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Replace suspended with insulation and screed on raft foundation base.


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Structural engineer came round today to assess if a few things were possible. While here we touched on the subject of our ground floor, which is generally sh!te with a touch of "it'll just about do" thrown in here and there. 

From work carried out last couple of weeks, it seems we have a raft foundation. The raft has dwarf walls on it, joists on those, total is about 270mm between top of what I assume is the concrete raft and the top of the current floorboards. I asked about ripping all the wood out and just filling with concrete, he's not happy about the weight loading if it is just a raft. He suggested we could consider putting a tonne of insulation in the void and just the minimum screed on top of that.

Didn't get to talk any further on it as time was up but I'm now wondering about this approach. Not something I have any experience whatsoever of so looking for any info, suggestions, methods, cost... 

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Many years ago when I was 19 I bought a house that needed everything doing Floors and joists where knackered and I did exact what you are proposing I ripped everything out then put a membrane in and up the side of the walls 50 mil of sand in then hardcore and 150 of runny concrete 

I still own the house and haven’t had any issues 

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4 minutes ago, nod said:

Many years ago when I was 19 I bought a house that needed everything doing Floors and joists where knackered and I did exact what you are proposing I ripped everything out then put a membrane in and up the side of the walls 50 mil of sand in then hardcore and 150 of runny concrete 

I still own the house and haven’t had any issues 

Wow 60 years ago. 

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13 hours ago, nod said:

Many years ago when I was 19 I bought a house that needed everything doing Floors and joists where knackered and I did exact what you are proposing I ripped everything out then put a membrane in and up the side of the walls 50 mil of sand in then hardcore and 150 of runny concrete 

I still own the house and haven’t had any issues 

S.E was definitely not happy about that idea. I'm just not sure on what his alternative proposal involves. DPM, chuck a tonne of PIR board in to fill up the void then minimum screed on top of that by the sound of it? From the reading I've done this morning that would need 65-75mm screed, I think. 

Would 75mm screed atop 175mm insulation atop a concrete raft be good? If I wanted to throw in UFH while we're making a mess, would I need to increase the screed?

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If you want to make up volume then 270mm isn't really that much. 

 

200mm of EPS  would do the trick nicely. 

 

From the top down. 

 

70mm screed with UFH Pipes stapled into EPS with long staples.

Slip membrane.

100mm EPS 70

DPM wrapped up the walls.

100mm EPS joints staggered to the top layer.

Sand levelling layer 

 

£11.33/m² is the cheapest I found after a 2 minute Google for 200mm and a U-value of about 0.18 W/m²K 

 

You could go even thicker, say 225mm to save the screed depending on the minimum required thickness of that. 

 

Screenshot_2024-04-18-12-15-33-762_com.android.chrome.thumb.jpg.b891e9a7ac98e0c6ef71be76bb2077fc.jpg

 

 

 

 

 

 

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Go to band p eps, they are a manufacturer not a re seller, save a fortune 

they will cut what thickness you want so you could go 

100mm eps

90eps

80mm traditional sand and cement screed. 
good thickness to keep the ufh pipes well covered and a good lump to use as a big radiator. 

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3 minutes ago, saveasteading said:

Looks like a typo for s and b eps in Dudley  ??

 

A great link thanks.

Not a typo, can’t remember the name of the company, so I thought a bit of google would find it, even with the wrong initials. 😉

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2 hours ago, Russell griffiths said:

save a fortune 

No prices  stated. They deliver direct to site. 

I'm predicting 20% saving cf merchants and presumably they want prepayment which could be quite  a big sum.

 

 

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3 hours ago, Russell griffiths said:

Go to band p eps, they are a manufacturer not a re seller, save a fortune 

they will cut what thickness you want so you could go 

100mm eps

90eps

80mm traditional sand and cement screed. 
good thickness to keep the ufh pipes well covered and a good lump to use as a big radiator. 


Just had a chat with them, very helpful people. Can't sell to me direct but gave me the name of a contact they sell to regularly that can help. Cheers for that!

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