Residential Garage on Stud Walls 1

[aseeng]

Are there any guidelines for supporting a garage floor on stud walls? I have a 19ft x 12 ft. garage floor using 14" LVL's, 1 1/8" plywood and 4" topping slab. We have done wood floors many times and APA has some good tech info on these. I can't find any literature on supporting this kind of floor on stud / plywood shear walls and I am debating whether it's a good idea.

Thanks,

 

[jayrod12]

So is this a second floor garage? I don't understand why you would support a garage on wood. If you are going to pour 4" of topping why not just do a slab on grade?

 

[manstrom]

I want to say that there is something that prohibits wood studs from supporting concrete slabs, but I'm not sure.

Personally, I would never put a garage on a wood floor. Have you checked for 3000# point loads required by code? Even with concrete, it will need to be reinforced. I just did a garage on metal deck and we needed a 5" slab. We recommend strongly against these at our office. If we need to do them, typically we use metal deck with a thick slab on steel beams or concrete walls. Make sure and consider salty snow dripping off a warm car for corrosion.

 

[aseeng]

The house is a walk out basement where the garage is at the main level (high side) and sits over the basement living area. We utilize APA TT-071B for guidelines on wood floors. We agree, waterproofing is critical. We are comfortable with the strength and performance of the wood floor and would typically support these on concrete walls. This arrangement however, will result in (2) add'l 10ft interior concrete walls. I want to tell the contractor / architect that either the code specifically prohibits stud wall support or doesn't. Or are there case studies that show this is not a good idea?

 

[jayrod12]

I think in the CSA S406 in Canada there are details for supporting a concrete slab on wood walls. Might be a place to start.

 

[manstrom]

It may be doable. Another thing to consider is the lateral loading from the car accelerating / decelerating. What if junior mashes the gas in Dad's vette and backs out of the garage at 0.5g? What if Mom slams on the brakes of the minivan to avoid hitting the cat at 1.0g?

I don't know what the details look like, but make sure it considers all the load effects.

When working with untested construction methods, it's not the devil you know, it's the devil you don't know.

 

[msquared48]

Wood Supporting Concrete Helpful Member!(3)

thread507-292879

Mike McCann, PE, SE (WA)

 

[jdgengineer]

I'm not aware of this being a specific code violation. I have seen elevated garages fairly commonly on hillside lots. We also do them with some regularity where we have a full basement beneath the house. I do agree that you need to think about lateral loading, etc. Although typically, we have return basement walls that would alleviate the concern.

For the design of the framing we typically follow a technical bulletin put out by TrusJoist (TB-105). One very important aspect is not to use TJI joists (which you are not using) as they won't be capable of resisting the concentrated load.

I would check the wood stud wall for the concentrated jacking load to verify that the studs are adequate. We typically frame this wall out of 2x6 and install blocking to brace the studs (in addition to any sheetrock, etc.) I'm not aware of any problems we have had with these garages. It's potential that the wood framing will creek as a car drives over it as the wood shrinks. I think using engineered lumber would help this somewhat.

Waterproofing is hugely critical in these installations. We typically install a water proof membrane between the concrete and the subfloor and use PT floor plywood.

IBC Section 2304.12 states that wood members need to be checked for creep loading where the non-structural concrete floor surface exceeds 4". I typically check it here anyways, but it doesn't usually govern as the members are generally quite stiff in order to meet the jacking load design.

Given the choice I would prefer metal deck and concrete, but have seen quite a few of these out of wood.

 

[aseeng]

Thanks for the replies. The lateral loading is an unknown to me and was hoping to find that guidance published. I suppose if we use a 1.0 g loading on a 6000 lb vehicle or 3000 lbs / shear wall we can engineer a robust solution. And thanks for your experience jdengineer as it sounds like this has been done before (be it good or bad?).