Jilly

Floor insulation for conversion

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Hi, I am just having the Building Regs drawings for my stable conversion and need your suggestions, please, as we have a bit of a dilemma because I want hippy, non off gassing stuff!

 

I need something relatively thin with a high compressive strength. Due to restricted head height, we ideally have only 70mm, but we might be able to use a little more. 
The p/a value is 0/566 (perimeter/area) 
 
The architect has quite reasonably suggested Celotex as a cost efficient solution. 
 

 

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What is the full floor make up ..?

 

Is that 70mm insulation with 100mm concrete / screed over ..?? Under floor heating ..??

 

Need to know that to comment. 

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Sorry, 150mm concrete slab with a painted on DPM or tanking. Th structural engineer has suggested a suspended floor. I don't want to underpin, and it seems screed and UFH will be too heavy. 

 

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So that’s 150mm on top of insulation ..??

 

Are there any walls built on top of it ..?? Structural walls not stud or non structural 

 

That is massively over spec for a ground bearing slab. 
 

Section drawing would be helpful. 

 

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1 hour ago, Jilly said:

The p/a value is 0/566 (perimeter/area)

 

Obvious typo, can you give actual exposed perimeter and floor area. What is your target U-value (building regs for England?).

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Sorry, the existing floor is a concrete slab, 150mm thick. The floor will go on top. The minimum u value we could have  is 0.28 (the 70mm Celotex would be  be 0.22, so that would be my target). 

 

The p/a value is correct. The building is just under 60m2. Ie 10+10+6+6/10 x 6 = 0.533 The 0.566 calc comes from the exact figures the architect has. 

 

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At 70mm the maximum thermal conductivity needed is about 0.024W/m.K so no realistic alternative. EPS300, thermal conductivity 0.033W/m.K would have to be at least 100mm to get 0.28W/m2.K The 150mm slab will spread any wall load to a considerable degree, wether sufficiently will depend on exact construction details 

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2 hours ago, Jilly said:

Sorry, the existing floor is a concrete slab, 150mm thick. The floor will go on top.


What floor do you mean going on top..??

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The insulation and floor will go over the old concrete stable floor. 

 

Edited by Jilly

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Take a look at insulating screeds. You could put down 70mm PIR then insulating screeds on top to give you your floor ready to finish.

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1 minute ago, Conor said:

Take a look at insulating screeds. You could put down 70mm PIR then insulating screeds on top to give you your floor ready to finish.

the first post said there should be no off gassing --thats limits choices 

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2 hours ago, Jilly said:

The insulation and floor will go over the old concrete stable floor. 

 


@Jilly what is the top floor surface ..? What are you putting over the insulation...??

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What is the distance from the top of the original floor to the top of the new floor surface and how flat is the original floor?

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Ok so @Jilly if you are saying you are putting a floating floor over the insulation which sits on the 150mm concrete then you have an issue. 
 

You’ll need to use min 90mm PIR and then float a 22mm chipboard floor that is then fitted with your final floor finish. That assumes that the current floor is dead flat, and if not you will need to use levelling compound on the slab to start with. 
 

You don’t need a liquid DPM - you can put that on top of the insulation and below the chipboard and use standard DPM with the excess taped up the walls. 

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Due to a restricted head height, we only have 100mm from the existing concrete floor to the top of the new floor. The concrete is levelish,  but its under a lot of rubber stable mats so I can't inspect it fully at the moment. (next job).

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@Jilly With 100mm build up, what does that leave your floor to ceiling height ..?

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Ok so I would seriously consider digging out the floor. It will be better in the long term and £2-3K spent now will pay dividends long term. 

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1 hour ago, PeterW said:

Ok so I would seriously consider digging out the floor. It will be better in the long term and £2-3K spent now will pay dividends long term. 

+1 to above, have you tried standing in a room with a 2.1m head height? with digging out you get to put in 200mm insulation plus screed and ufh and have more headroom

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We have explored this with the structural engineer and digging the floor out will compromise the foundations, meaning that we need to underpin: quotes for this have varied from £15-30K, so not an inconsiderable difference. We are compromising by taking part of the roof off to create a vaulted ceiling over the living room (I would rather spend money where I can see it!, with the lower ceilings over the kitchen part/bedroom and bathroom. Demolition is a non starter unless we do it 'accidentally' and I'm too risk averse for that. It's looking like Celotex it is! The other options are just too thick. 

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If you want ultra thin then look at Vacuum Insulated Panels or Aerogel. Both can do what you want at significantly thinner layers but at a much higher price. 
 

And is the SEng saying the floor is holding the walls up ..? Or that you can’t excavate down within a certain area ..? You could have the floor cut out say 300mm from the edge and drop the centre sections - again, not that cheap but not hugely expensive. 
 

£15-30k for underpinning a single storey building sounds a lot. How much wall is that..?

 

Have you had quotes from anyone such as Geobear who do the injected resin systems .?

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58 minutes ago, Jilly said:

(I would rather spend money where I can see it!,

and unfortunately, there is your problem.

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@Jilly tbh you should spend your money on the bits you cannot see, they are the important bits

i do believe you have a limited budget, but better to get a good structure and fill it with second hand furniture 

than a compromised structure that you cannot improve in the future when you realise it’s not come out as good as you wanted. 

 

Are you allowed to lift the wall plate up , thus lifting the roof. 

2.1 will be a major compromise, I would apply to lift the roof up by 300mm. 

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