Did you know that there are a number of different types of foundations that can support a detached garage. One of the most common foundations for a detached garage is a thickened edge slab. This foundation is also sometimes called a slab thickening foundation, a floating slab, or a slab on grade. Keep reading to find out if a thickened edge slab is the right garage foundation for you!
Required Site Conditions Thickened edge slabs are a good foundation option for a detached garage if the ground you will be building on is level and the ground below the garage is original undisturbed soil. If you have a sloping property, or if extra soil was added to your yard to bring up the grade level, you may want to contact a structural engineer to determine the best type of foundation for your new garage. Applying for Permits Check with the City that you are building in to find out if you will need engineering for your building permit. Most cities will only require engineering for a garage slab foundation if they consider it “oversized”. Each city, town, and county has their own definition of what is considered oversized. Fortunately, most places have the size limits listed on their websites or building permit applications, so it is easy to find out if you will need engineering. What is an Engineer’s Verification? If an engineer has designed a thickened edge slab for your new garage, an engineer’s verification might be a condition of your building permit. Depending on the City your building in, this is sometimes also called an engineer’s letter of compliance of certification. It is best to know ahead of time if this will be condition of the permit, so check with the city when you get the permit. Many cities, towns, and counties, require an engineer to review concrete slab foundation and produce a sealed letter confirming that the construction is consistent with the design. If you need a verification letter, the engineer will need to see the base preparation and steel rebar before the concrete is poured. The structural engineers you choose might be able to give you a verification letter based on photographs. If this is the case, make sure you send your engineer all the right pictures and get the engineers approval before the concrete is poured. Once the concrete is poured you won’t be able to make any corrections the engineer might point out. The picture will need to clearly show all the components of the design, including:
Compacted sub-base material
Vapour barrier and insulation
A picture of the entire slab reinforcement
Using a tape measure, show the depth the concrete will be at various locations including the thickened edges
Using a tape measure, show what the concrete cover will be above and below the rebar
Using a tape measure, show the spacing of the rebar
Close up pictures of the rebar in the thickened edges
Your engineer may also want the concrete ticket
Your engineer may also want receipts indicating the materials used during construction.