Alternative to concrete slab

[chirpychippy]

There is an access gap to my back garden that is equal to width of my hips and that is it, so getting a digger down to bottom of the garden is impossible as is getting a wheel barrow down there.

I am building a summer house/workshop so it needs good support.

I was looking at possibly using the concrete posts as per picture set into concrete, much like the principle for fence posts. Or making shuttering to form concrete piers set into the ground and then pushing the galvanised supports into the concrete.

Do you think either is feasible, I'm concerned about the shear capacity of the notched concrete post.

 

[Deluks]

If it's anything like a concrete fence post, it will be heavy and dense. If it's designed for a deck it should take a shed.

But for for the cost of it all, why not just knock up some concrete pads and sit the building on concrete blocks?

 

[chirpychippy]

If it's anything like a concrete fence post, it will be heavy and dense. If it's designed for a deck it should take a shed.

But for for the cost of it all, why not just knock up some concrete pads and sit the building on concrete blocks?

Thanks Deluks,

Concrete Pads?

Not sure what you mean Concrete Pads, are you saying like loads of small footings?

I was going make 12" x 12" Pads using shuttering ply. The mindset is the garden slopes, by using ply I can use my site level to get each pad the correct height, for a level base...

 

[Deluks]

Exactly that, with concrete blocks or stacked paving slabs on top.

But if you are building a ply box, why not just bring it to the height that you need? So that all the tops are level, and well clear of the ground.

 

[mrrusty]

https://easypads.co.uk/. What I used for mine.

 

[Ivor Windybottom]

If you build anything on topsoil then it will definitely sink. We had an old shed built on slabs, I'm sure it was perfect when first built, but it was like a fairground haunted house inside, tipping around all over the place. The middle of the floor was like a bouncy castle.

Those fence posts aren't going to be capable of taking much load. Easypads don't look any better than building on slabs - sorry but it's still going to sink eventually. Every time a worm tunnels under or a twig decomposes it will sink a tiny bit more.

If you really need a shed and definitely can't dig out then a concrete raft may be the least terrible solution.

Or something like the posts but more substantial, e.g. engineering brick pillars built on top of concrete.

 

[chirpychippy]

The approach I am taking is, I have dug 25 holes for 25 deck posts.
I have dug until I found clay average depth is about 800mm.
The posts will go in and the holes will be filled with a lean mix of concrete up to ground level.
The frame will be attached to the deck posts.
Build begins.

 

[mrrusty]

Easypads don't look any better than building on slabs - sorry but it's still going to sink eventually

I have dug until I found clay average depth is about 800mm

This is the answer. Our house stands on corbelled brick footings standing on the clay layer. My garden room stands on easy pads over compacted MOT sitting on the clay layer. Obviously if you build on topsoil it isn't stable, but for a garden room they are perfect and what they are designed for.

I wouldn't use fence supports. Easypads are designed specifically to spread the load over the footprint of the pad. The height is adjustable and the bracket plates are designed to take the timber sub-base.

Your home-brew solution may well work, or it may not. Personally I would rather use a solution which has been specifically designed and tested for the job in hand. If you email easypads they'll do you a layout design for the building you propose and specify which pads to use.

 

[Ivor Windybottom]

There's no way a building will remain static when built on topsoil, whatever claims the manufacturer of some miracle wonder-product says. It's built on top of decomposing biology, it definitely will not stay where it is.

Our wooden shed had buckled and bent all over the place. I'm sure whoever built it ensured it was all done as well as possible - it was on slabs on top of compacted sand on topsoil. But, a decade or two of worms and moles later, it was a creaking bent wreck.

 

[mrrusty]

@Ivor Windybottom - I think you are misreading this - the OP has a clay layer @ 800mm, and in my opinion if he builds off that he will be fine for a garden room. Perhaps one of the SE's on here will confirm. With my laymans hat on, when I did mine I looked online and saw firm clay has a bearing capacity of about 10kPa sqm which sounded OK to me.

 

[Notch7]

threaded bar set in concrete pads

 

[chirpychippy]

threaded bar set in concrete pads

I quite like this idea Notch7, it helps that someone is putting their name and reputation to it.

Cost wise its quite palatable.

Thank you.

 

[mrrusty]

Except oakwood garden rooms seems to be no longer trading... https://www.oakwoodgardenrooms.com/

 

[chirpychippy]

Except oakwood garden rooms seems to be no longer trading... https://www.oakwoodgardenrooms.com/

Well that instills no confidence, back to the drawing board...

Incidentally, in a bid to find out why they had ceased trading I came across a Reel from 1 day ago where said Summerhouse erecter is fitting kitchens.....hmmmm.

Mind you, and I know this, building your summerhouse is more expensive than buying one "on line" and most of his vids are pre covid, and we all know what happened to material costs post covid...hmmmm...

 

[Ivor Windybottom]

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.