Plywood Load Ratings

[Dennis Putnam]

I am in the process of customizing a trailer for BBQ competitions. As such, weight is critical. Since the interior is going to contain living space it will be air conditioned so I need to insulate. I plan to use foam panels between furring strips over the sub-floor (3/4" ply) and then cover that with plywood and probably peel and stick tile. The main consideration is that I will be rolling a 750# smoker into the trailer for transport so the floor needs to be capable of supporting that, at least from the tailgate to the axles where the smoker will be secured. The question is what is the minimum thickness of plywood that I can use? I am hoping I can use no more than 1/2" because 3/4" will add too much weight. Ideally I'd like to use 1/4" since other the then smoker, the rest will just be supporting people walking and standing. I figure the plywood and foam together can support that much. I would hate to have to use 2 different thicknesses needing some kind of taper for the transition but that would probably be better than a 1/4" step. In any case I am pretty sure I can't use 1/4" under the smoker path from axle to tailgate but can I get away with 1/2" and 1/4" everywhere else? I guess I'm looking for a solution that provides minimum weight with the maximum R value. Because of the harsh exposure, I don't think insulating the underside of the sub-floor is practical so I don't see an alternative to adding the interior floor.

[cody michael]

can you put a wide "furring strips" under where the wheels of the smoker will be? placing weight directly onto the subfloor. how big are the wheels, I think it would make a big difference if they were car tires, vs casters.

[Dennis Putnam]

Hmmm, good idea. I would need to make sure the smoker stayed over those when moving it. The wheels are 10" diameter and about 2" wide. I don't know what the R value is for furring strips but I think if I lay out 3 or 4 on each side to make tracks, then 1/4" ply would work. I doubt that 6 or so inches under each track without foam would make that much heat loss difference. I could get different color peel and stick tile to mark the area. Thanks.

[Curt Harms]

Dennis, I assume you've thought of this but I hope you have at least 850 lbs. ahead of the axles when ready to head down the road. I've had experience with bumper pull trailers improperly loaded. I don't recommend it. For the surface exposed to the road, would something other than plywood be longer lived? I'm thinking of something like the panels we have on our garage door. Aluminum skins with corrugated something - cardboard & epoxy? - in between. I paid $20 each for them but that was close to 20 years ago.

[Peter Quinn]

I did a few basement remodels with rigid foam under plywood, recommended was 2 layers of 1/2" ply over the foam glued and screwed together, cross banded. No stringers at all, screw right into the substrate. The thermal bridge reperesented by the sleepers is a problem for insulating. You want more than 1/2" of plywood over any foam where you are going to walk or roll machines.

Not sure how conducive it is to living space but lining the floor with a sheet of diamond plate sure would add to its durability.

[Bob Grier]

Dennis, If I was doing this with weight being a critical criteria, I would look into diaphragm type construction using very dense rigid foam with skin on top and bottom. Bottom skin selected for exposure to highway environment like previously mentioned. I would probably explore panel manufacturers for an off the shelf product designed to meet my needs. If I was really into weight control I would explore having a panel designed using carbon fiber on the skins and vacuum laminate them yourself. My son did this for floorboards in an airplane but he had some help. I suppose I am stating the obvious but, for thin skin like 1/4" ply on top, you will probably need a very dense rigid foam to resist the puncture or point loads.

I think it possible the expense of building panels yourself will be high and technical know how hard to acquire. My guess is that standard frame construction with the heavier weight will be the most cost effective, even if it requires stronger axle and trailer to carry the load.