Concrete foundation for a mountain cabin

[Guldoxe]

Hello!
We are planning to build a mountain cabin in Vemdalen next year. The plan is to place the cabin on piers. I have some questions about this.

1. The ground consists of gravel and stone. Is it okay to backfill around the piers with this material, or must I fill with drainage gravel or something similar?

2. It's snow zone 3 where we will build. How deep should the piers be beneath the ground if I place them on 50mm insulation?

3. The cabin will be approximately 7x10 meters with a floor structure built with 45x220 joists. What diameter should the piers be?

 

[haavard]

1. If the posts are at frost-free depth, you can refill with existing masses.
2.http://www.traguiden.se/upload/anvisningar_och_produktion/bilder_konstruktiv_utformning/V-0312-G56-L.jpg
3. I would have taken 20 cm. Then there will be room for beams of double 45s.

 

[anaitis]

2. You should not PLACE it on insulation.
If you are going to use insulation, it should be around the plinth a bit below the ground surface.

 

[Guldoxe]

Thank you for the answers! When it comes to the insulation of the plinths, I have tried to find a description of how it should be done. What I found was this image and there it looks like you should place it directly on the insulation board. Is it wrong to do so? I am also interested in knowing how much shorter the plinth can be by insulating but have not managed to find that out.

 

[anaitis]

OK
With such shallow foundations, that is correct.
I was thinking of deep foundations.

 

[Guldoxe]

ok, so how do you think I should do ? According to the tables, the posts should be about 2 meters underground to be frost-free. Is it possible to insulate to reduce that depth or is it better to dig 2 meters and skip the insulation?

 

[mexitegel]

It is clearly stated in the document you yourself clipped from (http://www.isover.se/files/Isover_SE/Om_Isover/Kontakta_oss/Broschyrer_Bygg/Dow_Konsument_2006.pdf)

In table L2 on page 8, in your climate zone, you should have a foundation depth of 1 meter and 150 mm of insulation.

Without insulation, you have to dig down to the frost-free depth, around 2 meters.

 

[Guldoxe]

Absolutely right! I was reading poorly.

 

[hakaner]

If you are going to place the plinths on top of the insulation, you must:
1) Calculate the load on the plinths
2) Determine which insulation quality to use, e.g., XPS 250
3) Compare the calculated load with the insulation's allowable long-term load:
This will give you the area the plinths need to have against the insulation to
prevent them from sinking into the insulation.
-You will probably need to cast a footing on top of the insulation for the plinths to stand on

 

[Raskus]

How has it been going for you?
I'm considering building a cabin with the exact same measurements, also in the Jämtland mountains.
Have you gotten started, and if so, how did you handle the plinths?

I was also thinking of building on a plinth foundation, but possibly drilling them manually with the Skurupsborren or equivalent.