Moggaman Posted November 22, 2020 Share Posted November 22, 2020 Hi all i wonder why people on new builds put insulated plasterboard on the inside of the external wall. I presume its because they do not want a wider cavity.... but if you want a certain u value shouldnt u widen the cavity to allow all the insulation to be put in there... also means you can plaster the inside wall to provide your simple finish,, am i missing something? As an aside, if in a masonry build you put all your insulation in the cavity and you plaster and skim the internal wall, how do you make electrical sockets (for instance) airtight? Also i note many masonry houses near me have 350mm cavity wall with 110mm xtratherm insulation inside... I presume a full fill cavity with PIR board is a good option Thanks Link to comment Share on other sites More sharing options...
nod Posted November 23, 2020 Share Posted November 23, 2020 I used insulated plasterboard on my external walls It’s quite uncommon to do this on a new build I’ve plastered thousands of new builds and haven’t been asked to do this As you say you can simply widen the cavity Sealing around the sockets is pretty much the same as normal I used 40 mil back boxes that left only PB showing on the inside of the box 1 Link to comment Share on other sites More sharing options...
Onoff Posted November 23, 2020 Share Posted November 23, 2020 6 minutes ago, nod said: I used 40 mil back boxes that left only PB showing on the inside of the box D'you mean 40mm or 35mm...(47mm even)? 1 Link to comment Share on other sites More sharing options...
nod Posted November 23, 2020 Share Posted November 23, 2020 47 ? 1 Link to comment Share on other sites More sharing options...
SteamyTea Posted November 23, 2020 Share Posted November 23, 2020 13 hours ago, Moggaman said: As an aside, if in a masonry build you put all your insulation in the cavity and you plaster and skim the internal wall, how do you make electrical sockets (for instance) airtight Or keep the insulation airtight for that matter. 1 Link to comment Share on other sites More sharing options...
Moggaman Posted November 23, 2020 Author Share Posted November 23, 2020 14 hours ago, nod said: I used insulated plasterboard on my external walls It’s quite uncommon to do this on a new build I’ve plastered thousands of new builds and haven’t been asked to do this As you say you can simply widen the cavity Sealing around the sockets is pretty much the same as normal I used 40 mil back boxes that left only PB showing on the inside of the box Thanks.I’m talking about behind the electrical boxes where it wouldn’t be plastered ? I presume the space for the box and cable are chased out... the cable part can be plastered over grand but behind the box can’t.just thinking in terms of airtightness Link to comment Share on other sites More sharing options...
nod Posted November 23, 2020 Share Posted November 23, 2020 16 minutes ago, Moggaman said: Thanks.I’m talking about behind the electrical boxes where it wouldn’t be plastered ? I presume the space for the box and cable are chased out... the cable part can be plastered over grand but behind the box can’t.just thinking in terms of airtightness The boxes are fixed directly to the wall Link to comment Share on other sites More sharing options...
ProDave Posted November 23, 2020 Share Posted November 23, 2020 The modern way is you do NOT put your sockets into the wall, you create a battened service void that lets you run cables inside the building envelope without disturbing it's air tightness etc and fit sockets into the plasterboard that covers those battens. So much easier to make alterations or add extra sockets. Link to comment Share on other sites More sharing options...
Moggaman Posted November 25, 2020 Author Share Posted November 25, 2020 On 23/11/2020 at 21:27, ProDave said: The modern way is you do NOT put your sockets into the wall, you create a battened service void that lets you run cables inside the building envelope without disturbing it's air tightness etc and fit sockets into the plasterboard that covers those battens. So much easier to make alterations or add extra sockets. Yes but I want to put all my insulation in the cavity and do a sand cement /skim render finish on the inside. The sand cement is my airtight layer..seems to me the service void is added cost. Where is the airtight layer in your design , a large coat.. couldn’t i parge coat the chases? Link to comment Share on other sites More sharing options...
Oz07 Posted November 25, 2020 Share Posted November 25, 2020 @joe90 Had solid plaster. Did you have chases? Link to comment Share on other sites More sharing options...
ProDave Posted November 25, 2020 Share Posted November 25, 2020 28 minutes ago, Moggaman said: Yes but I want to put all my insulation in the cavity and do a sand cement /skim render finish on the inside. The sand cement is my airtight layer..seems to me the service void is added cost. Where is the airtight layer in your design , a large coat.. couldn’t i parge coat the chases? Mine is timber frame so different, but I would never want to go back to the old ways of plaster on the hard where you are committed to getting all your switches etc exactly right so early on and if you want to change or add something it's a messy horrible job. It's one of the things I liked when I moved to Scotland where most houses are timber frame, and end to the task of chasing wires into a solid wall. Link to comment Share on other sites More sharing options...
joe90 Posted November 25, 2020 Share Posted November 25, 2020 1 minute ago, Oz07 said: @joe90 Had solid plaster. Did you have chases? yes, render then thin coat plaster, back boxes sealed to cables with silicone Link to comment Share on other sites More sharing options...
Oz07 Posted November 25, 2020 Share Posted November 25, 2020 So back boxes chopped in and capping over chases? What did you do behind the back box and behind capping? Link to comment Share on other sites More sharing options...
epsilonGreedy Posted November 25, 2020 Share Posted November 25, 2020 On 22/11/2020 at 22:41, Moggaman said: Also i note many masonry houses near me have 350mm cavity wall with 110mm xtratherm insulation inside... It is a regional thing, best practice in the wetter parts of the UK is to maintain a cavity. On 22/11/2020 at 22:41, Moggaman said: I presume a full fill cavity with PIR board is a good option Check that your brickies are ok with this. Mine wrinkled his nose at the firmer consistency of U32 cavity batts and said "I will have to open the cavity another 5mm if you want those". Link to comment Share on other sites More sharing options...
Oz07 Posted November 25, 2020 Share Posted November 25, 2020 Which in bricklayer speak becomes a quarter of a inch, obviously then meaning half an inch wider! 1 Link to comment Share on other sites More sharing options...
joe90 Posted November 25, 2020 Share Posted November 25, 2020 My builder questioned full fill cavity (rockwall batt) but I showed him the BBA certificate fir full fill material and he cracked on. Link to comment Share on other sites More sharing options...
Seeoda Posted January 12, 2021 Share Posted January 12, 2021 Insulated plasterboard is recommended on window reveals on new houses and retrofits as far as I know. Link to comment Share on other sites More sharing options...
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