Moggaman Posted November 29, 2019 Share Posted November 29, 2019 I did some U Value Calcs and its seems that the PIR Board Insulation like CavityTherm or Xthratherm is the best option (In theory). With a thermal conductivity of 0.033 ish for bead, u would need to go to 200mm wide to make up the difference. What worries me though is that I read an article this evening saying that if the boards are not flush with the inner leaf, that the effectiveness of the insulation is reduced MASSIVELY.... I think a 5mm gaps is allowed. I am not in the house building area but I was wondering for those of u out there that watch insulation boards get installed regularly...is it possible to get them done near perfectly?. The issue i believe if they are not is that thermal loops will occur and suck the heat from inside out... Also on a slightly different note, I saw a post by someone condemning insulated plasterboard on the inside face of the external wall. I thought there was only positive with that stuff but maybe there isnt...hanging stuff for example...will chasing for wires reduce the effectiveness.. Lots of questions ... Thanks Link to comment Share on other sites More sharing options...
PeterW Posted November 29, 2019 Share Posted November 29, 2019 First question is what is your target uValue ..?? I’ve used bead at 150mm with a 25mm PIR lining and standard plasterboard and got a really good airtight finish and thermal performance. I’m not keen on cavity boards due to getting them “perfect” and unless you want to pay more per square metre on your blockwork and brickwork, you may not be happy with the results. Link to comment Share on other sites More sharing options...
nod Posted November 29, 2019 Share Posted November 29, 2019 4 hours ago, Moggaman said: I did some U Value Calcs and its seems that the PIR Board Insulation like CavityTherm or Xthratherm is the best option (In theory). With a thermal conductivity of 0.033 ish for bead, u would need to go to 200mm wide to make up the difference. What worries me though is that I read an article this evening saying that if the boards are not flush with the inner leaf, that the effectiveness of the insulation is reduced MASSIVELY.... I think a 5mm gaps is allowed. I am not in the house building area but I was wondering for those of u out there that watch insulation boards get installed regularly...is it possible to get them done near perfectly?. The issue i believe if they are not is that thermal loops will occur and suck the heat from inside out... Also on a slightly different note, I saw a post by someone condemning insulated plasterboard on the inside face of the external wall. I thought there was only positive with that stuff but maybe there isnt...hanging stuff for example...will chasing for wires reduce the effectiveness.. Lots of questions ... Thanks Insulated PB If you can afford the cost and loose a little bit off each room Regardless of what you have in the cavity you will not get a warmer feeling room than with insulated PB In my business I use miles of the stuff When everything is painted out you only have to put your hand on the wall or ceiling to tell the difference Even in a un heated building you can immediately tell which rooms have insulted PB Link to comment Share on other sites More sharing options...
Onoff Posted November 29, 2019 Share Posted November 29, 2019 54 minutes ago, nod said: Insulated PB If you can afford the cost and loose a little bit off each room Regardless of what you have in the cavity you will not get a warmer feeling room than with insulated PB In my business I use miles of the stuff When everything is painted out you only have to put your hand on the wall or ceiling to tell the difference Even in a un heated building you can immediately tell which rooms have insulted PB Do you just dot and dab it on, no mechanical fixings? Link to comment Share on other sites More sharing options...
SteamyTea Posted November 29, 2019 Share Posted November 29, 2019 2 hours ago, Onoff said: Do you just dot and dab it on, no mechanical fixings? I have seen it used on a loft conversion where it was screwed. Could see nearly every screw because the plaster skim had popped out. Link to comment Share on other sites More sharing options...
nod Posted November 29, 2019 Share Posted November 29, 2019 3 hours ago, Onoff said: Do you just dot and dab it on, no mechanical fixings? You can fix on Framing or simply Dot and dab They are great for D&D as they are so ridged We often DD 120 mil insulated boards on exposed gables Or onto Gypliner on single skin masonry Link to comment Share on other sites More sharing options...
Moggaman Posted November 30, 2019 Author Share Posted November 30, 2019 20 hours ago, PeterW said: First question is what is your target uValue ..?? I’ve used bead at 150mm with a 25mm PIR lining and standard plasterboard and got a really good airtight finish and thermal performance. I’m not keen on cavity boards due to getting them “perfect” and unless you want to pay more per square metre on your blockwork and brickwork, you may not be happy with the results. U value of 0.15 perhaps. What u value did u achieve and can I ask did u fix 25 pir to inside of inner leaf.... isn’t that just the same as insulated plasterboard... people are suggesting they dew point may be an issue with this design? Link to comment Share on other sites More sharing options...
Onoff Posted November 30, 2019 Share Posted November 30, 2019 22 hours ago, Sensus said: and that you will have a thermal bridge at intermediate floor levels. Is that through the joist ends? Link to comment Share on other sites More sharing options...
MikeGrahamT21 Posted December 2, 2019 Share Posted December 2, 2019 On 30/11/2019 at 00:18, Moggaman said: U value of 0.15 perhaps. What u value did u achieve and can I ask did u fix 25 pir to inside of inner leaf.... isn’t that just the same as insulated plasterboard... people are suggesting they dew point may be an issue with this design? I would say 0.15U target will be a cause for concern on the structure of the building, needs calculating very carefully to avoid any risk of condensation. Do you have any option to do External Wall Insulation? Link to comment Share on other sites More sharing options...
Moggaman Posted December 4, 2019 Author Share Posted December 4, 2019 On 02/12/2019 at 14:09, MikeGrahamT21 said: I would say 0.15U target will be a cause for concern on the structure of the building, needs calculating very carefully to avoid any risk of condensation. Do you have any option to do External Wall Insulation? i dont trust external wall plaster on insulation long term. i trust sand/cement render. Could you explain your comment a bit more for me please... risk of condensation if.......i run pir inside the internal leaf or if i have pir in the cavity alone? Link to comment Share on other sites More sharing options...
MikeGrahamT21 Posted December 5, 2019 Share Posted December 5, 2019 If the PIR is on the inside it will lower the temperature of the masonry and make it more likely to suffer from condensation, which could lead to serious structural issues if left unchecked. IWI tends to come with detailing for a vapour control membrane, but even then if it ever gets damaged, you could end up in trouble. Its all about the dew point within the structure, IWI moves the dew point further inside, EWI moves it further out. If you have PIR in the cavity I would imagine IWI is probably not a good idea, and EWI would be pointless since cavity PIR always comes with a cavity gap. Most people opt for EWI as you can also then use the masonry as thermal mass to help balance temperatures across the year. Sand/Cement render is very old school, thin coat render systems are very good at their jobs and if applied correctly they will last a long time, much longer than sand/cement render. 2 Link to comment Share on other sites More sharing options...
SteamyTea Posted December 5, 2019 Share Posted December 5, 2019 1 hour ago, MikeGrahamT21 said: thermal mass to help balance temperatures across the year. Oh dear, this may cause some disagreement. Link to comment Share on other sites More sharing options...
Onoff Posted December 5, 2019 Share Posted December 5, 2019 1 hour ago, MikeGrahamT21 said: thermal mass He said the "word"! ? Link to comment Share on other sites More sharing options...
MikeGrahamT21 Posted December 5, 2019 Share Posted December 5, 2019 lol, sorry, I thought the same when I wrote it. Maybe heat storage capacity is a better phrase? ? Link to comment Share on other sites More sharing options...
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