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Massive rocks for foundation  RSS feed

 
Tony Hedgewolf
Posts: 9
Location: Västerbotten, Sweden
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Hello All
So, amongst the list of things to do over the next two years is building the house in which my family will live.  The spot we've chosen for it is completely flat, very compacted and full of stones of various sizes and surrounded by more of the same (the area has been used in the past as  a business, fixing up heavy machinery so has had a lot of traffic on it).

The previoius owner of the land left us a large pile of granite rocks, each in the order of 1 to 2 tons and the idea is to build a single story wooden house on top of them.  Using the tractor and a sled made from two trees we've been able to position these lovely flat-topped rocks at key points of the perimeter of the house, where they've sat for a year without any sign of subsidence.

NOW.... the question is;  are we going to have to drill/dig holes in the spaces and sink concrete piers in order to 'lock down' the foundation, or should it be enough to move the rest of the rocks into those spaces and then crack on with the timber work?

I'd prefer to avoid concrete if possible and it just feels like these rocks are so big and represent so much combined weight, it's almost as if we'd be building straight on the bedrock! Not to mention how hard it will be to make holes or trenches in such packed ground...
 
Michelle Bisson
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Location: Quebec, Canada
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I cannot really answer your questions, but I have a few thoughts....

Are you building in an area where you do not need a building permit?  If you need a permit, then you would likely need an engineer to stamp your "non conventional" foundation.  Also, you will want to make sure that your foundation is below the frost line if you have one in the UK.
 
Travis Johnson
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I think in your location you would be okay. I have never been to the UK, but have been to Ireland and there (not so far away) there are legions of houses built on stone since your frost line (if any) is rather shallow. Here in Maine, stone foundations like that you describe were teh undoing of many houses built in the 1800's.

Frozen soil expands by 9%.

Period.

It does not matter if there is a dollhouse above it or a McMansion, it will move. It has to simply by the laws of nature. It is possible to build on stone, but it requires getting all the water out from under the rock, and this is prudent in any situation. Houses like dry feet (foundations) and a hat (well covered roof). You can find a lot of information on "rubble filled foundations", or "french drains", but if that water is drained off, and thus the soil has nothing to freeze, nothing moves. I would look into that anyway, but if you have lots of rock underneath, and severe compaction, then you might not have an option as digging sounds problematic.
 
Tony Hedgewolf
Posts: 9
Location: Västerbotten, Sweden
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Thanks for the responses!
Thanks also for the timely reminder that I needed to update the profile. I'm not in the UK any more, but in Sweden.
Yes, we definitely have a frost line here!

Since making that post we finally got hold of the guy who can sign off various crucial aspects of the build. He hasn't ruled out our use of the rocks, depending on a sample dig to see what is below the surface.

The method isn't all that strange in this part of the world, being seen under most old barns and a good number of houses (some of which are several hundred years old). It is still common practice to have a french drain around houses here too, so thar would certainly be something to consider.

I would like to hear more about the failures you mentioned though, always good to have all available information...
 
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