R1plusR2 Posted April 3, 2021 Share Posted April 3, 2021 (edited) Hi all I have a floor buildup plan that my afchitect has specced out for us. I have attached a screenshot of the floor buildup. I have been prepping the floor for concrete the last two days and i just cant let it go that it seems off. To me it seems an odd design but maybe its just "different". The buildup is Screed 75mm pir but we have decided on 100. 1200g dpm 100mm **concrete base* Mot1 Sand/hardcore sub base If you noticed the buildup wording is different to the detail drawing, it clearly shows dpm on top of concrete. I have flowed screed planned for the finish rather than sand/cement. He also advised a dpm to protect the celotex but wasnt 'required' My concerns, Firstly is the dpm in the right place as most seem to be under the concrete? Second, if we dump concrete straight over the hardcore wont it dry out too fast due to the ground wicking the water out the mix too fast usually the dpm would retain the water I do have some other questions but id like to clear this up first to put my mind to rest Edited April 3, 2021 by R1plusR2 Buildup typo Link to comment Share on other sites More sharing options...
PeterW Posted April 3, 2021 Share Posted April 3, 2021 What do you think is missing as both his text and drawing show a 100mm concrete layer ..? Yours doesn’t ..? Link to comment Share on other sites More sharing options...
R1plusR2 Posted April 3, 2021 Author Share Posted April 3, 2021 Hi peter, Sorry thats a typo in my first post, il edit that. My main question is, is it normal to have a dpm on top of concrete rather than under it? Theres no dpm under the concrete on the drawing Link to comment Share on other sites More sharing options...
PeterW Posted April 3, 2021 Share Posted April 3, 2021 Doesn’t really matter. As long as it ties together then it’s fine. If you’re using a flow screed though, add another slip membrane above the insulation to stop the screed flowing down between the insulation sheets. 1 Link to comment Share on other sites More sharing options...
ETC Posted April 3, 2021 Share Posted April 3, 2021 What about a VCL? 1 Link to comment Share on other sites More sharing options...
ADLIan Posted April 3, 2021 Share Posted April 3, 2021 Would normally expect dpm below insulation /slab with vcl/slip layer between insulation and screed. Check MIs and BBA cert 1 Link to comment Share on other sites More sharing options...
R1plusR2 Posted April 3, 2021 Author Share Posted April 3, 2021 Right so its an accepted method. He did advise the secondary membrane to seperate the screed from the insulation. Thats put my mind to rest then. What about slapping the concrete onto the mot1, should i stick some dpm down just to stop the mix drying out too quick? Link to comment Share on other sites More sharing options...
ETC Posted April 3, 2021 Share Posted April 3, 2021 Radon? Link to comment Share on other sites More sharing options...
ETC Posted April 3, 2021 Share Posted April 3, 2021 Perimeter insulation? Link to comment Share on other sites More sharing options...
R1plusR2 Posted April 3, 2021 Author Share Posted April 3, 2021 Hi ETC. Are you saying a radon barrier should of been specced? Perimiter insulation is on the detail and wont be missed. Link to comment Share on other sites More sharing options...
ETC Posted April 3, 2021 Share Posted April 3, 2021 Not necessarily. Depends if you are an area where radon protection is required which I’m sure your architect has checked out. You may wish to check out the Accredited Construction Details. Looking at the detail - it looks fine. As other posters have pointed out the DPM can either go above or below the slab (below if there is a risk of the hardcore being contaminated) as long as the DPM is overlapped and continuous with all wall DPCs. Having said that I would normally expect to see a DPM above the slab/below the floor insulation overlapped and continuous with all wall DPCs, perimeter insulation and a VCL above the floor insulation. PS - Have faith in your architect. If in doubt ask him/her and raise your concerns. You are after all the client and paying fees. 1 Link to comment Share on other sites More sharing options...
R1plusR2 Posted April 3, 2021 Author Share Posted April 3, 2021 Thanks for the reply ETC. I did ask to be fair. Its mostly because i have found other things in the plans were incorrect previously, they were minor things and got corrected. But naturally i tend to look everything up and sometimes thats not a good thing but ey ho, i have ocd and cant help it! Thanks all Link to comment Share on other sites More sharing options...
tonyshouse Posted April 4, 2021 Share Posted April 4, 2021 I always built insulated floors with the membrane on top of the insulation, warm side, acts as a combined dpm/vb then - never had a problem except with occasional building inspector 1 Link to comment Share on other sites More sharing options...
Oz07 Posted April 4, 2021 Share Posted April 4, 2021 8 hours ago, R1plusR2 said: What about slapping the concrete onto the mot1, should i stick some dpm down just to stop the mix drying out too quick? Yes. I'd move it below the slab 2 Link to comment Share on other sites More sharing options...
ETC Posted April 4, 2021 Share Posted April 4, 2021 1 hour ago, tonyshouse said: I always built insulated floors with the membrane on top of the insulation, warm side, acts as a combined dpm/vb then - never had a problem except with occasional building inspector Just make sure the DPM and all DPCs are continuous. Difficult to do if the (internal wall) DPC is at slab level. 1 Link to comment Share on other sites More sharing options...
Conor Posted April 4, 2021 Share Posted April 4, 2021 Over here, the DPM normally goes on top of the concrete slab and under the insualtion. 100mm PIR isn't very much, and I'm worried that your architect only specified 75mm. What's their insualtion / cold bridging / airtightness strategy for the rest of the build??? What's your predicted SAP? Link to comment Share on other sites More sharing options...
R1plusR2 Posted April 4, 2021 Author Share Posted April 4, 2021 (edited) 75mm is the minimum requirment. we upped to 100mm due tomaking up some height id made sense to use insulation. On the extension side the dpm can and will be taped into the dpm, but we will have an issue on the old side as ETC pointed out due to inner dpc on the old side of the house being lower and slate. We was advised to just bring it up thr wall on this side. I dont know much about sap cslcs other than we didnt need them due to the glazing being kept to a standard, or at least thats how it was explained to me. I only know this because i innitially wanted a bigger skylight Edited April 4, 2021 by R1plusR2 Link to comment Share on other sites More sharing options...
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