Concrete & Foundation Requirements for Steel Building Kits

Author’s Note: We have been in the steel building kit business for a lot of years and ship buildings to homeowners, government agencies, and commercial customers almost daily. We know the business. The article below covers a subject that we are frequently asked.

Through the years we have seen many sets of engineered plans for our steel buildings come through our offices. This has given us the opportunity to examine different concrete and foundation requirements for many different parts of the country. While we have attempted to provide you with accurate information with regard to what your concrete and foundation requirements will be, this information is not guaranteed to be what an engineer would specify for your unique circumstances but is intended to be used only as a guide in your concrete requirements.

You will find that steel building kits can be anchored on the ground (without a concrete floor) or on concrete. Before getting into particulars, if you are in an area that has a frost line, you will need to be approximately 12" under that frost line for your perimeter footings. This depth requirement for colder areas applies to ground anchoring as well.

The below described concrete applications do not account for frost line requirements.

Ground Mount (no concrete pad):

1.When mounting your steel building kit to the ground, you will be required to dig a post hole approximately 10” in diameter and 30” deep every five feet or every four feet depending upon whether you have purchased a 5’ on-center system or a 4’ on-center system.

2.Assemble your base rails and lay them in place, marking where your holes should be dug. (A 16 D nail poked into the ground through the pre-drilled hole in the base rails works very accurately for this.)

3.Next, use a post hole digger or auger and drill your holes 30” deep. Clean out the holes.

4.You would now lay out your steel building kit base rails according to the instructions and drop the ground anchors into the pre-drilled holes. Use a 2500psi concrete (pre-mixed bags or mix your own) and, using a shovel, fill the holes.

You should wait at least seven days for the concrete to properly set before moving on with the assembly of your steel building.

Concrete Mount:

1.Size the slab. You should make your slab 4” wider than the width of your steel building and 6” longer. This is so you don’t break or crack the edge of the slab when affixing the concrete anchor expansion bolts into your slab.

2.Concrete Floor: Your floor should be a minimum of 4” thick. Make it 6” thick if you are intending large vehicles such as trucks or larger RVs to be parked on it. The concrete should be a minimum of 2500 psi concrete with fiber mesh reinforcement added at the batch plant OR #3 rebar on 24” centers. You should also consider going with a concrete mixture of 4000psi along with the extra two inches of concrete if you are intending more than a normal amount of weight.

3.Be sure to saw cut expansion joints within an appropriate time after the pour is finished or trowel in the expansion joints while the finishing is occurring.

Footing Requirements:

(International Building Code 2000 or “IBC 2000” requirements)
At the same time you pour the floor, you are going to pour the perimeter footings. This is called a monolithic pour or monolithic slab. Perimeter footings need to be 12” deep (you can include the 4” of floor as part of the 12”) and 16” wide. The footings will have to have two #4 rebar lengths top and bottom, continuous run around the complete perimeter.

In our local area (Tempe, AZ), the footings would cost approximately $11.50 per lineal (running) foot.

That’s it. If your building department is still using UBC 1997 (Uniform Building Code), which many of them are, your footing only needs to be 12” wide. That should knock about $1.00 per lineal foot off the above footing price estimate.