Concrete and foundation requirements for steel building kits
Steel building kits are becoming a very popular choice when it comes to the construction of new buildings. You can usually build a steel construction kit much faster and much cheaper than a traditional wood frame building. They require virtually no maintenance, and for smaller buildings, you don’t always need a contractor to build them.
A detail that will have to be resolved before building, and before buying, is what will the building stand on? Naked dirt? Concrete? Concrete foundations add to the overall cost of the project, but may be required for a larger building or structure that will be permanent. The main type of steel structures that are on earth foundations are carports. But depending on local requirements, steel buildings can sometimes be built on bare ground. The following information will illustrate some details about earth foundation and concrete foundation.
You will find that steel building kits can be anchored into the ground (no concrete floor) or into concrete. Before I get into the details, if you are in an area that has a frost line, you will need to be approximately 12″ below that frost line for your perimeter foundation. This depth requirement for cooler areas also applies to anchoring when I usually.
The specific applications described below do not take into account the requirements of the frost line.
Ground mount (no concrete pad):
- When mounting your steel construction kit in the ground, you will need to dig a post hole approximately 10″ in diameter and 30″ deep every five feet or every four feet, depending on whether you have purchased a 5″ center-to-center system. ‘ or a 4’ center-to-center system.
- Assemble your base rails** and put them in place, marking where the holes should be dug. (A 16D nail driven into the ground through the pre-drilled hole in the base rails works very well for this.)
- Next, use a post hole digger or auger and drill holes 30″ deep. Clean the holes.
- I would now position the base rails from the steel construction kit according to the instructions and drop the ground anchors into the pre-drilled holes. Use 2500 psi concrete (ready mix bags or mix your own) and using a shovel fill in the holes.
You must wait at least seven days for the concrete to set properly before proceeding with the assembly of your steel building.
Concrete mounting:
- slab size. You should make your slab 4″ wider than the width of your steel building and 6″ longer. This is so you don’t chip or crack the edge of the slab when driving the concrete anchor expansion bolts into the slab.
- Concrete floorNote: Your flooring should be a minimum of 4″ thick. Make it 6″ thick if you plan to park large vehicles such as larger trucks or RVs. Concrete should be a minimum of 2,500 psi concrete with fiber mesh reinforcement added at the batch plant OR #3 rebar on 24″ centers. You should also consider using a 4,000 psi concrete mix in conjunction with the two additional inches of concrete if more than a normal amount of weight is intended.
- Be sure to saw cut expansion joints within an appropriate time after pouring is complete or trowel expansion joints while finishing.
Foot requirements: (Requirements of the International Building Code 2000 or “IBC 2000”)
At the same time as for the floor, you go to the perimeter footings. This is called a monolithic pour or monolithic slab. Perimeter pads must be 12″ deep (you can include the 4″ from the floor as part of the 12″) and 16″ wide. Footings shall have two lengths of #4 rebar at the top and bottom, continuous runs around the entire perimeter.
In our local area (Tempe, AZ), foundations would cost approximately $11.50 per linear foot (run).
That is all. If your building department is still using 1997 UBC (Uniform Building Code), which is the case with many of them, your base only needs to be 12″ wide. That should take about $1.00 per linear foot off the estimated price of the base. For more information on specific requirements for steel buildings, visit Absolute Steel and Storage You can find many pages of technical support information there.
** = See pictures on how to assemble your base rails here: Assemble Your Base Rails
