A 1.8m deep foundation, really?

After receiving the results of the soil study, we had to dig deep in more ways than just into the ground. Was it all over before we’d begun? It took about three weeks to stop panicking. We started reaching out to contractors to try and get prices then we could make a decision. We weren’t signing for the land until mid-September (in the end we signed yesterday) so as that gave us a few weeks to find a quote we could afford – or not, in which case we would have to forgo our deposit and walk away.

After hearing nothing back from any of the contractors who we contacted, we called a builder who we knew from our first 6 months living here. He’d helped us out when we were first looking, had visited some potential plots with us, advised us on foundations there, and even put together a devis for an affordable wooden house! For some reason he wasn’t the first person we’d thought of – but he should have been.

A few meetings later and we had a plan. More importantly, an affordable one. The only hitch was that we’d need to redesign the house. Could we afford the foundation for a single-storey? If so, what size? This guy was so patient! He came out out to the site, bringing along the landscaping guy, and finally we had a quote: just under 30k for the foundation, the driveway construction, and the trench for connecting services. Just over half our budget – but that would be alot of heavy work done which would speed things up for us. Yes, we’d thought we’d DIY this too, but by the time we’ve factored in the time and expense of hiring diggers, laying rebar (after learning how to do it!) it seems the most sensible approach. We really just want to get on with it.

On the 19th September, after much to-ing and fro-ing we submitted a modification to the original building permit. We need to change the design from two storeys to one and make the footprint ever-so-slightly larger.

Here’s how it looks.

The Single-Storey Plan
And the view from the front (with terrace added) in situ.

It’s a big change, but we think that having had the soil study and being put in the situation has done us a favour, for several reasons.

  1. It’s going to be way easier (and faster) to build a single-storey house! The plan is now for the builder to do the foundations and then the roof, so we will build the walls and do all the internal work, but doing it this way saves us time and also costs us less in materials, as he gets discounts we don’t and is only charging for his time.
  2. We were concerned about the seismic safety of a two-storey GREB house and our attempts to find out anything official about it weren’t really coming to anything. We were looking at having to pay several thousand euros for Simpson Ties, to strap the two floors together, which would have been expensive. The only contractor we talked to about seismicity suggested a different method of construction. We have no such concerns about a single storey.
  3. We are less likely to run out of money. The risk with building two floors is that we find out after building the first that we can’t afford to build the second. With a single storey once it’s done, it’s done: roof on and away we go!
  4. Maybe we didn’t need all that space anyway? The thing about having two floors was some of the bedrooms were going to be huge. That’s a lot of space for sleeping in. We justified it on the basis that small children grow up into teenagers, which they do – but at some point after that they also grow up and (eventually) leave home, leaving us with a huge empty house. The single-storey design is as space efficient as can be and, if we need more space, we have half a hectare of land to fill! Plenty of room for small cabins (below the 5m2 threshold for tax, of course :-)) and other outside spaces we can use together. What teenager wouldn’t prefer a “kids cabin” just for them (think sofa and mini fridge) than a humongous bedroom with their parents next door?

There’s still a lot to do but we now have our new plans in and our names on the deeds, so we can start to move forward.

Next steps then:

  • Connect services (water, waste and electricity)
  • Build a driveway so we have access.

Oh, and having decided to go single-storey we went back to the soil study people and asked about the foundation depth. Now all we need is 90cm. Phew! That chops about 5k of the price. Brilliant!

Watch this space!

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.