A man with a geotechnical survey machine

For better or worse, a soil study

With things progressing and our hopes elevated, we decided to go ahead with a soil study before signing. We’ve seen so many plots since this journey began, including:

  • plots that had already been terraced, badly, meaning drainage would cost a bomb.
  • inaccessible plots necessitating two or three pumps to get concrete to the site for a foundation.
  • sites so far removed from services we’d have to blow half our budget just to get water and electric to the site.
  • stunningly beautiful sites in summer, freezing cold in winter.
  • and so on…

This one, the one we want to build on, seemed to be ticking all the boxes. We were optimistic about the soil study and did it really as a formality and for peace of mind, hence waiting until the 11th hour. What we didn’t expect was a result to come back saying we’d need a footing that goes down to 1.8m.

Why? Well, no-one goes down to 1.8m here! The builders we’ve spoken to think it’s mad. The locals we’ve spoken to think it’s mad! Our neighbour (now sadly deceased) built his house himself on a 60cm foundation. Okay, maybe that’s not enough – it is clay after all – but to his credit the house, built with brick ~20 years ago, is still standing and I can say with certainty there aren’t any cracks in it because he never bothered to render it, so there’s nothing to hide.

But you can’t unknow the known. One the one hand we’re thinking, damn, why did we have this done? We could just have ploughed on with a (relatively) shallow foundation and worry about it later – but we wanted peace of mind with respect to the ground beneath. We were hoping for rock a relatively short distance below the clay. What we’ve got is not that at all.

In a future post I’ll write something about the etude de sol process. It was quick and looked pretty simple. The company we used, Sole Terre, work across France and we really helpful and sent out an engineer so we could get our report back before the August holiday, when all of France typically shuts down. He arrived with his van at 6.30am (it was a good job we’d decided to camp on site!) and just got on with it. Then, just 24 hours later, we had our report. Now the journey begins.

As far as next steps go we’re busy trying to get advice on a suitable foundation – suitable being both for the soil conditions and for our budget. This isn’t somewhere we wanted to be with this build – worrying about finishing before we’ve even started – but it is what it is!

This morning I’ve mailed a couple of UK-trained structural engineers who are based in France, so hopefully they’ll be able to offer some practical suggestions and put us at ease. We’ll see.

Questions for Stan

Foundations

  • Which is best? Slab on grade or vide santaire?
  • What’s the best way to insulate slab on grade?
  • How do we ensure the slab of concrete is level? 
  • If we decide to use form boards instead of breeze blocks, how do we make sure the blocks are level?

Foundation cement

Just asking for some very rough quotes for the cost of cement at 
http://www.toupie-beton.net/article/dosage-beton-14

Assuming we have a depth of 60cm (this is only guess work at the moment), we have an external wall footprint of 8m x 10m

Assuming the concrete base major support area is 1m deep (it will be less that this).

That gives us (for a 1 metre depth)

8 m cubed+ 8m cubed+ 9m cubed+ 9m cubed.

= 34 metres cubed of cement for 1 m depth.

So for 0.6 metres depth we need 20.4 m cubed. I filled out the form on the above site as below so am waiting quotes.