“Hello, I found where you had answered a question about a wood floor in a garage while I was searching the web asking “Wood floor in a garage?”. Let me explain, I am a disabled veteran living on a fixed income. I have a blood cancer as a result of being exposed to the toxic smoke of the burn pits in Afghanistan and Iraq. I was told that once I started treatment I would live 7 or 8 years, 10 if I am lucky, I have been on treatment now for about 3 years. I bought my farm from my dad. I have a double wide home that is set up on a basement (with garage door), the problem is it is only 7’ tall with a 6 and ½ ‘ door. I don’t have anything that fits. I plan on building a 24 by 24 workshop/garage. I will build it much like a pole barn, for the simple reason I can build in phases. One pole at a time so to speak, as money allows. I am looking at wood for the floor, I know in the really old days wood floors were common. The problem I am concerned about is the weight limit. I have a Mack Truck that was given to me, basically a toy, but a subsidiary of Mack Trucks rebuilt it so it is real nice. I need the floor to be able to support this. My plan is this: 2×8 treated floor joist, 12” on center. Topped with 2×8 lumber, then topped with ¾” T&G plywood – to get it smooth. To be honest I will probably have treated plywood on the bottom of the joist and fill in between the joist with what they call around here waste rock. Then top it off with the 2×8’s and plywood. The joist would run from front to rear, allowing a chance for the load to be right on a joist. I expect it would be about a 10,000 to 12,000 pound load spread on 6 tires, I am guessing about a 10” x10” patch for each wheel, the heaviest load would be the front wheels. I am not asking for official specs, just a professional opinion. I realize cost wise it could probably be built with concrete cheaper, but I have to build it a piece at a time, and to be honest it may never get finished. Thank You.”
How To Properly Design a Barndominium Wood Floor Over a Crawl Space Reader JERRY in HAWESVILLE writes:
“If one were to build a post frame home on a crawlspace and the floor joists were sitting on a 3 ply 2×10 center beam on post spaced 8-10 feet apart, how does one support the joists at the outer walls? Do you need another 3 ply beam on each side and how would you attach those to your posts? If you could show a diagram, that would be great. Thanks.” Well Jerry, a simple answer is yes, you need to support floor joists at the exterior wall. Beyond this things begin to get more complex and should only be done with a Registered Professional Engineer being involved. Let’s begin with your interior floor beams, we will check for a beam spanning 10′: fb: bending stress from live/dead loads P = (D + L) = 10 psf + 40 psf = 50 psf W = 50 psf * 8′ / 12 in./ft. = 33.333 pli (8′ is tributary area being carried by 3 – 2×10 #2 SYP members) M = (33.333 pli * 120″2) / 8 = 60000 in.lbs S = b * d2 / 6 = 3 * 1.5″ * 9.25″2 / 6 = 64.17 in.3 fb = M / S = 60000 in.lbs / 64.17 in.3 = 934.99 psi 934.99 ≤ 800 x 1.15 (Increase for repetitive members) so over stressed in bending by 1.6% Not a very practical design solution. If beam span is reduced to 8′, then allowable tributary area could be increased to 12′ (e.g. 6′ on either side). Moral is your proposed 3 ply 2×10 beam is probably not a best solution. Beams also need to be checked to meet Code required deflection limitations of l/360 where “l” is the span of beam between supports. In this instance, bending will dictate design. Hopefully this alone shows a fully engineered solution is best, as an engineer will confirm all needed grades and dimensions, as well as best connection methods. He or she will also design column footings to be adequate in diameter to properly distribute added weight (both live and dead loads) being added due to your floor system.