XPS300 Foam under finished concrete pier?

[jokkey]

Hello!

I'm going to start building the patio this weekend and I've been debating what to use as a base for the footings.
The current ground is topsoil, which then transitions to blue clay further down.

I've been recommended to lay the following at the bottom under each footing,

Cellular plastic XPS300 thickness 50mm, Compression strength (kPa) 300

Does that work? Should it be laid directly against the soil/blue clay and then the footing on top?
How do I level it easily so it's straight? Landscape fabric, gravel, and then xps?

Regards
jokkey

 

[andersmc]

Why should you use foam plastic? Is it to insulate against frost?

If that's the case, it shouldn't be under the plinth; it should be up at the surface.

 

[jokkey]

Hmm read this among other things...


Frost-Free Depth
How deep the pillar needs to be depends on the frost-free depth where you live. There are ready-made pillars that are 50 cm and 70 cm respectively. If you need deeper pillars, it is better to cast them yourself. You can "cheat a little" with the depth by digging a larger hole and creating a flat gravel bottom and placing a ground insulation slab of cell plastic before setting down the pillar. This makes it harder for the frost to creep under the pillar.

 

[bossespecial]

You write that you have clay and it is frost-heaving, so you should make proper pillars. The easiest way is to rent an earth drill and cast the pillar at frost-free depth. The other option requires a lot of digging. Then you don't need such strong XPS insulation since the clay is 10 times weaker. Regular EPS should suffice.

 

[prototypen]

A small amount of insulation under the plinth works poorly.
Place insulation over the entire deck area and slightly beyond at ground level (5-10 cm gravel/soil on top).

With a small amount, the cold just creeps around the edge.

Protte