Preferred insulation options from your point of view?

Almostuseful · 24 Sep 2017

morning all, finalising some details for my extension today, and wonder from a builders point of view what the preferred options for floor and wall construction are.

We have a concrete slab, which I’m proposing to be 150mm concrete slab over 150mm insultation, screed on top.

And the walls I’ve currently got as masonry outer skin, 150mm cavity with 100mm insulation fixed to inner skin, plaster finish inside.

Both are fine from a building regs point of view (copied from standard details on other projects) but from the builders point of view would you prefer slab - insulation - screws and for the walls 100mm full fill insulation as alternatives?

I’m not fussed either way (although 100mm internal extra space appeals!) as we have concrete floors with no insulation in the rest of the house, and 50mm cavities elsewhere so anything is an improvement!

Cheers all.

tomfe · 24 Sep 2017

Floors either 100mm concrete, insulation, then screed. Or if you can get a good finish insulation then concrete. I power screed all my floors so they are flat and poor carefully so they are the correct level.

You've got a 150mm cavity which I think is the way forward as you can use the cheaper full fill and get good uvalues.
Wet plater finish internal will help with airtightness.
Though I have seen solid wall and ewi when finish is render being used more.

However as you say the rest of the house is poorly insulated so depending on layout you may find little benefit in having more insulation in your extension. But then again it may not cost you much extra to heat that extra space.

Almostuseful · 24 Sep 2017

Thanks. Out of interest I see that the concrete should be allowed to dry out at 1 day per mm before the insulation is put down, given it’s a 6 week build programme I wonder how that works in practise? I figured the insulation/slab/screws might have more leeway to lay the screws on to the concrete. Is it not really an issue?

^woody^ · 24 Sep 2017

Sod the builders. Do what you want.

Almostuseful · 24 Sep 2017

Nah, it’s nice to be nice isn’t it. I couldn’t care less what they put in to be honest as long as it complies with BR, might as well make things easier for them.

tomfe · 24 Sep 2017

Almostuseful said:
dry out at 1 day per mm

That's screed, not an issue for concrete as you'll have a dpm over it anyway.

Almostuseful said:
lay the screws on to the concrete

What screws are you on about? Are you putting police under the floor?!?!

^woody^ · 24 Sep 2017

Almostuseful said:
Nah, it’s nice to be nice isn’t it. I couldn’t care less what they put in to be honest as long as it complies with BR, might as well make things easier for them.

Arrrr. I'm coming down there to build it

Almostuseful · 24 Sep 2017

tomfe said:
[QUOTE="Almostuseful, post: 3993442, member: 228455" dry out at 1 day per mm

That's screed, not an issue for concrete as you'll have a dpm over it anyway.

What screws are you on about? Are you putting police under the floor?!?![/QUOTE]

Sorry, fat fingers, meant screed!

Almostuseful · 24 Sep 2017

^woody^ said:
Arrrr. I'm coming down there to build it

See you at 9am?

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Preferred insulation options from your point of view?

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