Hi all, First post, bear with me.

I'm trying to build an affordable, low energy consuming home for my new family. Lots of really valuable info discovered, some great knowledge on here, thanks so far, i hope you can help with this one too?

We're building in a sandy area with low ground bearing pressure for the first 1m, then some soft clay, on top of Glacial Till which has great bearing capacity at 1.2m down.

We're in a high Radon area, needing full protection.

originally i wanted an insulated raft, for all its apparent performance, speed, simplicity with Radon barrier and supposed cost saving it seems to offer, but, gbp too soft for weight of house in this location to make it a realistic option without huge masses of concrete and rebar, suddenly not so simple, quick or cost effective. So, as a result it looks like we will be on strip foundations, with an insulated ground bearing slab, that seems a fairly reasonable solution to me?

The house is to have ICF walls. The structural engineer insists on rebar dowels out of footings and reinforcement carries on up the wall. windy area and fairly high side wall.

I understand in a masonry build the Radon barrier would just lap through the walls above ground. But how can effective protection be achieved with strip footings and rebar? I can't go over the rebar? Is the only way to go beneath the strip footings themselves?

That makes running the radon sump and sealing the pipework, along with any slab penetrations a whole lot of work.

I wondered if there was another simpler way?

Any advice much appreciated.

Cheers
Phil

How set are you on ICF? Would the SE insist on rebar if you had a timber frame? Never mind the radon, wouldn't you need a DPC anyway - how would that be done with rebar sticking up?

Posted By: phil303To bear our building on 50kn the engineers asked for a 1400mm wide x 250mm thick concrete strip with rebar in it, around the perimeter to support the raft and bulk of the weight

I don't understand why they want to bear the weight around the perimeter if its a raft? The whole point is to spread the load over the whole area. It's true that there is some load concentration at walls but that's reflected in the design of the raft. We have a 400 mm deep ringbeam (IIRC) but that's only 250 mm wide and was to do with the way the insulation is arranged, and there's a 100 mm (IIRC) deeper 'spine' where some roof loads are carried down.

The most i can infill is 600mm i thought?

There's no limit to the depth of infill that I'm aware of. I think if the depth is more than 1.2 m you need to do some special engineering calcs according to NHBC, but I'm no expert so please check with real engineers.

therefore now trying to work out how to run the Radon barrier under the whole footprint of the house

Presumably there are ways of sealing penetrations through radon barriers? It might be easier if the penetrations are bolts or threaded rod rather than rusty rebar? Another though might be to build the foundation and slab as one unit, then put the radon barrier followed by insulation and your floor on top. The only penetrations needed through the radon barrier would be a few bolts to stop the house sliding around I would have thought. And if you did something like that then a piled (or minipiled) foundation might work out best.

I think you are vastly over complicating something that doesn't need to be complicated! I build ICF on strip founds, not in a radon area but some of my detailing would work for you.

Firstly, I wouldn't bother trying to run anything under the founds. Too hard to do well. Just pour them as normal. Get your walls built up to DPC level, then do your first wall pour. Infill (the 600mm is NHBC guidelines not BR) - I infilled more than that in one corner. Just take your time, do it in layers with stable material and compact it well. Builders generally don't, and that causes NHBC claims which are expensive to sort which is why they get upset.

Put your radon sump in your top layer of hardcore as per manufacturer details. Fit your insulation and drainage pipes, ducts etc. Fit your radon DPM and lap this into your ICF. Not sure who your supplier is, but if you use Polarwall then you can get a really excellent fixing but lapping the DPM over the top of the inside insulation leaf and putting the plastic rail on top to hold it in place. Other systems YMMV but there will always be a way to do it.

You won't have a cavity to be collecting radon so can't see why the walls themselves would be much of a radon risk. You are already going to be collecting radon from the general area in the sump from under your house and venting it safely above ground.

Hope it goes well!

Posted By: Ed DaviesHow set are you on ICF? Would the SE insist on rebar if you had a timber frame? Never mind the radon, wouldn't you need a DPC anyway - how would that be done with rebar sticking up?

ICF won't necessarily need a conventional DPC - often an admix for the concrete to help make it waterproof, sometimes a paint on DPC like Sika Prufe can be used once the below ground pour is completed. Quite a few different details around.

I'm on Anglesey, North Wales. We're nudging closer to digging a big hole, hopefully get clearing the site and something going on next week.

Lewis is beautiful, i was up there windsurfing last summer, world class conditions on its day, i love that part of the world. Braga, Barvas, that neck of the woods.

We may need waterproof concrete for our build warranty, i'm investigating, although my engineer and alan said they only use it for basements, we'll see. You would think with 300mm of EPS in the floor and with xps encasing waterproof concrete in the walls from 1m below ground there's minimal need for a DPC anyway?

If you've got pix of the details and as things progressed i'd be really interested to see it as it took shape.