Field_of_Dreams Posted January 23, 2023 Share Posted January 23, 2023 Hi All, I am just about to start laying the first course of my Isotex blocks on my insulated raft and have a dilemma about the best way forward in regards to the use of DPC. The slab already has the DPM installed underneath. I knocked up a quick drawing that shows the 2 options I have in my head...maybe both are not ideal but thats is why i'm here 🙂 Option 1 is what went to BC and they seem happy. Option 2 adds in the DPC and is how Isotex said to do it, but I have also seen Isotex installs, albeit abroad, where they dont use a DPC under the first course. Maybe there is a better way or maybe one of the options I have shown is not recommended? Keen to get some input from other who have been there before and have a far better understanding of the whole DPM/DPC thing! Any advice appreciated. DPC-Isotex Options.pdf Link to comment Share on other sites More sharing options...
Iceverge Posted January 23, 2023 Share Posted January 23, 2023 Option 1. DPC for DPC sake makes no sense to me. You already have a continuous barrier under all the house. 1 Link to comment Share on other sites More sharing options...
Chanmenie Posted January 23, 2023 Share Posted January 23, 2023 Why have you got a screed on top of the slab ? I’m building with Isotex but I have strip footings so I have just run the the DPC under the slab and over the footings, the first course of blocks will be laid on the DPC Have you asked Jamie or Dave at insulhub Link to comment Share on other sites More sharing options...
Field_of_Dreams Posted January 23, 2023 Author Share Posted January 23, 2023 2 hours ago, Iceverge said: Option 1. DPC for DPC sake makes no sense to me. You already have a continuous barrier under all the house. Thats what i thought but was told to use it. I did wonder if it could potentially create more problems (not sure what...just guessing) by using it...but it is cheap so wondered if the belt and braces approach would be wise. 41 minutes ago, Chanmenie said: Why have you got a screed on top of the slab ? I’m building with Isotex but I have strip footings so I have just run the the DPC under the slab and over the footings, the first course of blocks will be laid on the DPC Have you asked Jamie or Dave at insulhub Screed is for the UFH. Insulhub is who told me to use it but the more I research the more different opinions I get. Link to comment Share on other sites More sharing options...
Nickfromwales Posted January 23, 2023 Share Posted January 23, 2023 1 hour ago, Field_of_Dreams said: Screed is for the UFH It could have gone into the concrete, but not the end of the world. I've recently done one with the same spec, but persuaded all involved to ditch the screed and drop the pipes into the constructional slab. Works like a whopper of a storage heater if you heat the core, but will possibly be a bit more responsive if atop. Different horses / courses etc. I'm also bewildered at the constant detailing of this errant DPC, and see it with Velox, Nudura, and Isotex. My 2 cents is as above, EPS in non hygroscopic so pointless afaic. Link to comment Share on other sites More sharing options...
Chanmenie Posted January 24, 2023 Share Posted January 24, 2023 11 hours ago, Field_of_Dreams said: Thats what i thought but was told to use it. I did wonder if it could potentially create more problems (not sure what...just guessing) by using it...but it is cheap so wondered if the belt and braces approach would be wise. Screed is for the UFH. Insulhub is who told me to use it but the more I research the more different opinions I get. I’m surprised I though they usually suggested UFH in the slab, that’s what I have done. With the screed directly ontop of the slab you’ll be heating the slab anyway, so you could have saved the cost of the screed. Link to comment Share on other sites More sharing options...
Field_of_Dreams Posted January 24, 2023 Author Share Posted January 24, 2023 It is because the building was meant to be used for something that did not require UFH...its use has now changed to something that would benefit from UFH but this was only decided some time after the slab was poured. These things happen I guess 🙂 Link to comment Share on other sites More sharing options...
DrewG Posted January 24, 2023 Share Posted January 24, 2023 18 hours ago, Chanmenie said: Why have you got a screed on top of the slab ? I’m building with Isotex but I have strip footings so I have just run the the DPC under the slab and over the footings, the first course of blocks will be laid on the DPC Have you asked Jamie or Dave at insulhub I've short listed Isotex for my build and have below The strip foundations /slab /dpc detail as I see it (will most probably have the slab at 150mm). Doing it this way you ca clip the u/f heating pipes to the PIR Insulation (would add another DPC between PIR and under Screed. This would also be the detail for door threshold i.e. footing plus 2 blocks woth DPC. Link to comment Share on other sites More sharing options...
Chanmenie Posted January 24, 2023 Share Posted January 24, 2023 Again why have a screed and a slab, just put the UFH pipes on the PIR then 100mm slab. having a screed is like having 2 slants, you only need 1 Link to comment Share on other sites More sharing options...
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