Thorfun Posted February 17, 2022 Share Posted February 17, 2022 Hi all, I'm not far off starting our internal PIR insulation and have a quick question as to what's the best way to install it against the windows, flush or a gap? e.g. Flush: a gap: obviously, flush reduces the cold bridge but after adding AVCL and tape and plasterboard and a skim would that take a stupid amount off the profile of the window? whereas by leaving a gap for the plasterboard to sit would allow more of the window frame profile to be visible. or is there a better way? or is it simply personal choice as to how much window frame you want showing? any advice is greatly appreciated. Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2022 Share Posted February 17, 2022 Don't think there's anything in it ( though I'm sure someone will disagree ). I just left the gap. Foam filled. Then PB over it ; so more frame is visible - which I think personally is better. 1 Link to comment Share on other sites More sharing options...
Thorfun Posted February 17, 2022 Author Share Posted February 17, 2022 3 minutes ago, pocster said: Don't think there's anything in it ( though I'm sure someone will disagree ). I just left the gap. Foam filled. Then PB over it ; so more frame is visible - which I think personally is better. cheers. I thought it might come down to personal preference so I'll ask SWMBO. don't want to end up like @Adsibob and I presume it's ok to screw PB into the side of the PIR? it's not like it's going to split like screwing in to the end grain on wood? 1 Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2022 Share Posted February 17, 2022 28 minutes ago, Thorfun said: cheers. I thought it might come down to personal preference so I'll ask SWMBO. don't want to end up like @Adsibob and I presume it's ok to screw PB into the side of the PIR? it's not like it's going to split like screwing in to the end grain on wood? Your photo did confuse me . I couldn’t work out what the pb fixes too - couldn’t see any timber stud … Link to comment Share on other sites More sharing options...
Chanmenie Posted February 17, 2022 Share Posted February 17, 2022 9 minutes ago, pocster said: Your photo did confuse me . I couldn’t work out what the pb fixes too - couldn’t see any timber stud … Yeah that’s what I was thinking can you actually just screw the plasterboard to the insulation ? Link to comment Share on other sites More sharing options...
Mr Punter Posted February 17, 2022 Share Posted February 17, 2022 Do it flush. Foam the window first. The weak point is where the frame and wall meet and if you cover some of that with insulation it will help reduce the cold bridge. Protect the frame with tape and cut and remove it after plastering / painting. 1 Link to comment Share on other sites More sharing options...
Thorfun Posted February 17, 2022 Author Share Posted February 17, 2022 10 minutes ago, Chanmenie said: Yeah that’s what I was thinking can you actually just screw the plasterboard to the insulation ? yeah. sorry. on the front of the PIR will be AVCL and service cavity with battens. but I'm not sure about on the side? how does one attach plasterboard to the PIR there? Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2022 Share Posted February 17, 2022 10 minutes ago, Chanmenie said: Yeah that’s what I was thinking can you actually just screw the plasterboard to the insulation ? You can glue pir to pb . But then is the pir glued to timber frame ???? Anything like this my pb is always screwed to timber …. Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2022 Share Posted February 17, 2022 1 minute ago, Thorfun said: yeah. sorry. on the front of the PIR will be AVCL and service cavity with battens. but I'm not sure about on the side? how does one attach plasterboard to the PIR there? Really want a Batton on the window frame edge so pb can fix from there to corner batton . Link to comment Share on other sites More sharing options...
Thorfun Posted February 17, 2022 Author Share Posted February 17, 2022 14 minutes ago, pocster said: Really want a Batton on the window frame edge so pb can fix from there to corner batton . summin' like this? as is at the moment: with a 25mm x 50mm batten: with PIR: I could then add some 25mm PIR between that batten and the corner batten like this? 1 Link to comment Share on other sites More sharing options...
Thorfun Posted February 17, 2022 Author Share Posted February 17, 2022 still a bit of a cold bridge there though through the timber frame stud, into the batten and then in to the house. but I guess there'll be AVCL on top of that all anyway so I wonder how much of an impact that bridge will have Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2022 Share Posted February 17, 2022 (edited) 3 minutes ago, Thorfun said: still a bit of a cold bridge there though through the timber frame stud, into the batten and then in to the house. but I guess there'll be AVCL on top of that all anyway so I wonder how much of an impact that bridge will have Yeah . But how much ‘heat ‘ are you going to loose across that bridge ? My SE wanted ‘special ‘ bolts for some galvanised brackets to prevent a thermal bridge . The bolts were expensive. I argued if we had a 1000 then maybe . But for 20 ? . The heat transfer/loss must be minimal . Far more important in the big things like insulation in the roof and walls is installed well . Edited February 17, 2022 by pocster 1 Link to comment Share on other sites More sharing options...
Thorfun Posted February 17, 2022 Author Share Posted February 17, 2022 Just now, pocster said: Yeah . But how much ‘heat ‘ are you going to loose across that bridge ? My SE wanted ‘special ‘ bolts for some galvanised brackets to prevent a thermal bridge . The bolts were expensive. I argued if we had a 1000 then maybe . But for 20 ? . The heat transfer/loss must be minimal . Far more important in the big things like insulation in the roof and walls is installed well . yep. and timber isn't a bad insulator anyway. 1 Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2022 Share Posted February 17, 2022 3 minutes ago, Thorfun said: yep. and timber isn't a bad insulator anyway. What’s your pir build up for underground and above ground timber frame ? Link to comment Share on other sites More sharing options...
Thorfun Posted February 17, 2022 Author Share Posted February 17, 2022 Just now, pocster said: What’s your pir build up for underground and above ground timber frame ? are we playing basement top trumps again? ? 200mm EPS below basement slab with 25mm PIR on top of slab under the screed and 200mm EPS outside basement walls. for areas above ground that don't have the basement underneath we have 300mm EPS under slab. 140mm Frametherm 32 between the studs and 80mm PIR inside the studs. Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2022 Share Posted February 17, 2022 (edited) 10 minutes ago, Thorfun said: are we playing basement top trumps again? ? 200mm EPS below basement slab with 25mm PIR on top of slab under the screed and 200mm EPS outside basement walls. for areas above ground that don't have the basement underneath we have 300mm EPS under slab. 140mm Frametherm 32 between the studs and 80mm PIR inside the studs. ? Just wondering ?? I’ve got 150mm pir outside basement timber frame . 150mm pir outside . 50mm pir inside timber stud . 150mm between roof rafters . 50mm all over it ( taped ) You got ufh ? . All I’m saying is with that make up above that I have - the heat loss is low . Not a technical analysis but just from living in it . We still have an opening in the structure for cables etc . - so a draught . Yet by limited testing ( I.e turning heating off ) will take 5 hours to drop 1 degree . Edited February 17, 2022 by pocster Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2022 Share Posted February 17, 2022 8 minutes ago, Thorfun said: 200mm EPS below basement slab with 25mm PIR on top How were you allowed this ? . My problem was the compressive strength ( that pir doesn’t have ) . So we have 300mm eps below slab . Link to comment Share on other sites More sharing options...
Thorfun Posted February 17, 2022 Author Share Posted February 17, 2022 4 minutes ago, pocster said: How were you allowed this ? . My problem was the compressive strength ( that pir doesn’t have ) . So we have 300mm eps below slab . it's EPS300. our SE said the thickness didn't matter as long as it was EPS300. so I did the calculations and decided that 300mm EPS just gave a stupidly low U-value and the 200mm was sufficient for our needs so decided to save some money. the PIR was just something to staple the UFH pipes to! it was cheaper to use that than to pay for more screed and click tracks for the UFH pipes. 8 minutes ago, pocster said: 150mm between roof rafters . 50mm all over it ( taped ) You got ufh ? . All I’m saying is with that make up above that I have - the heat loss is low . Not a technical analysis but just from living in it . We still have an opening in the structure for cables etc . - so a draught . Yet by limited testing ( I.e turning heating off ) will take 5 hours to drop 1 degree . we're going for 190mm Frametherm 32 between the rafters and 100mm PIR (maybe 90mm, I will revisit those calculations in due course) below the rafters. UFH on the ground floor and basement but don't ever anticipate using the UFH in the basement. I am really not worried about heat loss tbh, but I see a thermal bridge and try and resolve the issue. the curse of a mind that troubleshoots for a living! pi$$es the wife off no end as every time she talks to me about something I have to find a solution to it. 1 Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2022 Share Posted February 17, 2022 1 minute ago, Thorfun said: UFH on the ground floor and basement but don't ever anticipate using the UFH in the basement I reckon with no heating anywhere on ; the basement is usually 3 degrees warmer than upstairs. 3 degrees just from being below ground level is a lot I reckon . No wind chill factor . My sump at this level has never had icy water even though above ground snow and ice . We should all live underground ?? 1 Link to comment Share on other sites More sharing options...
nod Posted February 17, 2022 Share Posted February 17, 2022 1 hour ago, Chanmenie said: Yeah that’s what I was thinking can you actually just screw the plasterboard to the insulation ? He will have to stick the pb to the insulation Screwing it wont work 1 Link to comment Share on other sites More sharing options...
Thorfun Posted February 17, 2022 Author Share Posted February 17, 2022 3 hours ago, nod said: He will have to stick the pb to the insulation Screwing it wont work thanks for this alternative option @nod! but it has raised a few extra questions. 1. how thick would the adhesive need to be? i.e. how much more of the frame would be 'lost' by sticking the PB on? 2. what would your preference be if you turned up to a job? the batten solution that @pocster used or the flush PIR and sticking the PB? 3. what adhesive would be best in this situation to use when considering that there will be an AVCL on top of the PIR so the PB will actually be sticking to that? Link to comment Share on other sites More sharing options...
nod Posted February 18, 2022 Share Posted February 18, 2022 I normally use Two lines of gypsum acoustic sealant Cut the nozzle 15 mil down to give 8 mil bead If your tight for space you can use 5 mil plasterboard 1 Link to comment Share on other sites More sharing options...
Thorfun Posted February 18, 2022 Author Share Posted February 18, 2022 1 hour ago, nod said: I normally use Two lines of gypsum acoustic sealant Cut the nozzle 15 mil down to give 8 mil bead If your tight for space you can use 5 mil plasterboard cheers @nod. great info as usual. Link to comment Share on other sites More sharing options...
nod Posted February 18, 2022 Share Posted February 18, 2022 1 hour ago, Thorfun said: cheers @nod. great info as usual. Your more than welcome Anytime Link to comment Share on other sites More sharing options...
Thorfun Posted February 22, 2022 Author Share Posted February 22, 2022 ended up doing this room flush to the windows. tbh it wasn't a conscious decision I just realised that by the time I'd finished it I'd forgotten that I could've put battens! sorry @pocster. think I'll just do the same throughout now. save me a lot of time and faff adding extra battens especially as the majority of my windows are 2.1m high. 1 Link to comment Share on other sites More sharing options...
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