View Full Version : can this wood floor in a garage support a vehicle??

04-26-2004, 03:43 PM

I have a garage with a wooden floor (storage underneath). It has 2x12 joists with 12" centers and plywood over it...would this be able to support the weight of a vehicle?? if not, is there anything I can do so that the weight can be supported?

Thank you kindly!

04-26-2004, 05:02 PM
I have no idea - but I personally wouldn't trust it. All it would take is a knot in the wrong spot and your storage area has a new and very large semi-permanent fixture. I'd have an engineer look at it - I may be overreacting.

04-26-2004, 05:58 PM
In my humble opinion, I would say that as long as the floor has 2 layers of 3/4" plywood, it would be safe for the average car. One layer of plywood just probably wouldn't support the weight that would be placed on it between the 12" span of the joists.

In addition, the second layer of plywood should be staggered from the first layer so that no joints are lined up with any that are below it.

04-26-2004, 06:45 PM
You're probably right. A design we had done for supporting a 2700lb lift on an elevated slab would require 2x material at 12" o.c. with 2 layers of plywood. So yes, I agree, for the average car the plywood would probably be ok. Comparing that lift to an average car - Toyota Camry weighs 3000lbs. The biggest difference between these 2 scenarios is that on my elevated slab I have the slab that's also supporting the 2x material.
You make a pretty bold statement to be honest - especially considering that no span was given on the joists. They could be spanning 25' or more and 2x12's are typically only rated at 18'. With 12" o.c. you could probably get that to 22' or so BUT remember that's only for typical live and dead loads on a residential floor - around 50psf.
My recommendation - contact an engineer and pay the 200 to have them look at it and give you an answer that you can allow you to sleep at night.

04-26-2004, 09:09 PM
I agree completely on the engineer having a look-see at the situation. It didn't even dawn on me that the garage could be a two-car (or bigger). I just assumed it would be a single-car garage with the joists running the short direction.

I'm not even sure, to be honest, who in their right mind would ever make a garage floor out of wood in the first place, especially an elevated one...lol

rbirmingham, do the right thing...hire an engineer to take a look at it. It might be ok as it is, or it might be something as simple as having to double up the 2x12's or maybe just adding joist hangers to the ends of the joists. Don't take any chances on this one.

04-27-2004, 12:08 AM
You're absolutely correct - it could be as easy as adding joist hangers or maybe even mid-span blocking. I suppose the worst case scenario would be a strip footing or something like that with a pony wall down the center of the garage - could cut down storage.
Anyway - good luck with this and let us know if you talk to an engineer and what solution there was.

04-27-2004, 03:06 AM
thanks for the replies! the span is actually about 14 feet (single garage)...i think i will call a couple of engineers to see what they say.

05-27-2004, 08:08 AM
I have an outside workshop that is pier and beam (24x30) and I had the same question. I found this, relating to the plywood floor:


But it doesn't talk about joists or beams. I've decided to pour a slab inside the building instead, partly because my garage floors tend to get soaked in grease, gas, and oil.


05-28-2004, 10:03 AM
My only advise to you sir is keep this floor well protected from any water and inscects. I would like to know who built it or better yet thought it up.

05-29-2004, 11:24 AM
I just built a wood floor in a garage this winter. The engineer called out I-joist 900s_1178 @ 12" centers (308in allowable span @ 12in), our span was 10ft. between beams. The joists also ran parallel with the garage door. A 3/4 tongue and groove sub-floor was installed and then 3x6 double tongue double groove car-decking was screwed down with 5in screws @ 12" centers.
The owner parks his 26' motorhome on the floor and 2 vehicles. No creaking, sagging or cracking.

05-29-2004, 12:01 PM
Whew... not for this kid.. concrete all the way :)
Engineer or not.

05-29-2004, 03:28 PM
It turned out looking nice, but like you, concrete for me also. :wink:

05-29-2004, 07:49 PM
I'll bet it is.. plus the additional storage space you could get is always helpful.

05-30-2004, 09:47 AM
The customer has a 14' crawl space under his garage floor. :D

05-30-2004, 12:58 PM
Wow.. I could setup a whole workshop down there.

05-30-2004, 09:52 PM
Thats his plan, he's going to grade it out a little better and pour some concrete.

05-31-2004, 03:15 AM
When we talk about extreme loads on traditional wood frame floors there seems to be a common concern that we address - the ability for the floor assembly to carry a given load. What we don't seem to address is the fact that these loads must be followed to their ultimate destination - the footings and bearing soil.

How much bearing do you have at the end of the joist. The minimum for most building authorities should be in the neighborhood of 1-1/2". But remember that these minimums are determined at the normal maximum loads - not vehicle loads. Sure, the floor assembly may hold up the loads but the tails of the joists may be crushed or perhaps the top plates.

And look at the walls supporting the structure. Is it wood frame? We use a double top plate on a bearing wall so that we do not have to concern ourselves with lining up the joists with the wall studs. But, again, this standard was developed to accomodate normal floor loadings. Parking the family Buick in the livingroom does not constitute normal floor loading! You mave have to line up the walls studs and joists or perhaps add a third or fourth top plate.

What about the axial loads through the studs themselves? Do we have to add another row of blocking? Or perhaps two? Perhaps both side of the wall will have to be sheeted. Who knows? I sure don't!

Yes, use an engineer, most definately!

05-31-2004, 08:16 AM
Hopefully an engineer would also consider the unusual lateral and sheer forces exerted as the vehicle drives onto the floor and stops.


05-31-2004, 08:35 AM
Thats one dynamic I never even considered!!!!! Could you imagin the load on the walls if you pulled into the garage and slammed on the brakes??? :shock:

You could bring down the whole end of the house.

05-31-2004, 03:04 PM
The joists have 5"1/2 bearing at the ends of the joists and the same every 10' with 6x12 beams. The beam lines and joist ends are blocked and have web stiffeners. The joists were installed with their tops flush with top of mudsill and the 3/4" sheeting ties into the mudsill along with the 3x6 T&G car-decking. The concrete foundation would have to be pulled over before the building would come down. My worry would be hitting the gas instead of the brake and going through the end wall that is 14' in the air.

05-31-2004, 07:53 PM
LOL.. be tough to explain to the spouse.

06-02-2004, 09:15 PM
LOL.. be tough to explain to the spouse.

My worry would be with the spouse.

06-03-2004, 04:09 AM
LOL.. ok let me clarify (I was trying to be politically correct)..
be tough to explain to the man of the house.

06-04-2004, 11:54 PM
Now you are catching on. :) No PC here. :D

07-09-2004, 03:41 PM
I have a similar situation. I have a 24x30 workshop that is built on piers. 10' spacing in the long dimension, 12' spacing in the short dimension. Floor joists are 2x8, 24' long, hung with joist hangers. I want to be able to park a car in it. I was originally going to fill it in some and pour a slab but the cost has me considering other options.

My thought was to remove the plywood flooring and pour some supporting concrete beams under the joists. 2 along the wall to support the ends of the joists, and 3 or 4 more evenly spaced between them. Then every joist is supported, and the maximum span would be 4 or 5 feet. Reinstall the plywood and add a second layer such that the seams don't overlap.

I think the worst case would be a 5000 lb tire parked directly over a joist, with the tire in the middle of the span. Will the 2x8 support that load over that span? Is there a table of beam loading that has this answer?