Garage conversion stud wall

20 May 2017
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United Kingdom
I am converting my garage into a habitable room. I need to build an internal stud wall to separate off the en-suite. I have a concrete slab floor which I am covering with a DPM then 50mm of celotex with 18mm chipboard T and G flooring with glued joints, floating on top. My question is: can I attach the sole plate directly to the chipboard flooring? Thanks in advance for your advice.
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Yes, but place a joist below where the plate will be
Thanks for the reply, just to clarify, I am not putting joists in, the t and g just floats on the insulation, can I just put one 50mm joist that sits on the dpm and then is fixed to the floor from above and then fix the sole plate through the floor into the joist?
Yeah do that.

Has 50mm of insulation been approved by the inspector? That's not normally enough.
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Yes, it has, as any more would take the finished floor level above the existing floor level in the house.
interesting, wonder if he would have been happy if there wasn't any room for insulation.
He's a nice inspector.
HI is though reading on various council websites about the requirements for floor insulation it seems that they make allowances for the fact it may not be possible to meet u values due to levels.
This is from one (Charnwood) admittedly from 2010:

Floor level with the house; if the floor is level with the house any insulation will create a step, so unless you are happy to step the floor this would be considered reasonable not to insulate but a DPM will be required if not already present, this can be a liquid paint bitumen type, generally 3 coats a...

He has been very helpful. He has let me do a non standard insulation of the roof too as it was not possible to get cross ventilation the standard way. I find they are very variable. I removed a chinmey internally and got a sign off retrospectively (it was all done properly btw) by an inspector who stuck his head through the loft hatch, I had to lend him a torch, and viewed it from 15 feet away and just said, "That looks solid enough". I have converted two almost identical Victorian houses to flats in the same city. One inspector made me insulate the external walls, one didn't.

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