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  #1  
Old 01/31/09, 10:28 AM
 
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under gound room under garage

Any ideas on how to dig out under garage slab support it and still park 2 cars in it after it's finished?

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  #2  
Old 01/31/09, 10:37 AM
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most safe rooms on single floor dwellings are dug under the front porch during construction .

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Old 01/31/09, 11:00 AM
 
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Unless you know how thick the concrete is, what the concrete mixture is, whether it has rebar in it and if so how much and how it's laid out... there is no way to determine if it is even possible... much less whether it is safe or not.

Assuming all the above factors were in the safe limits, you would still need structural support... either very heavy timbers or structural steel.

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Old 01/31/09, 12:14 PM
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I recall seeing or reading of a company which specializes in putting in storm shelters in existing garage floors. Likely they cut a large hole, dig, drop in their unit, backfill and perhaps do some concrete finishing work.

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Old 01/31/09, 02:27 PM
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That's, not a good idea unless you're willing to do a lot of work and spend a lot of money on structural support. Most concrete floors are 4 to 6 inches thick with very little or no steel reinforcement. Concrete has a high compressive strength (as a car sitting on it id OK) but a low tensile strength. That is if you dig out under the concrete it must be reinforced supported with material that can with stand high tensile forces (like steel beams) or it will pull apart and fall in under low loads. Please consult with a structural engineer before attempting this. All of the posts above contain good advice. Good luck.

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Old 01/31/09, 03:09 PM
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Quote:
Originally Posted by Ken Scharabok View Post
I recall seeing or reading of a company which specializes in putting in storm shelters in existing garage floors. Likely they cut a large hole, dig, drop in their unit, backfill and perhaps do some concrete finishing work.
I have seen this company as well. The unit is thin, so that a car can straddle it, without having any of the car's weight bearing on the unit. It is also designed so you can open the hatch and get in while the car is parked over top of the unit. very slick.
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Old 01/31/09, 05:43 PM
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There's no practical way to do that. I've seen some arrangements like that, that were built before the garage was built but some of them had water problems. If you're bound and determined, jackhammer the floor and remove it and excavate the room. Pour a floor slab with a drain as well as install a perimeter drain running to daylight. I'd embed rebar in the slab that extends vertically into the cells of the block. Once the walls are as high as the rooms ceiling grout the cells and set plates with Nelson studs for metal joists. After the joists are welded to the bearing plates, continue the block course up to within the thickness of the slab from the surface. Backfill the exterior faces of the block walls with sand after waterproofing the block on the outside. Use Q-deck placed over the joists to serve as the support of the concrete slab that will be the new garage floor. Tie the vertical rebar into the rebar placed on chairs on the Q-deck. Place concrete for the new garage floor.

You should find a small engineering company to do the actual design. That shouldn't cost much.

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  #8  
Old 01/31/09, 09:53 PM
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Barrel vault.
l

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  #9  
Old 02/01/09, 12:28 PM
 
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Originally Posted by Darren View Post
There's no practical way to do that. I've seen some arrangements like that, that were built before the garage was built but some of them had water problems. If you're bound and determined, jackhammer the floor and remove it and excavate the room. Pour a floor slab with a drain as well as install a perimeter drain running to daylight. I'd embed rebar in the slab that extends vertically into the cells of the block. Once the walls are as high as the rooms ceiling grout the cells and set plates with Nelson studs for metal joists. After the joists are welded to the bearing plates, continue the block course up to within the thickness of the slab from the surface. Backfill the exterior faces of the block walls with sand after waterproofing the block on the outside. Use Q-deck placed over the joists to serve as the support of the concrete slab that will be the new garage floor. Tie the vertical rebar into the rebar placed on chairs on the Q-deck. Place concrete for the new garage floor.

You should find a small engineering company to do the actual design. That shouldn't cost much.

I've back filled with sand in the past and when it gets wet tends to settle too excessivly and causes bowing in a block wall. But I was thinking of of something along these lines. I'll just do my back fill with 1/4" gravel.

Another consideration is the amount of concrete needed will all most require a concrete truck, any ways of mixing large amounts of concrete not with a portable mixerhis isn't something I want the truck driver to know about.... Maybe the best idea maybe to just rent mulitple mixers at one time.
I'm going to have the engineering drawings made up by an out of state firm.
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Old 02/01/09, 12:30 PM
 
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Originally Posted by IBD View Post
That's, not a good idea unless you're willing to do a lot of work and spend a lot of money on structural support. Most concrete floors are 4 to 6 inches thick with very little or no steel reinforcement. Concrete has a high compressive strength (as a car sitting on it id OK) but a low tensile strength. That is if you dig out under the concrete it must be reinforced supported with material that can with stand high tensile forces (like steel beams) or it will pull apart and fall in under low loads. Please consult with a structural engineer before attempting this. All of the posts above contain good advice. Good luck.
Money isn't an issue, more of an issue is integrety, but the engineering firm should take care of that.
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Old 02/01/09, 12:31 PM
 
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Barrel vault.
l
Ok you're going to have to elaborate...that sounds fun
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Old 02/01/09, 01:40 PM
 
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Money isn't an issue, more of an issue is integrety, but the engineering firm should take care of that.
Anything can be accomplished when money is not an issue.
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  #13  
Old 02/01/09, 01:51 PM
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Talk to somebody with experience building freestall or hog barns. Should be pretty easy to use some of the prefab panels used in slatted floor barns to do the same thing (some of them are solid surface panels designed for driving tractors and feed wagons over).

If you had the sizing right, you could probably cut through the existing floor, build the room a bit smaller than the hole, and slide 1 or two panels in above the room for the new garage floor.

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  #14  
Old 02/01/09, 02:49 PM
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My neighbor had a room built under his garage when the house was built. There's some serious steel in there. As a retrofit I wouldn't think it was very practical.

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  #15  
Old 02/01/09, 03:18 PM
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One can do it with lots of steel but that is not necessary and may actually be a bad idea because salt brought into the garage above by the automobiles from the road will penetrate the concrete of the garage floor and corrode the steel. Embedded steel will then swell causing spauling and failure of the concrete.

If you are going to go that way it is important to protect the steel. Epoxy coated rebar is available which will offer more longevity than plain steel. This is now widely used in bridges here in the north country and probably along the coast lines where salt is an issue. It is also used in the construction of marine aquariums for this reason.

Another option is to design the structure to be inherently strong. Arches, domes, barrel vaults, etc. These require much less material, can be done with little to no steel and be stronger and more long lasting.

I have built a number of structures this way with domes and barrel vaults. They are strong enough to be buried and to park my tractor on (9,000 lbs) with the bucket full of gravel (1/2 cu-yd). Currently one of these barrel vault animal shelters supports two 1,025 gallon whey tanks plus the stone based platform I made to set the tanks on. The fluid in the tanks is around 16,000 lbs, add to that the stone base, the wood base above that, the tanks themselves and the winter snow load.

Our http://www.google.com/search?&q=site%3Asugarmtnfarm.com+tiny+cottage+barrel+vault+roof is also designed this way although I have not yet buried the roof of that. However it is strong enough and I will someday to give the cottage more protection from the cold winter air.

What ever you do, I would suggest understanding the engineering, or getting someone involved who does this sort of thing. It is not a simple hole in the ground which you are proposing. I can work but don't bet your life on it unless you know what you're doing!

Cheers

-Walter
Sugar Mountain Farm
in the mountains of Vermont
http://SugarMtnFarm.com/blog/
http://HollyGraphicArt.com/
http://NoNAIS.org

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  #16  
Old 02/02/09, 02:52 AM
 
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If money is no object, then you will find a way. The original floor likely will _not_ work.

Another issue- I assume you will want to be in this hole at some times, tho this is sounding like a project that I don't want to know the reasons for it - is fumes.

Many fumes from gasoline, exhaust, and other things stored in a garage settle to the floor, and will seep into your hole in the ground. This might not be a very healthy place - and could even be quite deadly on the wrong day? Think this through.

--->Paul

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