Expanding a concrete foundation

[Boondox]

Okay, here's the problem. I have a 15x19' shop, a sizable portion of which is taken up by a stone fireplace with a woodstove insert so the place is useable in the winter months. So everything is on wheels, and some of the machinery must be physically removed and stored in the garage in order to do certain things...like using the bandsaw. The there is the table saw and the chop saw which live permanently in the garage because there's no room at the inn.

Besides which, the structure is full of rot and deserves to die and be reborn as a magnicent, roomy shop.

The concrete slab is in great shape. No cracks. Solid footings four feet deep. But along the back wall is a 3.5' high concrete kneewall, and along one end is a foot tall kneewall. How hard is it for a contractor to do that...and to extend the foundation so the shop can measure 20x30'?

Pete

 

[tc35dforme]

Pete, Maybe its just me, but I really don't understand your question. Are you looking to keep the two sides with knee walls and extend out on the other two ??

My experience with concrete...if there is a joint, there will be a crack. You can fill the joint with high tech elastomeric fillers and get by, but you will always see and feel the joint. This shouldn't be an issue in a shop.

As for extending the pour...get the contractor to drill the existing slab and drive in re-bar on 12" centers vertically in the frost wall and 18"-24" centers horizontally in the slab to tie the slabs together. If they undersize the drill holes the deformed rebar will fit well. They'll have to drive them in with a 5 pound hammer.

The key to sucess is COMPACTION. Do a good job in excavating and backfilling under the slab. Compact in short lifts 6-9" and be deliberate about it. You will never get another chance. If you have clay...be careful with water in the backfill. This causes the clay to expand and not compact well.

Hope this helps ?! /forums/images/graemlins/smirk.gif

 

[Anonymous Poster]

I can see getting rid of one wall, and making your new shed 19' x 30'. That would be re-orienting the building, which might not be practical for your site, but you would then have a building with one crack down the middle, 1/2 old, 1/2 new, and only need to shave down 1 knee wall, if the new part settles any (it will) it won't totally mess up all dimentions of your floor/ walls/ footers just the middle crack. That works for me. I can live with one moving floor crack.

Knocking out 2 footer walls, and pouring in an 'L' shaped new floor around the old floor and hoping the new footers don't settle different than the old footers..... ugh. Doesn't sound like good bang for the buck, but then I've never tried it either...

--->Paul

 

[Boondox]

I'm trying to keep the two sides without knee walls and push back the two sides with. On the high wall, I know I can push back three feet, but rocky ledge lies in that direction so I can't reorient the structure like Paul suggested unless I make it a split level.

No clay here. Pretty sandy soil on top of solid granite ledge. Thanks for the pointers on tying slabs together. Pete

 

[MarkV]

Pete, It sounds do able to me. You will be abandoning the existing footing under the knee walls and they would be replaced by new footing where the new shop walls would stand. It seems that a concrete saw could cut the slab inside the knee walls and the walls jack hammered to below grade. You got some good pointers on tying the old and new slab together or just put in an expansion joint and let the two sections be independent. The jackhammer could also be used on your rock ledge to gain you some room. Good solid granite ledge that is drilled and pinned with rebar makes a fine footing. Not easy work but do able.

MarkV