Alternative to concrete slab

[mrrusty]

If someone can point me at any information that suggests this method is satisfactory, then I'll believe it. In the absence of that, for any sort of foundation I would either follow the proven designs that are extensively documented, or use a product such as easypads that have been tested, and are obviously sold by the company with a liability for the performance of the product when installed according to the manufacturers instructions.

Anything else is a gamble - it might work, it might not. I thought long and hard about the sub-base for my latest garden room build, and concluded that using proprietary products with a substantial timber frame wasn't going to be a compromise. The timbers (200 x 100 main beams) and easypads for a 6.5 x 3.5 building with a deck extension cost the best part of £2K. Could I have got away with something cheaper? probably. But if you're going to put a £10K build on top of it, it seems a bit daft compromising for a few hundred quid. In my case a strip or raft foundation wasn't really an option because I didn't want the disruption and disposal requirements of using a digger.

 

[Notch7]

Looks like a good method to me, if a proper footing isn't possible. Although a chunk of metal sticking out of the ground definitely will rust eventually, galvanised or not. Rebar is normally completely encased in concrete, which preserves it, and even then steps are taken to stop the concrete getting too wet. It should outlive most of us though.

I think the threaded rod is stainless steel

 

[Ivor Windybottom]

I doubt that Easypad will take liability for anything. If it sinks they'll tell you to adjust it, whether it's accessible or not. If the Easypad itself breaks (it won't) they'll send you a new one.

They won't replace a broken floor or send a team round to rebuild the place after it's collapsed into the soft topsoil.

The holes down beyond topsoil aren't as strong as a strip foundation. But it's only a shed, not a 3-storey house. It will definitely be far more likely to stay put than anything floating on top of continuously moving and decomposing topsoil, which will absolutely definitely sink whatever anyone claims about their wonder-products.

They also function like piles, they grip into the surrounding soil all the way down. If a proper strip isn't an option then they're as good as you get. Still some soil to remove or redistribute, but a lot less than for strip foundations.

 

[Ivor Windybottom]

I think the threaded rod is stainless steel

It's galvanised, he says so in the video. Stainless would cost more than the shed.

 

[chirpychippy]

As you have guessed this really isn't my bag.

The garden drops in 5mtrs about 480mm,

I've dug, as I've said 400mm wide x 800 ish deep or to clay holes. There are 6 across the front six across the back, 3 down the sides and 4 in the middle. The base will be 5 x 2 c24.

To bring the levels up I now propose using concrete block on each concrete pier. Then bolting the frame to the blocks and or concrete piers.

I know footings are dug to clay for foundations, which is why I've dug to clay.

I can't see how it would sink using the same principle?

 

[mrrusty]

Sounds to me like it will be fine if it's concrete down to clay.

 

[chirpychippy]

Sounds to me like it will be fine if it's concrete down to clay.

I did my apprenticeship in carpentry working for a builder building extensions and loft conversions etc.

I know a bit about footings etc, but I am aware a bit of knowledge is a dangerous thing.

 

[Ivor Windybottom]

There are tables you can find with google that will tell you how much weight you can apply for each unit area. A 3 storey brick/block house needs a continuous strip that's 60cm wide. You'll need less, you need to find out how much less.

Work out the weight of the intended building, find out how much area of clay is needed to support it.

 

[chirpychippy]

There are tables you can find with google that will tell you how much weight you can apply for each unit area. A 3 storey brick/block house needs a continuous strip that's 60cm wide. You'll need less, you need to find out how much less.

Work out the weight of the intended building, find out how much area of clay is needed to support it.

If nothing it was an interesting exercise finding the accumulative weight of the entire structure. Base, walls, roof joists, osb boards, insulation, cladding, pool table, bar, 2 sofas, comes out 3100kg, let's say 3500kg or 3.5 Imperial tons.

And that's my lot, soil density is something I don't know the value of or understand.

I could find an SE to work it out, but I won't, I'm going concrete and rebar, if it sinks, I'll cross that bridge then...

Thanks.

 

[TimB100]

I'm going through the same thought process. 20+ years back I built my workshop on paving slabs. I placed them around 1.5mtrs apart and then used bricks to hold up wooden frame.
So that we can rule out that method I have to say that while the structure is still standing I had heavy machines inside and at those locations it sank. I also had to lever under the door up and stick blocks under it as it wracked a bit.

I'm now taking the whole thing down to build a summer house and small workshop. The new one is going to be built out of insulated roofing panels. Floor sides and roof.

Back to the footings.. I have decided to make pads and build in the lateral supports with rebar between the pads. It may be more work but I have learnt my lesson. Also needed for the roof panel. It's a terraced house with no side access so treated myself to an electric wheelbarrow. Estimated I need a 1 tonne bag of ballast and mixer.

I attach images of both

I hope another perspective helps

Cheers
Tim

 

[Deluks]

The easiest way to think of this is, if you go shallow, make it wide, if you go deep, it can be smaller.

Stack a few of these slabs atop each other and you will have the weight spread over a wide area, chances of it sinking are low, unless your ground is really crap, obviously you'd want to remove topsoil and dig them in a little bit.

Paving Slab BS 900mm x 600mm x 50mm D50 Grey

Widely used by the public in high volume pedestrian areas. The pimples on the surface create an added traction for maximum slip/skid performance.

lordsbm.co.uk

If you go deeper then get a digging bar and some post hole diggers, just make oversized fence post holes, a couple of feet down to well compacted soil, backfill with concrete, add rebar to taste.

 

[Deluks]

*duplicate post*

 

[chirpychippy]

The easiest way to think of this is, if you go shallow, make it wide, if you go deep, it can be smaller.

Stack a few of these slabs atop each other and you will have the weight spread over a wide area, chances of it sinking are low, unless your ground is really crap, obviously you'd want to remove topsoil and dig them in a little bit.

Paving Slab BS 900mm x 600mm x 50mm D50 Grey

Widely used by the public in high volume pedestrian areas. The pimples on the surface create an added traction for maximum slip/skid performance.

lordsbm.co.uk

If you go deeper then get a digging bar and some post hole diggers, just make oversized fence post holes, a couple of feet down to well compacted soil, backfill with concrete, add rebar to taste.

That's pretty much what I've done, dug bulbous holes to clay, back fill with concrete, add rebar. Then either use either a few of the 40 odd 600 x 600 x 50mm concrete slabs in my garden or go concrete block to raise the low end to level. Bolt it down on the off chance a tornado takes us to oz.

 

[Deluks]

That'll go nowhere. The fact that the building is raised means that any future adjustment will be relatively easy. Car jack and bits of slate!

 

[Ivor Windybottom]

The easiest way to think of this is, if you go shallow, make it wide, if you go deep, it can be smaller.

It's not as simple as that. The ground isn't a continuous mass of inert stuff. Topsoil is alive, things are constantly decomposing, tunnelling and dissolving in it. Clay or sand isn't much stronger, but the huge difference is it's basically stone particles and water. If you build something on clay or sand that it is able to support on day one then it will usually stay there. Whatever you build on top of topsoil will definitely sink, however much compacting or load-spreading you do.

The ultimate foundation is a raft, i.e. the entire area of the building. If you build a raft on topsoil then it will still sink, you just hope that it's strong enough to sink as a single entity and remain reasonably flat and level but even this doesn't always happen. I saw a porch on a house that had been built on topsoil, not a crack in it but it had tipped away from the house to a crazy angle as it was a 3-sided box so was much heavier on the outward side.

Many of the shiny flashy garden rooms that are currently being built on topsoil will be a mangled creaking wreck within a decade.