Green Building Forum - Insulated raft verses Denby dale type foundations Sun, 25 Oct 2026 15:11:41 +0000 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Insulated raft verses Denby dale type foundations https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=225844#Comment_225844 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=225844#Comment_225844 Tue, 16 Jun 2015 21:31:55 +0100 joe90 Insulated raft verses Denby dale type foundations https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=225849#Comment_225849 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=225849#Comment_225849 Tue, 16 Jun 2015 23:07:48 +0100 ringi
I expect that if your subsoil will take a Viking hous type raft foundation without much MOT, it may be the cheapest option.]]> Insulated raft verses Denby dale type foundations https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=225851#Comment_225851 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=225851#Comment_225851 Wed, 17 Jun 2015 07:26:22 +0100 Triassic Insulated raft verses Denby dale type foundations https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=225883#Comment_225883 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=225883#Comment_225883 Wed, 17 Jun 2015 13:32:23 +0100 djh Posted By: TriassicI have a raft design and I told the SE I wanted insulation below. He called one of the manufacturers to discuss loading and has produced drawings showing the use of EPS 300 below the foundations.
Using EPS 300 everywhere sounds excessive, and AFAIK you can't get graphite in that rating. We have EPS 300 around our ringbeam and graphite EPS 70 elsewhere.

I don't know about relative costs.]]> Insulated raft verses Denby dale type foundations https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=225889#Comment_225889 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=225889#Comment_225889 Wed, 17 Jun 2015 17:39:35 +0100 woodgnome Insulated raft verses Denby dale type foundations https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=225891#Comment_225891 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=225891#Comment_225891 Wed, 17 Jun 2015 18:22:20 +0100 joe90
P.s. Woodgnome did you see my pm to you?]]> Insulated raft verses Denby dale type foundations https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=225895#Comment_225895 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=225895#Comment_225895 Wed, 17 Jun 2015 19:05:09 +0100 woodgnome Insulated raft verses Denby dale type foundations https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226010#Comment_226010 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226010#Comment_226010 Sat, 20 Jun 2015 08:50:04 +0100 Triassic Posted By: djh
Posted By: TriassicI have a raft design and I told the SE I wanted insulation below. He called one of the manufacturers to discuss loading and has produced drawings showing the use of EPS 300 below the foundations.

Using EPS 300 everywhere sounds excessive, and AFAIK you can't get graphite in that rating. We have EPS 300 around our ringbeam and graphite EPS 70 elsewhere.

I don't know about relative costs. it is excessive to use EPS 300 under the whole foundation, the SE took the easy option in specifying it. I will do the EPS loading calcs myself in order to reduce the amount of EPS300 being used and use EPS100 under the majority.

Not sure why you used graphite EPS?

Interesting question regarding the relative cost of EPS300 and 100, anyone got the costs?]]> Insulated raft verses Denby dale type foundations https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226026#Comment_226026 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226026#Comment_226026 Sat, 20 Jun 2015 17:53:59 +0100 djh Posted By: TriassicNot sure why you used graphite EPS?
Better lambda = U-value. We have 400 mm of graphite EPS to get the U-value we needed for PH. It's a downside of using straw for the walls; everything else needs to be super-plus good.

BTW, do check the availability of EPS300. When I did it I only found the place in Ireland that was supplying it. All UK alternatives only went to EPS250. But I may have missed something or things may have changed. My price was a package for all the EPS I used so I don't have a breakdown, sorry.]]> Insulated raft verses Denby dale type foundations https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226099#Comment_226099 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226099#Comment_226099 Mon, 22 Jun 2015 16:24:08 +0100 davidfreeborough
David]]> Insulated raft verses Denby dale type foundations https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226106#Comment_226106 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226106#Comment_226106 Mon, 22 Jun 2015 17:57:17 +0100 joe90
Having already spoken to the B.C.officer about foundations for the garage the ground is medium shrinkable clay and they have no problems with strip foundations at 850mm deep and a little wider than minimum so I guess they will not insist on S.E. Input for a trench foundation.]]> Insulated raft verses Denby dale type foundations https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226108#Comment_226108 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226108#Comment_226108 Mon, 22 Jun 2015 18:32:33 +0100 ringi
(I think lots of insulation under the slab is pointless unless you are having UFH, or insulation so well that you can save the cost of installing a heating system.)

I talked to one ICF vendor a long time ago, they claimed that with deap strip foundations, the cost of using ICF below ground was less then the saved concrete from a full width trench fill.]]> Insulated raft verses Denby dale type foundations https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226116#Comment_226116 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226116#Comment_226116 Tue, 23 Jun 2015 08:04:00 +0100 davidfreeborough
300mm of insulation below the centre of the slab probably doesn't bring much benefit, but 300mm below the edge of the slab is very worthwhile. An alternative approach is 150mm below the slab and an additional 150mm upstanding against the inner face of the inner leaf. However, combined with the insulation outside the inner leaf, this leads to very wide footings.

David]]> Insulated raft verses Denby dale type foundations https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226117#Comment_226117 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226117#Comment_226117 Tue, 23 Jun 2015 09:54:19 +0100 djh Posted By: davidfreeboroughUsing an independent trench fill foundation for the outer leaf could lead to differential movement between outer leaf and raft/inner leaf. I have seen studies from Denmark where an outer ring beam is used to support the outer leaf and this is joined to the main raft with steel rods.
That's quite similar to our situation where the bales need to be supported over their width. The original design had a separate strip foundation to support the outer edge, but we finished up with a ringbeam around the raft tied with some steel and concrete ribs. Still OK for PHPP bridging.

Posted By: joe90Having already spoken to the B.C.officer about foundations for the garage the ground is medium shrinkable clay and they have no problems with strip foundations at 850mm deep and a little wider than minimum so I guess they will not insist on S.E. Input for a trench foundation.

That sounds similar to our ground conditions, though we do have trees as well, and was another reason we ditched the strip foundation in favour of the ringbeam. I couldn't get a design that both the SE and the materials supplier would sign off on for clay heave protection under the slab whilst still maintaining the integrity of the sub-slab insulation. The insulation needs to be pressed against the slab, but that's not how heave protection works - it crushes.]]> Insulated raft verses Denby dale type foundations https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226127#Comment_226127 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13444&Focus=226127#Comment_226127 Tue, 23 Jun 2015 15:46:17 +0100 woodgnome Here is the sand screed to top of an EPS upstand followed by the 300mm EPS leaving a 150mm slab which we used the Cavity EPS as shuttering when we poured the slab.]]>