I am new here so please let me know if this topic is in the right place or maybe belongs at another forum.
I am getting ready to build a garage/shop (28′ deep x 34′ wide) with vehicles above/shop below (this due to driveway costs and other site considerations). Under consideration is the floor system for vehicles. Conventional approach is concrete slab over steel decking with reinforcing in the deck. Even with composite steel decking (the stuff that grips to the concrete and becomes part of the reinforcing system) the cost of concrete, steel, and a support structure adequate to the task of vehicles and 50,000 lbs. of concrete and steel is pretty darn expensive (approx. $6000 materials).
A wood deck with wood joists looks like it can work and will cost a lot less. Decking would be 1″ or 1-1/8″ T & G Advantech or plywood over TJIs on 12″ or 16″ centers with steel support beam down the center. One of the big advantages is supporting only vehicles and 8000 lbs. of wood structure rather than 50000 lbs. of concrete and steel.
The materials cost looks to be slightly more than half for wood compared to concrete. Added benefit is that the wood version seems easier to build. The steel/concrete approach seems like a lot more work and expense. The engineer at the local lumber yard says this will work and he will certify it.
The big issue with wood seems to be how it will fare with wear/tear of vehicle traffic, drainage of slush, mud, water brought in by vehicles, etc. Advantech’s specs say that their product should not be painted/sealed so that’s not an option.
Am I nuts?
Thanks for your thoughts.
Replies
<<Am I nuts?>>
Only if whoever built most of the service stations in the Northeast in the 1940's and 1950' were nuts too.
Rather than plywood, what about car decking? It's a dimensional lumber designed for just such a purpose, about three inches thick as I recall. Some has a double t&g profile so it's tight. You can also buy it treated for fire or rot.
-Albert Schweitzer, philosopher, physician, musician, Nobel laureate
(1875-1965)
I would think it is a fire hazard.
John
Depends. Exposed light framing is definitely a fire hazard.Faced with 5/8 Type X rock it's not so bad.Faced with two layers of Type X properly installed and taped so there are no exposed voids and no penetrations, it's amazingly safe.If he builds it of heavy timber to the requirements of Type IV Mill construction then it has one of the best fire ratings that can be achieved.
Success is not the key to happiness. Happiness is the key to success.
-Albert Schweitzer, philosopher, physician, musician, Nobel laureate
(1875-1965)
Are you saying to put 5/8 rock on the deck? My reading of the initial post is for the floor on which he parks cars to be wood (unless I misundertood). I would doubt that that would comply with fire code.
John
The rock goes on the underside of the deck framing.The idea behind fire rock is to not let the fire get into the voids in the light framing (if that's what he uses).The top side of the deck needs to be structural, which is why I think car decking would be the way to go. It's tight, resistant to everything, and the load bearing is pretty good. That's what it's made for. As long as you don't let fire get in underneath, it ought to work great.
Success is not the key to happiness. Happiness is the key to success.
-Albert Schweitzer, philosopher, physician, musician, Nobel laureate
(1875-1965)
Thanks for clarifying.
I have built such a floor in a garage the cars havent fell through yet it was 7/8 t&g with 1.5" pine ontop just for looks not for strenth it was a pretty floor they wanted.
nothing was ever mentioned about fire .
i just think of all the barns with all that hay and some were made with floors to hold many horses .so i see know prob
Good idea but....
You need to have a non-combustable floor (code requirement). That leaves pretty much concrete as the floor surface.
I did hear rumor of a wood deck that was surfaced with cement board but do not know any details of it.
bt
Not only did we use wood for the structure of the garage floor, but we also used wood for the walls that supported that floor. It was an unusual hillside wood foundation system.
Anyway, the key for us was to use 4 beams of 4-2x12 each about 4' o.c. going the direction of the car tires and roughly under the car tires (16' long). These became exposed beams in the rec room below the garage. Above and perpendicular to those beams were 2x10's 12" o.c. with 3/4" ply on top. Then vapor barrior, then 2" of poured concrete. The concrete is there both as fire protection and to help "span" the 10" of plywood between the 2x10's.
We had an engineer sign off on the system. As I recall the biggest two issues were fire protection under the vehicles and a point-load requirement of 5,000lbs . That point-load requirement is what will really required an engineer. You won't find that in a span table for joists or decking.
Even with the 2" of concrete on top the system is much lighter than the all concrete alternative, especially when you consider our wood walls vs. void-filled 12" concrete block or some other concrete wall option.
Even with the engineer's approval, I was a little nervous about having a car parked over my head until we had the sheetrock delivered to the site and had it all layed in the garage right where the two cars would go. 20,000 lbs of sheetrock caused no measurable deflection in the floor. After seven years parking cars there there were only the slightest hairline cracks in the concrete (fiber-embedded).
i think I'd look at the concrete over wood deck... lightweight concrete... aprox 2" as was quoted... only looking at 10yds or less but i'd still think thats $1k right there...
what might save you some is the big steel.... steel is crazy right now and prob won't get better... it's what fuels china..... I'd be on the lookout for some used big steel... usually 1/4 of new and thats still pay'n 5x what they'd get for it scrap...
pony
Provided you get the strength and low deflection, how about putting down ceramic tile with a waterproof underlayment such as Schluters Ditra? It would help with the snow/water/slush/grease/fire problems. When used with Kerdi band it is a waterproof system. Just may to provide a slight pitch for said water to drain out door way.
How about using pre-tensioned hollow core concrete panels covered with a skim coat of concrete, similar to those used in commercial structures. They can be engineered for clear span of your garage and placed above/on top of the foundation. We have built several condos with this system and the fire resistance is built in.