missing screed perimeter insulation

[sm_jamieson]

It pains me to say this, but I may have made a minor c*ck-up. The sort of thing that for some reason just did not occur to you at the time ;-( When I layed the main concrete floor slab, I had insulation under and around the edge, as you do. The perimeter insulation was cut off level with the concrete slab. When I layed the screed (between 40mm and 70mm), I kind of "forgot" about perimeter insulation and screeded right up to the edge, sort of thinking about a good solid floor to the edges, and fogetting that

25mm insulation would be covered by plasterboard / skirting etc.

So I have a 5 inch concrete slab with underneath and perimeter insulation, covered with up to 3" screed touching the inner leaf below DPC (against the lapped DPM).

Now, obviously you cannot have perimeter insulation across the doorway, but there is around 15 metres of other wall.

Question: Is it worth cutting out a 25mm channel and adding permeter insulation, or is it not worth it now ? Floor will be tiled and no underfloor heating.

Simon.

[Tim Watts]

Without UFH I wouldn't bother. If you have insulation under the concrete I would think your edge losses though 3" with say a 15C surface temp will be next to bugger all, though that is more of an instinctive feeling rather than with real maths. Screed is not a thermal superconductor so the worse case is that the floor edge might run a little cooler than the middle - but I don't think it will be leeching

100's Watts out of your room.

Cheers

Tim

[sm_jamieson]

Thanks, its probably not a big deal. And wife would hate another dusty job ;-) Simon.

[andrew]

Question 2: Isn't one of the functions of the perimeter insulation to allow for the relative expansion of the underfloor concrete slab?

AJH

[sm_jamieson]

Yes, and is vital with underfloor heating, but there are loads of solid floors out there before they ever used perimeter insulation, so it must be OK for an unheated floor which undergoes far less temperature changes. I've actually got some air gap there anyway, since in some areas the vertical part of the DPM was slightly saggy and I didn't jam the screed up that hard against the side. Simon.