Tag Archives: concrete floors

Can I Put a Pole Barn on Asphalt? ~ Dear Pole Barn Guru

Ask The Pole Barn GuruDEAR POLE BARN GURU:  I have a full size tennis court, we want to put a pole barn on the tennis court (we don’t play tennis) The barn would be 30 x 60 obviously leaving an asphalt perimeter larger than the barn around the barn – how would you seal the edges where the barn wall will meet the asphalt to prevent water intrusion? TENNIS ISN’T OUR RACQUET

DEAR RACQUET: I’m there with you, as I don’t play tennis either.

The nice big flat paved area where your tennis court is, makes for a very appealing location for a new pole barn. After all, it seems to be flat, and why not put the asphalt surface to good use?

Over the past three decades, I’ve seen numerous pole buildings constructed on top of existing asphalt, in situations very much like yours. And all, to the best of my knowledge, have been fraught with challenges.

First challenge – never is the “flat” tennis court actually level. This means a decision to either place the pressure treated splash boards to a level point (recommended) and then somehow fill the space in below them with something or to place the skirt boards with the contours of the asphalt (please do not even attempt to do this).

Second challenge – Assuming the splash boards were set to level, custom ripping pressure treated “filler” boards to fit between the splash plank and the asphalt is neither fun, nor easy. Plus, gaps will still exist.

Third challenge – and the root of the question, “how to seal the edges”? I’ve seen a myriad of products used, all asphalt based – none of which did a satisfactory job, over time. Asphalt expands and contracts greatly with heat and cold. The wood splash board does not. After a few hot/cold cycles, whatever seal was originally created, no longer exists and water is now flowing into the pole building.

There IS a solution, which will result in a far better outcome, as well as a much better floor than the asphalt tennis court.

Locate four corners on the asphalt at least four feet greater in width and length than the proposed building. After making sure the diagonal measures between the corners are equal (e.g. the market out location is square), snap chalk lines on the asphalt to follow the perimeter created by the corners.

Rent a walk-behind asphalt saw with a “wet blade” and cut along the chalk lines. The area inside the cuts can now be removed (requires a loader with a bucket and a dump truck to haul off the debris).

The building can now be constructed (to level) centered within the cut out area, and a concrete slab floor poured inside. Any water runoff from the surrounding asphalt can be captured in the area around the building. Fill in the space between the concrete and asphalt (outside perimeter of the building) with gravel.  This will allow the water to disperse.

The concrete slab can be set so top of the slab is higher than the surrounding asphalt, also minimizing runoff threats.

Bonus – concrete floors are much easier to clean and maintain, and ever try to run a creeper over asphalt?

Concrete Slab Calculations

One of our Building Designers asked me the other day if a 10% “shrink factor” should be used when advising how much concrete it takes to pour a concrete slab on grade. This particular Building Designer “in a previous life” had been a building contractor.  It had been his practice to always order 10% more concrete for a pour, than calculated! In my neck of the woods, concrete is pretty darn expensive. I only want to order what is actually needed to do the job.

First, let’s talk about concrete slab thickness. Concrete floors and slabs on grade are called out by their “nominal” thickness. Just like a 2×4, a four inch thick slab is only 3-1/2” thick. This is so the edges can be formed by using a 2×4 and the area to be prepared can be graded off the same way, by using a 2×4. The same goes for a six inch thick slab, being actually 5-1/2” thick.

Second, let’s do the math. Concrete is purchased by the cubic yard. A cubic yard would be three feet in all directions, or 27 cubic feet. If pouring a four inch thick slab, we need to spread this one yard cube, across four inches of thickness. As four goes into 12 three times, we can multiply 27 by three and get 81 square feet four inches thick.

For a nominal four inch thick pour, I would divide the square footage of the total pour, by 81 to get the number of yards required. Let’s consider a 24’ x 36’ pole building. 864 square feet of area divided by 81 equals 10.67. Round up to the nearest whole yard and order 11 yards.

Hold it…..but a four inch thick concrete slab, is only going to really be 3-1/2” deep in real life!

In an “ideal perfect world” a 3-1/2” nominal thickness floor would allow 92.57 square feet of area to be covered by a yard of concrete. However, there is just no prepared site which is perfectly level and compacted so tightly as to not have some of the concrete going into making it level or filling voids in the fill area. The concrete mixture also includes water, which will be absorbed into the surface below or evaporate as the concrete cures.

The summary is – for a nominal four inch thick pour, divide area by 81. For a nominal five inch pour divide by 65, six divide by 54. As long as a good grading and compaction processes have been followed, these numbers work every time to give you “just enough” for your concrete slab.