Anyone got a suggestion as to which fixings I should use for 80mm Celotex? Link to comment Share on other sites More sharing options...
scottishjohn Posted February 4, 2019 Share Posted February 4, 2019 (edited) then plasterboard after that? If you not bought cellotex it yet --why not 92.5mm insulted plaster board job done in one go and its simple long screws then Edited February 4, 2019 by scottishjohn Link to comment Share on other sites More sharing options...
ToughButterCup Posted February 4, 2019 Author Share Posted February 4, 2019 9 minutes ago, scottishjohn said: (...) why not 92.5mm insulted plaster board job done in one go and its simple long screws then Because I did not know that insulated plasterboard exists. The inexperienced self builder strikes again Link to comment Share on other sites More sharing options...
scottishjohn Posted February 4, 2019 Share Posted February 4, 2019 (edited) oops what ever yo do you going to need to mark all your rafters well so you can find them with the drywall fixings maybe something like this https://www.twistfix.co.uk/insulation-fixings?msclkid=41076a7a775a19e9c0c23622113a79f6&utm_source=bing&utm_medium=cpc&utm_campaign then you will need 110-120mm drywall screws for plasterboard Edited February 4, 2019 by scottishjohn Link to comment Share on other sites More sharing options...
Carrerahill Posted February 4, 2019 Share Posted February 4, 2019 20 minutes ago, recoveringacademic said: Because I did not know that insulated plasterboard exists. The inexperienced self builder strikes again Neither did I until last year, then looking at my building warrant drawings I saw "40mm insulated plasterboard" - I thought this was just poorly written and meant some insulation then PB - but no, they make it right up to about 150mm I think! So that is what I am doing my ceiling with. https://www.roofingsuperstore.co.uk/product/celotex-pl4025-insulated-plasterboard-1-2m-x-2-4m-37-5mm.html?gclid=CjwKCAiA4t_iBRApEiwAn-vt-2Se-YUgDUcezZG-USHSv1-qocyATnDPBL_jlSLNG0f6SJfaNEc3ChoCyngQAvD_BwE Link to comment Share on other sites More sharing options...
Mr Punter Posted February 4, 2019 Share Posted February 4, 2019 I think you may struggle to get drywall screws longer than 100mm. If you go down to 60mm insulation it will be far easier. Hold the insulation in place with the drywall screws plus penny washers and drive them beyond the face of the insulation. Do all the insulation first and tape the joins with alu foil tape. Make sure you carefully mark the rafter locations at the top and bottom. I prefer 15mm plasterboard. Link to comment Share on other sites More sharing options...
Declan52 Posted February 4, 2019 Share Posted February 4, 2019 I used 100mm nails to hold mine up. About 6 per sheet till I got the plasterboard up and then used 125mm plasterboard screws. But I done mine room by room so the insulation was only held on by the nails for about 3hrs till I got the plasterboard up. Link to comment Share on other sites More sharing options...
ToughButterCup Posted February 4, 2019 Author Share Posted February 4, 2019 Thanks @Mr Punter I'm using 80mm of insulation under the rafters. So, it's drywall screws and penny washers (and alu tape) I need then? Link to comment Share on other sites More sharing options...
ToughButterCup Posted February 4, 2019 Author Share Posted February 4, 2019 1 minute ago, Declan52 said: I used 100mm nails to hold mine up. About 6 per sheet till I got the plasterboard up and then used 125mm plasterboard screws. But I done mine room by room so the insulation was only held on by the nails for about 3hrs till I got the plasterboard up. Interesting..... yes @Declan52, the difference is that you know what you are doing , and I - well, dont. Did you not tape the little gaps between the sheets of insulation? Link to comment Share on other sites More sharing options...
Declan52 Posted February 4, 2019 Share Posted February 4, 2019 Yep. I bought the alu tape from Amazon and tried to use it. Think it was about half as thick as cling film and impossible to peel back. Got rolls from screwfix which where much better. As above marking the joists with a black marker is the important bit. Nails or screws is the option. They aren't there to hold it in place for ever that will be the job of the 50 odd screws you put in the plasterboard. Just make sure they don't stick out proud or you will bust the plasterboard. Link to comment Share on other sites More sharing options...
Cpd Posted February 4, 2019 Share Posted February 4, 2019 1 hour ago, recoveringacademic said: 200mm of insulation between my rafters Did you foam this in > off course you did. Marking top and bottom of the joists is essential, I then line the laser line at it to get bang on centre every time....... I am sticking 60mm under my joists in the shed so it’s a bit easier, I can only buy 100mm max length drywall screws locally. Link to comment Share on other sites More sharing options...
ToughButterCup Posted February 4, 2019 Author Share Posted February 4, 2019 2 minutes ago, Cpd said: Did you foam this in > off course you did. [...] Who's a clever boy then? I am..... Thanks about the tip to use the laser . I might have worked that out after I'd got it disastrously wrong...... Link to comment Share on other sites More sharing options...
bissoejosh Posted February 4, 2019 Share Posted February 4, 2019 Are you having a service cavity under the 80mm? Won't the battens that create this do the job of fixing the insulation / plasterboard long term - could just be long wood screws I'd have thought. Link to comment Share on other sites More sharing options...
ToughButterCup Posted February 4, 2019 Author Share Posted February 4, 2019 1 minute ago, bissoejosh said: Are you having a service cavity under the 80mm? [...] No, but only because I haven't thought about that - or even knew that you could do that. To be clear, under the joists, tack a 25mm batten (like a roofing batten) to act as a service cavity. Then attach the 80mm. Insulation to those battens, yes? That's got me thinking now..... interesting. Link to comment Share on other sites More sharing options...
Cpd Posted February 4, 2019 Share Posted February 4, 2019 3 minutes ago, bissoejosh said: could just be long wood screws I'd have thought. I have found gyprock drywall screws to be the cheapest when buying at 90mm £14.40 for 250 quality screws for sure. Link to comment Share on other sites More sharing options...
bissoejosh Posted February 4, 2019 Share Posted February 4, 2019 6 minutes ago, recoveringacademic said: No, but only because I haven't thought about that - or even knew that you could do that. To be clear, under the joists, tack a 25mm batten (like a roofing batten) to act as a service cavity. Then attach the 80mm. Insulation to those battens, yes? That's got me thinking now..... interesting. I'd do it the other way around. Insulation then batten - the screws for which could be long timber screws to sandwich the whole lot together. The other advantage is this gives a service zone for cable runs / light fittings and also a safety margin for your vapour control / airtight layer when fitting plasterboard screws. Link to comment Share on other sites More sharing options...
bissoejosh Posted February 4, 2019 Share Posted February 4, 2019 Also 280mm of PIR is quite a lot of insulation - nothing wrong with it but a thinner layer might make things easier if it can work with your SAP etc? Link to comment Share on other sites More sharing options...
Cpd Posted February 4, 2019 Share Posted February 4, 2019 Just now, bissoejosh said: Also 280mm of PIR is quite a lot of insulation - nothing wrong with it but a thinner layer might make things easier if it can work with your SAP etc? I went with 170mm between rafters and 25mm over the top.... am still tempted to add another 25mm or more onto the top...... Link to comment Share on other sites More sharing options...
bissoejosh Posted February 4, 2019 Share Posted February 4, 2019 Just now, Cpd said: I went with 170mm between rafters and 25mm over the top.... am still tempted to add another 25mm or more onto the top...... I was thinking a reduction to something like 40/50mm might make fixing easier especially if battens are added to the mix. Link to comment Share on other sites More sharing options...
Declan52 Posted February 4, 2019 Share Posted February 4, 2019 16 minutes ago, recoveringacademic said: No, but only because I haven't thought about that - or even knew that you could do that. To be clear, under the joists, tack a 25mm batten (like a roofing batten) to act as a service cavity. Then attach the 80mm. Insulation to those battens, yes? That's got me thinking now..... interesting. Insulation then the batten would mean you don't have to use long plasterboard screws. Still need long screws for the fixing of the batten though but you would use less of the longer ones plus shorter plasterboard screws so cheaper. You can have it insulated and batten then the spark can come in and do his thing. What kind of lights are you going for as these might need some timber to fix to depending on your choice. 1 Link to comment Share on other sites More sharing options...
scottishjohn Posted February 4, 2019 Share Posted February 4, 2019 1 hour ago, Cpd said: I have found gyprock drywall screws to be the cheapest when buying at 90mm £14.40 for 250 quality screws for sure. I looked when i posted before and i could find 120mm drywall no problem on ebay 1 hour ago, bissoejosh said: I'd do it the other way around. Insulation then batten - the screws for which could be long timber screws to sandwich the whole lot together. The other advantage is this gives a service zone for cable runs / light fittings and also a safety margin for your vapour control / airtight layer when fitting plasterboard screws. vcl will need to go directly to insulation then batobs then drywall or you will be cutting holes in it for lights Link to comment Share on other sites More sharing options...
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