Insulated Raft Foundations and Build Lite

[LnP]

I'm shopping around for foundations for a timber frame structure with brick outer leaf. I don't plan to do it myself but will engage a ground works company to do the install.

 

I've not had a ground investigation yet, but indications are that I have good ground conditions, about 600 mm top soil with compacted gravel and sand below. I've had to dig holes and trenches down to about 1.2 m around the plot for various reasons, and never seen water.

 

I'm most interested in speed of installation, simplicity and cost. Regarding energy efficiency my expectation is that whatever foundations I go for, they can be made be good enough.

 

So I'm not wedded to any particular type of foundations and have been getting prices and talking to installers, suppliers and structural engineers to make my decision. I had been talking to AFT and an installer they had recommended, but as I mentioned in a previous post, AFT have ceased trading in the UK. The recommended installer is looking at carrying on his business with a different insulated form work supplier and is looking at Build Lite. 

 

I'd be interested in thoughts or comments on my approach but also on the Build Lite insulated raft system. I've attached their sketch from their website.

 

Thanks

 

[-rick-]

That's a pretty stonking great thermal bridge there. Not keen. Both AFT + Kore systems have thermally breaks between the inner and outer leaves.

 

With that thermal bridge I'm not sure why you would bother with the extra cost of an insulated raft vs traditional foundations.

 

What U value are they claiming?

[LnP]

13 minutes ago, -rick- said:

That's a pretty stonking great thermal bridge there. Not keen. Both AFT + Kore systems have thermally breaks between the inner and outer leaves.

 

@-rick- Thanks for your comment. Just checking, did you see the whole image? For some reason, after I uploaded it, I only see the whole image if I click on it and open it. Here it is uploaded a different way. Does that answer your question? They have a toe on the raft which the bricks sit on, but with a course of Marmox blocks. 

[-rick-]

I missed that before, sorry. Still not sure it really changes my view. Marmox blocks are good but they are still much lossier than the other mentioned solutions. There is also nothing stopping using marmox blocks with a traditional foundation and save all the custom eps/engineering costs (use it on the inner leaf and ensure the non-load bearing floor slab is thermally broken from the foundation).

Edited 3 hours ago by -rick-

[-rick-]

Expanding on my thoughts. If you have ground that suitable for this solution and are happy with the performance then it's a valid option if it is cheaper/quicker/easier to install. But I suspect you can get the same performance from a traditional foundation with somewhat lower cost (can get any groundworker to do it vs a specialist) and the industry is just much more comfortable with the engineering of traditional slabs which may make other things (insurance, future sale, warranty, etc) easier.