Casting slab with 5cm S80 foam insulation at the bottom?

[biasb]

Hello.
The company I've hired for the extension has framed the mold for the footing of the crawl space "around" 120x60x5 cm EPS (S80). Reinforcement is also to be added, but will this handle the pressure, or is there a risk of settling?

I checked the compressive strength of S80, and it should be just 80 kPa, which corresponds to about 8 tons per sqm, so it feels relatively high, but the board doesn't have a large area.

I thought it's best to throw up a question here and see what opinions you all have.

 

[biasb]

After reading up a bit more, 80 kPa is the short-term load. What is meant by short-term? Is it an entire winter or a day?

I did a quick rough calculation on the load on one of the short walls where the trusses are placed:
The roof (half) is about 26 sqm.
Roof about 45 kg / sqm (rafters, tar paper, some extra, etc.)
That gives a total roof weight of 1170 kg (half).

Adding snow load (2.5 kN) gives 6630 kg.

Total with snow 7800 kg, and one short side has just over 2.4 sqm of cellular plastic, which gives 3250 kg / sqm, and this is just over the long-term load of 30 kPa. Without snow, it’s just over 475 kg / sqm.

Am I calculating completely wrong here?

Then there’s also the weight of walls, windows, interior, etc.

 

[Rabbithole]

You are probably counting correctly. S80 is weak there, I would have chosen S300. How does the insulation look otherwise, why is there 5cm under the wall?

 

[witten]

I haven't checked your numbers, but you should also add safety factors. Additionally, there is self-weight and live load from the floor slab of about 2.5 kN/m².

By long-term load, we mean the load combination for long-term in Eurocode, which is a formula with self-weight x 1 plus snow and live load significantly reduced.

A failure in cellplast is defined so that the settlement exceeds a given value. Beyond this, you may get cracks and settlements in the house.

 

[witten]

What kind of contract form is it? Are there no construction drawings?

 

[justusandersson]

You are thinking correctly. For a base plate that will be subjected to quite high pressure, regular foam board is not suitable. You need to set requirements for it.

 

[biasb]

What type of contract is it? Are there no construction drawings?

It's a "simple" extension with a crawl space that doesn't require a building permit, so we don't have any construction drawings.

 

[justusandersson]

Your "entrepreneur" clearly does not have the desired competence. If you can't skip him, you need to secure it in some way. The question is, has he ever done anything similar?

 

[Lostmoose]

Is it really relevant to have cellplast under a sole in that way at all?

 

[justusandersson]

It is always difficult to assess when you don't know the whole picture, but it looks a bit tricky. The idea of pouring a slab on top of what seems to be uncompacted macadam, for example. And what is the plastic underneath doing?

 

[Needas]

I think the execution of the form looks strange!
Weak timber, little or no support on the sides and of course the plastic and the foam plastic.
My thought is that the contractor has no clue.

 

[biasb]

It's always difficult to judge when you don't know the whole picture, but it looks a bit tricky. The idea of pouring a slab on what seems to be uncompressed gravel, for example. And what's the plastic doing underneath?

It's 10cm of gravel that they have packed with a compactor. I don't know why the plastic is there, I thought it was to prevent moisture from being absorbed from the ground and that the plastic should continue into the crawl space.

 

[Heij83]

Edge beams and formwork on our construction have at least S200

 

[C.Lundin]

I absolutely think it looks unpadded(word?). Also, as already noted, it is the completely wrong foam plastic. I also think the planned casting feels thin and that the execution, forming, for example, looks amateurish. I don't think this company usually works with this kind of thing, and if they do, I'm worried.

 

[Turbo_Tail]

Feels expensive and especially time-consuming with wooden molds. Don't you have something equivalent to the so-called "LammiTassu" molds in Sweden?