Site Prep for Garages | How to Build a Garage Foundation | Horizon Structures

Site Prep for Garages

Site Prep for Garages

This information on how to build a garage foundation is intended as a GENERAL GUIDELINE ONLY.

We advise soliciting the expertise of a professional contractor who is familiar with local conditions and requirements to ensure you get the best foundation possible for your garage.

Site preparation for our prefab garages and double wide garages is usually more involved than basic sheds depending on your needs, your preferences or local requirements.

Remember, except for the board & batten style, all of our pre-fab garages - whether 1 or 2 car - come standard with a wooden floor. If you're concerned about deterioration from ground moisture, consider these upgrades:

Pressure Treated Floor Joists: Add $ .20 / square foot.
Pressure Treated Plywood: Add $.80 / square foot.
Pressure Treated Joists & Plywood Floor: Add $ 1.00 / square foot

*Any of our pre-fab garages can be built without a floor.

The other flooring option would be a concrete slab. It has been our experience that some local municipalities REQUIRE a concrete floor for any building used to house cars or trucks. Please make sure to check the requirements where you live before ordering one of our modular garages.

For a garage WITH a floor: A level pad of ¾" crushed stone, 3" – 4” deep, 1' larger than the size of the garage (for example, a 20’ x 24’ building would require a pad at least 21’ x 25’). This will allow for better drainage around the perimeter of the garage for rain/snow melt dripping off the eaves - especially, if you are not planning on installing rain gutters. Water splashing directly onto the ground will, eventually, create a muddy area and splash up onto the garage walls. The gravel base prevents this to extend the life of the building.
  • To prepare a gravel base, remove the sod from an area slightly larger than the pad, level the site by removing dirt where necessary, and spread the gravel to a depth of about three or four inches. Tamp the gravel down with a piece of 4-by-4 or metal tamper until it is evenly distributed and the site is flat and level.
  • A "frame" of pressure-treated 4x4's or cement block will help keep the stone in place and create a neater appearance; however, it is not required.
Curious about the cost to build a garage? For a garage WITHOUT a floor, still delivered in two modular pieces: A level concrete slab at least 4” thick and to the exact, outside, dimensions of your garage. You may want to consider a 6" thick slab for larger vehicles such as trucks or RVs.

For a garage WITHOUT a floor - BUILT ON SITE: Prepare a level concrete slab at least 4” thick and to the exact, outside, dimensions of your garage. You may want to consider a 6" thick slab for larger vehicles such as trucks or RVs. 

Frame out the perimeter with 2” x 4” or 2” x 6” pressure treated lumber, except for where the door will be, and anchor the wood into the concrete using J bolts. It is very important to prepare your concrete pad, including wood frame, to the exact size of the building because we extend the exterior siding down over the slab, and frame, to prevent water from coming back up into the garage. 

Keep in mind, if you choose to have a concrete slab as the garage floor, our carpenters will pre-build the garage in our shop, bring the pieces to your site and construct it on the slab. There will an extra charge for the labor to build on-site.

Although building modular garages on-site will cost extra for the labor, our customers have the advantage of being able to upgrade to a taller garage - 8’ side walls as opposed to 7’ side walls.

As always, please feel free to call us at  1-888-447-4337 if you have any questions regarding site prep for garages!

CLICK HERE to get a to-the-penny quote. It only takes about 3 minutes!

Garages | General Site Prep | 10 Garage Rules