Is there such a thing as building an extension / garden room on 'stilts'?

[AsteriaBuffy]

Bear with me. We're looking at building a single storey extension / garden room but the side area of garden it would be on is very wet underfoot and in winter sometimes gets completely submerged.

Is there some kind of (maybe prefab) build that could effectively be built on stilts rather than a conventional concrete base? Would be even better if it was quicker and cheaper than a traditional build.

No builder is going to put footings for a building on sodden ground. Even "stilts" need to be set into concrete.

Why is the ground so wet?

There are plenty of properties built on stilts around areas that are liable to flood. very common, you just need the right people to plan it and do the work

You can put pretty much anything on piers or similar but as per a previous poster, whether that’s a good idea or not if the ground gets flooded is another story. Likely want to put significant drainage system in there first and then if that complex a structural engineer will tell you how deep any foundations need to be based on the soil type and amount of flooding. For an extension this step would be essential. For a stand alone garden room, well you may see it go floating off down the garden so probably a good precaution!

That's why I was wondering if it would be a better option to sink concrete 'stilts' down into the ground just at the corners, and have load bearing joists between them that the floor would sit on. The structure itself would be slightly above ground level and any water would flow / seep underneath it.

I thought that might be better than a big sunken block of concrete that water will then have to flow around.

It's wet there just because of the angle of the ground - there's a field behind the house that water seeps off when the ground is saturated (although it's pretty much on the same level). It's not all the time, just when the weather has been really wet for weeks.

Thanks all :)

What made me think of it was seeing ads for prefab stuff like Hup! but I think they do need conventional foundations?

Still in two minds about having an extension at all as hate the idea of all the disruption, and 'prefab on stilts' appealed as it might be quicker and easier. Might have been wishful thinking!

Sounds like a boat house. It would need planning permission. There must be architects and builders with experience along rivers like the Thames and Ouse where these are relatively common.

There is, but it’s not cheaper than a conventional build - it’s the opposite. Building on sodden ground is never going to be cheaper.

Your talk of concrete stilts made me think of this thread whereby she got a prefab extension that's built on giant screws in the ground. Op name changes a bit through the thread so don't select all on ops posts.

www.mumsnet.com/talk/property/4568138-modularprefab-extension

Thanks, that's really interesting, and beautifully documented by the OP. I'll have a proper read through.

I did this in my former marital home- a conservatory built on metal "piles" set in concrete and I wish I never had. Total waste of £11,000. It never felt right/stable, was a construction nightmare and the subsequent buyers pulled the whole thing down.