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KingCrabLegs 06-17-2013 10:47 AM

Foundation help
1 Attachment(s)
I'm adding a 12'x5' bathroom to an existing 40x40 outbuilding and I need some advice on what type of foundation to use. The outbuilding is built on a concrete slab and I was planning on doing a concrete slab for the new bathroom as well. However the grading drops away a bit and it seems like it might be too much for a slab. You can see in the picture below where I have *temporarily* framed up where I was going to do a slab. Those are 2x10's around the outside and the top is level with the slab of the existing outbuilding. You can see in the back left corner where the 2x10 doesn't even extend down to the current grade.

Any thoughts on the best way to do a foundation for this? (Ignore the big hole in the picture, I had to remove a huge stump. Also the 2x4 cross beams are only there while I was checking the spacing)

Attachment 72794

Willie T 06-17-2013 11:04 AM

Stake that form you already have, backfill it, compact it, and go for it.

MTN REMODEL LLC 06-17-2013 11:41 AM

Where are you located... I know it's an outbuiding.... but are you sure you are on a floating slab and you don't need some footers/stem?

You are probably fully aware... just checking:)

KingCrabLegs 06-17-2013 11:47 AM

I'm in western Washington state. I'm fairly sure it's a floating slab.

On a related question - should I tie-in the new slab with the existing in way? (how?). Or should I just put a piece of wood between the two or just put the new slab right up against the old?

MTN REMODEL LLC 06-17-2013 12:03 PM

If you are in Washington.... do you get freezing up there.

If you are on a floating slab, adding on, you are at risk of differential settlement and/or heaving.... depending on soil and weather functions.

You can certainly minimize the issue by tying the slabs together well, compacting your base well, and controlling any water from your foundations. (Shy of some fancy expensive post tensioning technique, I don't know of a perfect solution to two semi independent pads... maybe some one will instruct us and have a better idea).

If your existing SOG has a foundation (footer/stem or mono-pour), you will want to do the same with your bath slab... and still tye them together.

Are you familar with how to tye them together.

KingCrabLegs 06-17-2013 12:29 PM

It gets below freezing for a max week or two every year. Temps are usually 40-50 in the winter.

Nope, not familiar with how to tye them together.... yet. I'd imagine it involves a fair bit of drilling into the existing slab for starters...

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