Load Bearing Garage Floor over a Basement

[marrt]

I want to build a detached garage with a basement. For reasons I won’t go into here, I would like to keep the visible footprint of the garage as small as possible while having the most space available. One idea is to build a 24’ X 24’ garage with a full basement. However, I would like the first floor to be fully load bearing so I can park my truck on the first floor and my tractor in the basement. Although this design would suit my needs well, it seems like the design would be prohibitively expensive (would probably need a significant amount of steel, would need an architect to draw up plans, etc…). Any thoughts? Anyone tried to build a load bearing garage floor over a basement?

 

[MossRoad]

Our neighbors had one when I was a kid. After 25 or 30 years, it started leaking and crumbling. Something to do with salt and the rebar in the slab.

It also might not be legal in some locations, so check with code. Fumes, vapors, explosions, etc...

 

[Anonymous Poster]

I can show you one that is 50 years old, and has and still will support a D-8 Cat.
Truss construction under the floor, 6" of concrete with plenty of rebar, with all the air vibrated out of it during the pour.
An alternative, in today's world would be to install precast slabs for the floor and install a membrane prior to pouring the cap over the slabs. That would probably be less costly than pouring your own slab, and the slab engineering would be free from the precast provider.

 

[Anonymous Poster]

When I built my house with an attached 22X24 garage I used prestressed concrete on the floor so that I could use the space under the garage to store my tractor and lawn equipment. The only problem that I have had is that in the winter, as snow melts from the vehicles on the upper level, water sometimes drips through the hairline cracks that have developed at the seams of the prestressed panels. I think the problem could have been eliminated if I had installed a membrane material before I poured the 2" topcoat of concrete.

I highly recommend prestressed concrete for the application that you are considering.

If you want more information or if you would like to see some pictures, let me know.

John

 

[Hoeman00]

I built a 10'x14' safe-bombshelter in my basement
when I put addition on house.
Used 12 courses of 12" block and 8" for top course.
Then from local steel supplier got steel decking that
is used to pour concrete on.
The 4" ledge gives good places to let cap sit on.
rebar every 12" both directions into 8" block then some
concrete mesh thrown in.
I poured 8" thick slab.
I put a beam and jacks under roof while pouring and took
out the next week.
All the cores are filled w/ rebar, old carbide cutters and
inserts and concrete.
This should give robbers a tough time breaking in.
W/ size u are doing u will need someone to design the
beams and location.
Look at old bank barns w/ wood floor and timbers
and people put loaded semis in them.

 

[Egon]

It should not be a problem. Use precast slabs that have been designed to meet applicable codes.

Egon

 

[marrt]

John, I would like to see a picture if you don’t mind. I’m not familiar with pre-cast or pre-stressed concrete. Is this stuff manufactured under controlled conditions and then delivered to the site? I’ll call the concrete company and see if they know of a supplier the relatively close (I live if the sticks so close is definitely relative).

 

[Anonymous Poster]

Mart... Attached are two pictures from under my garage. The type of panel that I have is called double T. It will span up to 60 feet. Each panel is 4 foot wide. The product that I have is used in parking garages and bridge construction. They also had a product that would span 40 foot and it was a lot thinner. I didn't get it because it was a lot more expensive than the double T. I built my house 23 years ago, I'm sure there are more and better products available now.

John

 

[Anonymous Poster]

Another picture.

 

[Casimir]

Marrt --

Not sure where you are located in No. VA, but Smith Midland on Route 28 south of Manassas manufactures prestressed concrete. My son-in-law worked for them a while as a structural engineer before he opened his own engineering firm. They could probably give you advice on what you would need and a quote on price and delivery.