Opinions on foundation design

[Novisfixaren]

Okay, but how do you do it on the pages where a new insulated slab is cast against an old existing cold foundation?

 

[Oldboy]

I would think that some kind of insulation board, rodent-proofed on the edges, between the existing foundation and the new foundation/slab is suitable.

 

[Novisfixaren]

Hmm so cellplast isn't good enough?

 

[Oldboy]

It probably does. It counts as insulation, right? I've seen in other threads that there's been styrofoam in between, sometimes thicker, sometimes thinner. Styrofoam is the favorite material for foundations today. (It's just me who, in principle, believes that plastic doesn't belong in houses, except where no sensible substitutes exist, i.e. electrical materials.)

 

[corre]

I am probably more afraid that the slab will slide if it's not properly anchored.
With support on only two sides, on clay soil, with a heavy building, it feels like a risky construction.
You should ensure that the ground is properly grounded, not just on top of clay soil.

 

[Novisfixaren]

Thinking that the building isn't so heavy? Wooden frame, low ceiling, and metal roof.

Planning to excavation all soil and fill up with gravel, then 15cm of crushed stone on top.

Then I'm not sure how much it helps to anchor walls and roof frame to adjacent buildings?

 

[Oldboy]

Corre:
If the ground around doesn't slope significantly, then sliding shouldn't be an issue, right?

Remove topsoil and replace it with gravel and crushed stone, isn't that the standard preparation for a long time now?

 

[corre]

I'm thinking about the elevation of the ground level, and that it's only supported at two outer edges. Just pouring a 40m2 slab with a 100mm thickness will weigh around 10 tons.

Barns are usually constructed with simpler principles and with a "if it works, it works" attitude, so if a couple of columns have moved 10-15cm, it's not the end of the world, and it's always possible to dig out and replace the stone foundation afterward.
It's not quite the same principle with a slab on grade and a residential house on top, I mean.

But like many others, I'm an amateur in this context. I'd rather build a little extra than risk anything.

 

[Novisfixaren]

Will it work to let 30cm of these stick up above ground level or are there any such limitations?

 

[corre]

It is probably when casting that you might need to backfill a little extra. There are quite large movements when you vibrate the concrete.

 

[Novisfixaren]

I was thinking of using vibration-free concrete, but then the form pressure will be higher, won't it?

 

[Andreas_kalmar]

I think it will actually be less

 

[Novisfixaren]

How do you actually measure the easiest way when you are going to cast an extension against an old building?

Cross measurement doesn't really work then, does it?

Can you make a gigantic angle square like 3x3 meters in 45x95?

 

[Novisfixaren]

Can you cross-measure according to the picture first measure the black diagonal then measure the red diagonal to determine where the new outer corner should be?

 

[KnockOnWood]

Otherwise, you can take a look along the walls of the extension and the gable of the house, and aim for a point where they meet.
Feel free to use a string for assistance.

And don't assume that the old building and the extension are built perfectly at 90°!