Bricks, Masonry, Asphalt and Concrete - Footing & Slab
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ollie
10-19-05, 08:35 AM
Hi
I read some where on the web about the relationship between a slab and the walls of a foundation. I can't find it know ... so ...
We will be building a addition in northern NY State (20'X40" two levels) I guess the footing will be below the frost line and a wall will be coming up to meet the slab. Should the slab be poured so it's inside to walls for the foundation or should it cover the walls of the foundation. Does it matter? If poured inside should there be an expansion joint around the outside of the slab. The space will be used for a workshop and will have minimal heat, above will be living space.
Ollie
I read some where on the web about the relationship between a slab and the walls of a foundation. I can't find it know ... so ...
We will be building a addition in northern NY State (20'X40" two levels) I guess the footing will be below the frost line and a wall will be coming up to meet the slab. Should the slab be poured so it's inside to walls for the foundation or should it cover the walls of the foundation. Does it matter? If poured inside should there be an expansion joint around the outside of the slab. The space will be used for a workshop and will have minimal heat, above will be living space.
Ollie
Concretemasonry
10-19-05, 10:41 AM
You did not mention if this was a basement shop or a ground level shop.
For a basement situation, the standard construction would be to pour a continuous reinforced footing for the wall. The wall is built on the footing. Later, the concrete floor is poured. The slab will be poured on top of the exposed interior part of the footing (usually 4" - 6"). The slab should poured on compacted soil with a vapor barrier. You do not need to put joint material between the wall and the slab, since the slab will shrink and put away as it cures. The joint can be taken care of later. I would definitely put in drain tile around the interior to insure a dry shop. The tile could also help to keep the existing stucture dry by lowering the water table slightly.
If it is a shop on grade, the slab inside would be floating and supported 100% by the soil under the slab and have no connection to the walls.
Since you are building an addition, drill into the existing footing and insert rebar to tie the old and new footings together to prevent differential settlement. Make the new footings the same width as the old if possible. Typical footings are 20 to 24" wide and 8" thick.
Good luck!!
Dick
For a basement situation, the standard construction would be to pour a continuous reinforced footing for the wall. The wall is built on the footing. Later, the concrete floor is poured. The slab will be poured on top of the exposed interior part of the footing (usually 4" - 6"). The slab should poured on compacted soil with a vapor barrier. You do not need to put joint material between the wall and the slab, since the slab will shrink and put away as it cures. The joint can be taken care of later. I would definitely put in drain tile around the interior to insure a dry shop. The tile could also help to keep the existing stucture dry by lowering the water table slightly.
If it is a shop on grade, the slab inside would be floating and supported 100% by the soil under the slab and have no connection to the walls.
Since you are building an addition, drill into the existing footing and insert rebar to tie the old and new footings together to prevent differential settlement. Make the new footings the same width as the old if possible. Typical footings are 20 to 24" wide and 8" thick.
Good luck!!
Dick
ollie
10-19-05, 11:55 AM
Dick
This is going to be a ground level slab. The present house is a three season cabin on a lake. The addition will be added to make it a four season home connected to the original house by a breeze-way. Connecting to the original house foundation is not an option, the cabin is built on piers.
Because the lower floor is never going to be living space my thinking is to have a free floating slab pured. With good prep work and drainage and strong enough construction the slab it should not crack. If it heaves there will be less chance of it affecting the rest of the addition. Does this sound right?
Ollie
This is going to be a ground level slab. The present house is a three season cabin on a lake. The addition will be added to make it a four season home connected to the original house by a breeze-way. Connecting to the original house foundation is not an option, the cabin is built on piers.
Because the lower floor is never going to be living space my thinking is to have a free floating slab pured. With good prep work and drainage and strong enough construction the slab it should not crack. If it heaves there will be less chance of it affecting the rest of the addition. Does this sound right?
Ollie
Concretemasonry
10-19-05, 03:45 PM
You have two choices -
1. Concrete footings below the frost line and 8" block at least 8" above the slab elevation. From there you can continue block up for the garage walls. The slab (4") with wire mesh would be a floating slab on compacted soil, between the block walls. The top of the 8" block wall (either at 8" up or 8' or so up) would have a treated sill for stick building above. This would not heave.
2. A floating slab (6"?) with reinforcing steel and thickened edges. This should have 1 course of block on top all around except at the door to keep the wood framing above the surrounding grade. A floating foundation like this can heave with the amount depending on the type of soil and the exposure on the different sides.
Despite your best intentions, a 20 x 40 concrete slab will crack since concrete shrinks as it cures. This is especially true with the temperature swings you will have. The trick is to plan for it and know where it will crack. A floating slab (#2) is more difficult to control the cracks because of the thickened reinforced edge.
Both slabs should have 10 mil poly and rock under them to minimize the moisture what can get into the addition.
Get some plans and a permit. New York has a history of dificult to deal with on some grandfathered structures. This also helps on selling and guaranteeing insurance coverage.
Good luck
Dick
1. Concrete footings below the frost line and 8" block at least 8" above the slab elevation. From there you can continue block up for the garage walls. The slab (4") with wire mesh would be a floating slab on compacted soil, between the block walls. The top of the 8" block wall (either at 8" up or 8' or so up) would have a treated sill for stick building above. This would not heave.
2. A floating slab (6"?) with reinforcing steel and thickened edges. This should have 1 course of block on top all around except at the door to keep the wood framing above the surrounding grade. A floating foundation like this can heave with the amount depending on the type of soil and the exposure on the different sides.
Despite your best intentions, a 20 x 40 concrete slab will crack since concrete shrinks as it cures. This is especially true with the temperature swings you will have. The trick is to plan for it and know where it will crack. A floating slab (#2) is more difficult to control the cracks because of the thickened reinforced edge.
Both slabs should have 10 mil poly and rock under them to minimize the moisture what can get into the addition.
Get some plans and a permit. New York has a history of dificult to deal with on some grandfathered structures. This also helps on selling and guaranteeing insurance coverage.
Good luck
Dick
ollie
10-19-05, 04:24 PM
Thanks Dick
We are in the early staged of design and will have an architect design the building and have a contractor do the shell. We will do the inside finishing. I was just wondering if there was an advantage to doing it one way or the other. I guess not.
Ollie
We are in the early staged of design and will have an architect design the building and have a contractor do the shell. We will do the inside finishing. I was just wondering if there was an advantage to doing it one way or the other. I guess not.
Ollie