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Wood floor to support a car

Mark_H's picture

I'm planning to build a storage building on a sloping site with a lower level and then the main level with a wood floor. I found a great site with span tables:
What I need to know is what kind of live load and dead load should I figure if I want to store a car or tractor in the building? I'm planning on using 2x6 treated T&G boards for the floor boards.

(post #162350, reply #1 of 17)

Span tables wont cut it - You need an engineer to review a complex situation like this.

Typically, it's 50 PSF live load
i plus
150% of the higghest weel weight of the vehicle that's most likey to be in the garage placed anywhere on the floor. (Plus dead loads)

I doubt the 2X6 wod floor would hold up for long. You would probably want to pour concrete over the top of the wood floor.

I've quoted a few of these over the years, but have never seen one actually installed - they're just too expensive if they're done right.

i have
seen a couple of garages like this go with spancrete floors, though.

(post #162350, reply #2 of 17)

You have to figure garages with very liberal safety factors. Autos are live loads with special properties including the fact that they can enter at a speed and then brake rapidly-transfering that inertia to the building. Also figure for huge dead load as more often than not the place will be storing tons of stuff. Your other concern is lateral bracing and shear stress of the walls supporting it. In short, you need more than standard tables to design this one safely, get an engineer.
Also, you should figure that the wood floor will be getting wet from the car and thus should be considered a roof to prevent moisture damage to the supporting framing.

(post #162350, reply #3 of 17)

Danger! Stop!
Modern cars have a catalitic (sp) converters. The Heat from them can start a wooden floor on fire particulary if it's gas and oil soaked. In addition cars can and do leak fluids. I doubt that any building inspector would allow such a thing. In addition have you figured out how to deal with the carbon monoxide issue? Evan if you open the door before you start the car someone or something will get an unhealthy level of CO. (it settles, not rises)
I doubt that you'll ever get a 2x to ever carry the load, evan with 12 inch spacing and 2x12's spanning 8 ft. we are talking steel and spancrete here.

(post #162350, reply #4 of 17)

Wow you guys-
Calm down! How many barns have you been in full with tractor, truck and the last bailing? And who was that engineer that help design that barn before there were trucks and tractors?

Sorry I don't have the answer but this can be done.

(post #162350, reply #5 of 17)

Live load....that would be the car.

Dead load...that would be the car falling through the floor onto you.

Better leave this one to the pros.


(post #162350, reply #6 of 17)

I'm with Gabe on this one (gasp!) just cause we do it (RE, old barns), how many old barns have you seen on fire? old barns are not air tight homes so when you fire up that old John Deere there is enough fresh air to prevent someones death from carbon monoxide. Most barns were built with timbers that you would have a hard time finding today. They were built to hold a winters worth of hay not a room full of kids.
Calculate the load of an SUV say 5000# on 4 tires which have slightly less than a sq.ft. per tire contact. thats 1250 pounds per tire. Spread that over a two by four that is as close as a foot apart and you can see that a 50# load isn't going to begin to cover it.

It is done all of the time with Spancrete and steel. Give Spancrete a call and they'll tell you about what you need.

(post #162350, reply #7 of 17)

The next time you are in a barn, take a closer look at the size of the framing members that support the floor that support the tractor and the hay wagon. 8x10 to 8x12 sounds about right for many that I have seen. I checked the span tables and didn't see too much listed in these sizes. You are right. This can be done. Go ahead and wing it. The guys here are giving practical advice here. Anyone looking at span tables hoping for info on parking a car on a floor supported by 2x lumber needs to be told this is not a good idea.

(post #162350, reply #8 of 17)

I toured a house last year that had a basketball court underneath the garage. The builder used a precast concrete system with a slab poured over the top. Probably the same as Spancrete, but I'm pretty sure that it wasn't in this house. Pretty nifty.

(post #162350, reply #9 of 17)

When I was young I worked on this farm and the barn had hand-hewn 8x8 to 8x10 floor joists spanning at least 12' (a car could park in the lower level between the rubble stone foundation and the support posts)and floored with 1 1/2" oak planks (not T&G). The farmer not only parked his Ford 9N tractor in there, but he parked a school bus in the barn every day for many years. Come to think of it, how long is a school bus? The bus completely fit in the barn with the door closed and there was only one center beam running the center of the lower level so the span may have been much longer?? Of course, 100 year old oak is much stronger than the wood we hav today.

(post #162350, reply #10 of 17)

I truly don't believe any local building authority would allow construction of such a floor, mostly due to fire protection.

Scott R.

(post #162350, reply #11 of 17)

You can build a wood carport deck, but if it has potential living space attached you need a concrete or a cementiouos (sp?) fire rated membrane over a well engineered structure. You can't beat a steel frame structure for this.

(post #162350, reply #12 of 17)

Mark already identified this as a storage building. Not too many folks live in storage buildings.

In Maine there are oodles of old garages with wood floors built on piers. Joists should be sized for at least 50#/sq ft. Decking is usually 2x6 T&G pine or spruce. I've seen hundreds of bridges built of wood that have carried loads for generations. So yes, it can be done. But wisdom suggests that you think it through first.

After ten years you will discover the weak spots and wonder whether you did the right thing or not.

Right now, I am working on a home where the original builder used an engineer to design ther garage floor over a workshop/storage space. Joists are 2x12 @ 12"oc spanning 12'. Decking is 2x4 PT on edge. Owner reports that rain drips off the cars, and runs down into the storage below by slipping through the joints. Dirt does the same.

(post #162350, reply #13 of 17)

As living space I mean habitable space, the terms are interchangeable for fire code, and in the eyes of the building dept. a storeroom can quickly become a workshop, as you pointed out. I grew up spending hours in dad's workshop under the wood-framed garage at our house and it is still there. But you can't get a permit to build that now, not here anyway. By the way, I believe it was 2x12 redwood planks over 2x12 fir joists, 16" o.c., 8' span over 6x10 fir beams with 4' spans. Creaked like a mother though.

(post #162350, reply #14 of 17)

rumble creak

letting the poet out

(post #162350, reply #15 of 17)

Just was in an Amish Garage for sale...$3500 delivered and set on site. Floor was 2x4 PT joists 12" OC. The deck was 3/4" PT plywood. The owner of the Sales lot had his Bugatti parked in it when I checked it out. The floor held the tire weight with no signs of strain. He has sold these buildings now for years and years. It is placed near the ground with no one able to be under the floor in danger.

near the stream,


(post #162350, reply #16 of 17)

How much does an elephant weigh? I saw the add for TJI s they had an elephant walking on the floor and said that it did not make noise or move. So if you have to make it out of wood Give them boys with the elephant a call.

(post #162350, reply #17 of 17)

I'm planning to build a storage building on a sloping site with a lower level and then the main level with a wood floor. I found a great site with span tables:
What I need to know is what kind of live load and dead load should I figure if I want to store a car or tractor in the building? I'm planning on using 2x6 treated T&G boards for the floor boards.