Polystyrene Sub base

[scott225]

Afternoon all.
I'm currently building a patio in the back garden, its going about 3m from the house and across the back of the house.
The house is on a slope so the back door is about 1m from the ground at minute, they means the patio will require an awful lot of sub base, approx 20 ton if I've done the calculations correct.
I've already split the patio into 2 heights to try and reduce the amount of sub base needed, and planning to have 1 or 2 steps to the back door.

However, years ago my local council filled in a subway with polystyrene and put a road and paths over the top of it.
So can a type of Extruded polystyrene be used to fill in instead of sub base?

Many thanks.

 

[SpecialK]

Could you block and beam it?

 

[big-all]

you will need planning permission for anything greater than 300mm above ground level so would be restricted to 700mm below the back door with planning for any higher would seem unlikely

 

[freddiemercurystwin]

Planning issues aside (and that absolutely should be investigated before any building takes place), in theory you can use polystyrene as a fill, it's often used for heavy engineering works, under roads, railways etc, I've used it beneath concrete slabs no problems, you would be wise to speak to them to determine the necessary compressive strength and whether a concrete slab was required or not on top, beneath your slabs https://cordek.com/products/filcor-...tyrene) is commonly,part of a formwork system. As to whether it's a practical/economic solution would need some scrutiny.

 

[big-all]

would also suspect a full retaining wall to keep the foam fully captive so only compressive forces and no danger off sideways displacement and animal damage

 

[freddiemercurystwin]

No I don't see why a retaining wall would be necessary, earth behaves quite differently to polystyrene, it's made up of unstable organic matter and water which will want to slide and move about under gravity whereas polystyrene is completely stable.

 

[big-all]

i simply dont know just pointing out what i think may be involved
its more a "may not be as cheap and simple as you think " but off course further research wont hurt and will help clarify ??
as an aside they used about 2m under the tracks at part off the london bridge station rebuild
random link

 

[Notch7]

I remember a multi-storey car park got flooded on the ground level, the sub base had been packed up with a few hundred mms of Xps, the water got underneath and the whole floor floated up, crushing the cars parked up against the roof.

 

[freddiemercurystwin]

It's not some innovative newfangled use of polystyrene it's a tried and tested method of void filling and it could easily be made to work in this situation but as mentioned it may not be an economical solution here.