Passive Raft Foundation

[MikeGrahamT21]

I've enlisted a Structural Engineer to confirm all the loadings and structural elements of the extension i'm going to be building, and one of the things he's suggested is going with Raft foundations, rather than strip foundations which I've used on the other 3 extensions i've built, hes quoted the fact its a coal mining area a raft would be more suitable, and i'm happy to look into it as in my mind there should be less digging and soil removal, and also less concrete used, which has to be a good thing for the planet.

 

So I've been looking into passive raft, though don't have much clue about it having not used it before. Construction is a brick/block cavity, single storey, 5.5x2.4m. The existing bungalow has timber suspended floors, am I right thinking if you have passive raft you have concrete floor in that portion, or can you still have suspended timber?

 

I've not found anywhere who sells the insulation jigsaw bits, so I'm hazarding a guess that this is a specialist design and ship job as a minimum. I've contacted a couple of suppliers who advertise passive raft, but I suspect it may be some time before they reply.

 

There is existing drains where the extension is to be built, which are going to be replaced by new pipes, would a passive raft be OK to be built over the top of these old drains to save digging them out?

 

Currently got block paving down where this extension is going to go, 100mm sharp sand, followed by 300mm MOT Type 1, removing the sand, is this suitable for a passive raft to sit on?

Regards

Mike

Edited April 20, 2020 by MikeGrahamT21

[zzPaulzz]

Hi Mike.  Did you find a solution to your passive raft requirement? I’m looking at the same situation now for my build.  

[Beau]

Might have a good idea for you? https://viking-house.co.uk/passive-slab-insulated-foundations.html

[zzPaulzz]

Thanks @Beau that’s useful site though it doesn’t have a suspended raft option.