Basement under garage, Part II

[Zone_V]

First of all, thanks to everyone who took time to give their input.
All the responses got me thinking (uh-oh) that if it's not an essential idea to slope the floor to a drain....would the floor necessarily have to be concrete? Keep in mind this is a one-car garage, probably sixteen foot wide span. How about just using the appropriate sized laminated veneer lumber beams or engineered wood "I-beams", covering these with glued and nailed 3/4" t&g plywood, and then some sort of water-resistant flooring material, such as vinyl? When the vinyl started to deteriorate from road salt, water, wear, etc, just replace it.
Your ideas on this possibillity would be much appreciated!
John

 

[Bob_Skurka]

Engineered lumber is capable of taking amazing loads, but I think you will find that a simple layer of 3/4" t&g plywood flooring won't be up to the task. Maybe if you double up the plywood and make sure the seams are staggered. A structural engineer needs to take a look at that issue. Plywood is capable of deflecting loads and has some amazing shear strenght to weight ratios, but we are talking about a vehicle that weighs several thousand pounds resting on 4 tires, each of which will have a contact surface area of perhaps 7" by 4" and so each of those little 7" by 4" areas will be holding roughly 1000# of weight (assuming 50-50 weight distribution of the car which is actually highly unlikely so it is reasonable to assume that 2 wheels will hold 800# while 2 will support 1200 for our theoretical car).

The plywood might be rated to hold 1200#, but what you will have to deal with, in the case of the plywood floor is that it will have to support that load over a couple of decades and with humidity changes. I suspect you will very quickly develop 4 low spots.

You will probably be looking at placing the engineered lumber below the floor on 12" centers as well.

This is not insurmountable. It is an engineering issue. Also, I like the idea of the sheet vinyl floor, but I would make sure that it was seamless so there was no place for water to seep down to the plywood. You might want to pony up the added cost of using "marine grade" plywood as the epoxies used on marine grade are more resistant to water and humidity.

 

[Junkman]

Garages must be fireproofed.... all exposed lumber must be covered with non combustable material... this all applies if the garage is in or attached to the home. If it is unattached, then it doesn't have to meet this requirement. Since a lot of people here want to fight over generalized statements, check with your building department to assertain the specifics of the code in the jurisdiction that you are building. There might just be a couple that don't follow the NFPA codes and allow unsafe building practices.. /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

 

[Inspector507]

Our local building code only requires that the portion that connects to the house be covered with ½" gypsum (drywall). The rest of the garage can be exposed.
BTW, ½" gysum is not fire rated.

 

[Bob_Skurka]

Our code requires the common wall(s) be covered with fire code approved drywall on any connected garage.

 

[jim_wilson]

This is very possible. Look at the Weyerhauser site for the TrusJoist products. They have tables detailing the load carrying capabilities of the different types of I Joists they manufacture. A properly designed floor would more than support even a heavy car. Think about how much a bunch of people standing in the same area as a car or a heavy waterbed is going to weigh and a car is right in there at the same weight. Instead of using plywood I would use Advantech - it is semi waterproof and they make it in a 1 1/8 thick version that would probably work better for a garage floor. Also keep in mind that you could still pour a concrete floor over this setup - it is very common to do this in cases where people install the radiant floor heating setups.

 

[Junkman]

water beds don't put much of a load on a floor, because the load is spread out over a large area. Most floors are designed for a load minimum of 60 pounds per square foot.

 

[boustany]

The problem would not be the loading (which can be engineered around) but other safety related issues such as (noted by Junkman) fire (drywall may be ok - provided there are no other paths for the fire), oil/gas/exhaust leaks, and so forth.

Remember a car is a heavy thing full of all kinds of * very * flamable and/or toxic chemicals and bits. Ever seen a tire burn? /forums/images/graemlins/shocked.gif

I doubt if you could get a wood floor garage past any building inspector, let alon insurance company.

 

[Dave___in___CT]

Hi...


Using all rough sawn lumber may fit the bill too...

Plenty of barns with wooden support beams and flooring with tractor's in 'em...


Dave...

 

[boustany]

The tricky bit is that this is a house, not a barn, residential building codes tend to protect peoplem, and are picky about these things.

 

[Bob_Skurka]

I mistakenly thought this was a freestanding garage. In my area, as I outlined above, the common walls must be firecode drywall. But we are really talking about a floor here, I would wonder if the building code in your area would allow for a NON-fireproof flooring material in the garage. I suspect it might not. You may need prestressed concrete panels for the floor material to suit codes even if wood is possible structurally.

 

[jim_wilson]

I may have missed it but I didn't see anything in your post indicating whether or not this structure was attached to your living quarters or not. If it is attached to your living quarters you can bet that the floor and walls will have to be fireproofed in some way or another. 5/8" sheetrock is called " fire rated" . If you look on either of the web sites below you will find a wealth of articles on home building and there is sure to be some info in there that will help you decide which way to go:

Fine Homebuilding

Journal of Light Construction

Weyerhauser Trusjoist

I used the Journal of Light Construction site to figure out a bunch of the engineering when I added a second floor to my house. I used the Trusjoist system for the new floor and can tell you that it is great to work with. I know I have seen installations where this system was used for a garage floor. In most cases however a layer of concrete is laid over the floor system for the garage floor. This both gives the floor some fire resistance and it also helps spread the point load of the cars sitting on it across the floor joist system. If you have a good lumberyard near you Weyerhauser in most cases will do the actual drawings for the floor system you are going to put in place and specify the correct pieces to use. I can also tell you from first hand experience that fireproofing the structure with concrete on the floor and at least 5/8" sheetrock is going to be well worth the money if something bad happens and you actually have a fire. I have a few firefighter friends and one of them actually had a fire in his own house. Once a fire starts and gets going it goes QUICKLY. Proper construction however can turn what might have been a pile of ashes and cinders and rusting car parts into a big puddle of water and some cleanup after the fire dept is gone. If you sheetrock with at least one layer of 5/8 - preferably a layer of 5/8 and another of 1/2" and then do a plaster wall you can expect the structure to stand up to any reasonable fire long enough for the fire dept to get there and prevent any real damage. Again - look at the JLC site - there are a number of articles in there about building fire resistance into wood frame structures. I believe the Weyerhauser site also has recommended procedures for fireproofing their floor systems also.

 

[yooperdave]

water beds don't put much of a load on a floor, because the load is spread out over a large area. Most floors are designed for a load minimum of 60 pounds per square foot.


Junkman, how can you say such a thing /forums/images/graemlins/confused.gif /forums/images/graemlins/blush.gif /forums/images/graemlins/grin.gif?
Most building codes specify a residential live load floor capacity of 40 psf. Some building codes will even reduce that to 30 & 35 psf for sleeping areas. Maybe the newer waterbeds have less volume of water than older waterbeds, but the weight should not be ignored.

My $.02 from your friendly professional structural engineer.

Yooper Dave

 

[boustany]

</font><font color="blue" class="small">( I may have missed it but I didn't see anything in your post indicating whether or not this structure was attached to your living quarters or not
)</font>

It was in the first thread/post:

</font><font color="blue" class="small">( "We're planning an addition to the house which will include a single car garage at living area level, and I'd like to utilize the potential space under this garage by extending the basement into this area also."
)</font>

 

[keeney]

I would go with the pre-cast concrete planks as the least hassle way of doing this.

Alternatively,
You could do a fairly thin top-coat of concrete over a wood structural frame and plywood deck. That would avoid the issues concerning plywood sagginess and burning tires on a wood floor and all. Use a rubber waterproofing membrane designed for this applicaiton like Bituthane on the wood deck under the concrete topcoat.

You could also do a cast-in-place structural concrete floor by adding enough steel and concrete thickness (engineering probably required to determine how thick, how much steel, and how much wood framing underneath). Once its cured, you could pull the wood frame and decking out and use them for the frame and decking of the non-garage part of the 1st floor over the basement.

 

[jtcweb]

I would go with the concrete planks. They are 4' wide and as long as you need them. I got a price quote of about $3500 delievered to S.E. MI for 24' x 24'.

 

[rambler]

Can you put an occupied room under a gragae in your location? Many building codes prevent this, and with good reason.

You can put the garage at the bottom & live above it. Salt, fluids, explosive vapors, overloaded vehicles tend to all go down, and I believe, if it is even allowed, you would greatly decrease the value of your house by putting in an upstairs garage.

I would not look twice at a house with a garage with a wooden floor over a living quarters - couldn't pay me to live in such a thing. Can not imagine such a thing would be legal anywhere, nor would it be wanted by anyone else. If you are allowed to do the upstairs garage, at least make it a concrete floor!

Just my thoughts.

--->Paul