There are various ways of constructing the garage slab in conjunction with the basement foundation. How the garage slab interacts with the mating wall – the concrete wall between the garage and the basement – is what we’ll discuss in this Technical Bulletin.
We’ll review the four most popular methods that are used in Metro Atlanta and North Georgia. We’ll also mention the pros and cons associated with each method, and tell you which method we endorse.
Method #1: On Top of Wall
Some homebuilders and contractors prefer to place the garage slab completely on top of the mating wall. Rebar loops are left out of the top of the wall and bent down into the garage slab prior to placing the concrete.
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Method #1: On Top of Wall
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Pros – If the mating wall was constructed in the wrong place (there can be discrepancies between the foundation plan and the Main Level plan), then it is easier for the framers to put the flooring system where it needs to be; Rebar loops provide a good connection between the mating wall and slab.
Cons – This method raises the entire flooring system 3 ½” to 4” above the top of the typical basement wall, which means the framers have to add 2x6s and half-inch boards to make up the difference on the rest of the tall basement wall. This is an additional expense.
Method #2: Slab Ledge
This method is popular with people that are concerned about water from vehicles travelling across the slab and into the basement. A 4” deep by 12” tall slab ledge is added to the mating wall. The slab is placed on the ledge.
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| Method #2: Slab Ledge |
Cons – This method lowers the garage slab, which requires an extra step up into the Main Floor. In many garages, that extra step encroaches into the vehicle space; The slab ledge is an added expense; There is not an easy, clean way to install rebar in the ledge to connect the slab to the mating wall.
Method #3: Slab/Sill Plate Combo
The top of the 10” concrete mating wall is shared between the garage slab and the floor system sill plate. This is our preferred method of constructing this area. It keeps costs down while minimizing the steps into the Main Floor.
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Method #3: Slab/Sill Plate Combo
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Cons – The position of the mating wall must be exact; The flatwork contractor has to remember to form the slab correctly.
Method #4: Barrier-Free
When accessibility is important – as it is in Active Adult communities and where wheelchairs and walkers are likely to be used – this is a good method to adopt. The top of the mating wall is raised while the floor system is supported by a stud wall inside the basement.
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| Method #4: Barrier Free |
Cons – The taller mating wall increases the price of the basement; The slab ledge is an added expense.
If you have questions about which of these methods is best for you, contact us at 770-795-0103. We’ll chat about your project and offer some suggestions.