One of the most difficult and important part of your garage is the slab.
Of course you site will dictate what you will have to do with your slab, in this article we will address several different scenarios - slabs on level ground, slab on grades falling from front to back and slab falling from back to front.
But first I would like to discuss footings.
Footing are required by codes everywhere and are essential to the long term stability of your garage.
Footings are the foundation of concrete which supports all perimeter load bearing walls.
Footings are required to be below grade a minimum of the freeze lines for your area.
In my state the freeze line is considered 8" below grade,this varies,depending on the area of the county you live in, In Kentucky its,24" and as you go north the requirements continue to go deeper.
In areas with sandy soil such as Florida the width and depth is also required to be greater.
Rebar is also required in most areas, usually at least 2 strands of ½" around the perimeters.
Rebar should be set 4" above the bottom of footings, using chairs.
Codes requires the any spliced rebar overlap a minimum of 2 ft.
We suggest that you contact your local codes department exact specifications.
In all cases a minimum of 4" thick slab should be poured, we recommend a minimum of 3500 psi concrete with fiber additive.
Slab on level sites: Monolific turn down slabs as they are called, are slabs which are formed and poured with the footings and floor all at the same time.
These slabs require a site that is fairly level (my cut off is within 24" of level.
) Turn down slabs should be formed at least 8" above grade, so that framings is adequately above the moisture of the ground.
These slabs should have a minimum of a 4" gravel base with a 6mil.
Poly moisture barrier spread over top of the gravel.
Make sure adequate bracing is installed around the perimeter of forms to prevent bowing when concrete is poured.
Slabs on sites falling from front to back: Any site that is more than 24" out of level usually will require a block foundation.
With this type of application footings will be dug and poured first.
Blocks will be laid and the concrete pour inside of the block.
If block height exceeds 4ft.
tall block should be reinforced with rebar tied from the footings up through the block and core fill with concrete.
If block height exceeds 5ft.
then you should consider going with 12 in.
wide blocks and reinforcing with rebar and core filling.
If 12in.
blocks are required, adjust footings to allow for 4in.
of concrete to each side of block.
Codes requires a minimum of 4" concrete to each side of blocks, using 8in.
block footing must be 16in.
wide, using 12" block footings should be 20in wide.
After block is installed gravel fill should be used to bring up to desired level and 6 mil moisture barrier laid over gravel.
With block foundations slabs can be poured with a couple of inches of fall towards the front.
Slabs on sites falling from back to front: This particular situation will require excavation.
Dirt will need to be removed to approximate driveway level.
Blocks will be laid similar to above and will be below grade.
All blocks below grade must be water sealed from the outside, to insure water will not leak through blocks.
We generally recommend installing a French drain to the outside of blocks below grade.
A French drain consists of a 4" perforated drainage pipe surrounded with gravel,which will ensure that water will be drained and eliminate water standing near blocks.
Rules for sizing blocks, footings and reinforcing will apply as above.
It is difficult to discuss every situation, but the above guidelines should encompass the majority of situations you may encounter.
Installing a slab correctly is difficult and should only be done by professionals.
As always be sure your contractor is licensed, bonded and insured and ask for references.
This article should give you a idea of what to look for.
Of course you site will dictate what you will have to do with your slab, in this article we will address several different scenarios - slabs on level ground, slab on grades falling from front to back and slab falling from back to front.
But first I would like to discuss footings.
Footing are required by codes everywhere and are essential to the long term stability of your garage.
Footings are the foundation of concrete which supports all perimeter load bearing walls.
Footings are required to be below grade a minimum of the freeze lines for your area.
In my state the freeze line is considered 8" below grade,this varies,depending on the area of the county you live in, In Kentucky its,24" and as you go north the requirements continue to go deeper.
In areas with sandy soil such as Florida the width and depth is also required to be greater.
Rebar is also required in most areas, usually at least 2 strands of ½" around the perimeters.
Rebar should be set 4" above the bottom of footings, using chairs.
Codes requires the any spliced rebar overlap a minimum of 2 ft.
We suggest that you contact your local codes department exact specifications.
In all cases a minimum of 4" thick slab should be poured, we recommend a minimum of 3500 psi concrete with fiber additive.
Slab on level sites: Monolific turn down slabs as they are called, are slabs which are formed and poured with the footings and floor all at the same time.
These slabs require a site that is fairly level (my cut off is within 24" of level.
) Turn down slabs should be formed at least 8" above grade, so that framings is adequately above the moisture of the ground.
These slabs should have a minimum of a 4" gravel base with a 6mil.
Poly moisture barrier spread over top of the gravel.
Make sure adequate bracing is installed around the perimeter of forms to prevent bowing when concrete is poured.
Slabs on sites falling from front to back: Any site that is more than 24" out of level usually will require a block foundation.
With this type of application footings will be dug and poured first.
Blocks will be laid and the concrete pour inside of the block.
If block height exceeds 4ft.
tall block should be reinforced with rebar tied from the footings up through the block and core fill with concrete.
If block height exceeds 5ft.
then you should consider going with 12 in.
wide blocks and reinforcing with rebar and core filling.
If 12in.
blocks are required, adjust footings to allow for 4in.
of concrete to each side of block.
Codes requires a minimum of 4" concrete to each side of blocks, using 8in.
block footing must be 16in.
wide, using 12" block footings should be 20in wide.
After block is installed gravel fill should be used to bring up to desired level and 6 mil moisture barrier laid over gravel.
With block foundations slabs can be poured with a couple of inches of fall towards the front.
Slabs on sites falling from back to front: This particular situation will require excavation.
Dirt will need to be removed to approximate driveway level.
Blocks will be laid similar to above and will be below grade.
All blocks below grade must be water sealed from the outside, to insure water will not leak through blocks.
We generally recommend installing a French drain to the outside of blocks below grade.
A French drain consists of a 4" perforated drainage pipe surrounded with gravel,which will ensure that water will be drained and eliminate water standing near blocks.
Rules for sizing blocks, footings and reinforcing will apply as above.
It is difficult to discuss every situation, but the above guidelines should encompass the majority of situations you may encounter.
Installing a slab correctly is difficult and should only be done by professionals.
As always be sure your contractor is licensed, bonded and insured and ask for references.
This article should give you a idea of what to look for.