footing/foundation walls in attached garage


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Old 05-11-07, 08:15 PM
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footing/foundation walls in attached garage

My contractor deserted me so I am on my own now so bear with me. Part of project is attached garage. I was going to rent machinery to dig for footing myself. Can the concrete sub simply poor into the trench I dig or will they have to put up wood forms the way they did for my basement? I will use my laser level to assure it is excavated to correct depth everywhere. I live in MD and plans call for footing to be 30" below grade. Does a garage need any sort of drain tile? The plans show it but I can't see why it is needed. I already had a poolhouse with plumbing in the location so I plan to put a drain in the center of the garage using the existing plumbing (assuming allowed by code). If it needs drain tile, then they probably have to put forms up otherwise I wouldn't be left with any room to put it as concrete would fill trench completely.

The property slopes and the one side will need to be filled a lot (on the inside). Can I put the dirt I have around from other excavation, compacting it as I go and then let it sit for a while and then throw in 4" stone on top and compact that and then pour slab? Or does the fill have to be all stone?

Thanks
 
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Old 05-11-07, 08:17 PM
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If building a garage, local building codes will dictate what needs to be done. Changes to structure require a building permit. Contact your local building code office.
 
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Old 05-11-07, 08:30 PM
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Of course I have to follow codes but I was wondering if drain tile is often/always/never required for a garage-just from peoples experience. I have to make addendum to the building permit and put my name on it anyway so I can simply eliminate drain tile on drawings if it isn't needed.
 
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Old 05-13-07, 10:17 PM
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Back in Chicago we only put drain tile around the basement area, never the garage even if it was attached.

Some villages will let one pour a trench foundation for an attached garage and some will not, you need to talk to the village inspector for that one. If you go with a trench be sure to flare the trench at the bottom or it will not pass inspection. The flare needs to be twice as wide as your wall, for instance… 8” wall = 16” flare to act as a footing.

I would not use the dirt from the trench as a sub base even if you compact it, compact your stone base in 6” lifts.

Be sure to remove all vegetation (grass) from the inside where your floor will rest before adding your stone base or this will rot and eventually your stone base will drop leaving a gap between it and your slab.

If you cannot pour a trench foundation you can rent the forms for your project, call your local concrete supply company and ask about it.
 
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Old 05-14-07, 04:30 AM
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would the base have to be flared or could the trench just be 16" wide (using your example)

the low side is 4' 6" lower so would require that much fill. So if I understand you, I should fill all of that with stone, NOT dirt and then top off last foot or so with stone.

Thanks
Bill
 
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Old 05-14-07, 12:05 PM
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would the base have to be flared or could the trench just be 16" wide (using your example)
You are missing the point here, the reason for a footing is to support the wall and there are rules for this. An 8” wall needs a footing that is 16” wide and 8” deep, a 10” wall needs a footing that is 20” wide and 10” deep. For a flared footing in a 8” trench foundation one needs to flare the trench 4” on each side but because you are flaring as apposed to pouring separate you actually have to start your flare about 10”-12” above the bottom to achieve an 8” depth at the 4” wide point.

Most villages insist your gravel base rest on virgin, undisturbed soil, so YES it will take that much fill. A few years back I poured a pole barn with a radiant heat floor, the back wall was three foot below grade… we used forty ton of stone to bring it up to grade.

You might try to call your local ready mix company and see if they sell something called “washout”. It is the remains of the left over concrete that is diluted and washed out of the ready mix trucks at the end of the day. It compacts well and is usually accepted by most villages as a good base… and it is cheep, sometimes free if you have a truck to haul it away. Than all you need to do is cover the washout with 4” of stone.
 
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Old 05-14-07, 01:13 PM
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footing/foundation walls in attached garage

The 2006 IRC says for a lightweight one or two story structure, the minimum width is 12". Any spread footing projection beyond the foundation wall must be at least 2", but not more than the footing thickness. The minimum footing (if required) thickness is 6". This even applies to the poorer natural soils.

Some areas with a tradition of heavy walls and multi-story residences may lump everything together and request more for all uses to avoid mistakes.

With decent soil, you really do not need the traditional wide footings for most construction. Some cities do not keep up to date.

Check with your municipality and find out if they require formed footings or if you can skip the footing and just use a thicker concrete foundation wall. Then find out if the width requirement is the old code, new code or the local modification.

You will still have to connect your attached garage foundation to you home foundation.

Do not use the "dirt" you have around for any fill except under the black dirt in your flower garden.

Dick
 
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Old 05-14-07, 01:29 PM
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I guess I am missing something. in your example, an 8" wall needs footer 16" wide. So if I make trench 16" wide and pour into it, it will be 16" wide? I know that I have to have it 30" below grade so I would dig the "low side to 30+ " and on the "high" side I will have to dig down 4' 6" just to get to the top of the footer on low side. Then I dig down extra 8" which is required thickness of footer on the high side. so when I pour it, it is all min 30" below grade, all min deepness of 8", and would be min 16" wide-the width of the trench. Then I put 8" wall on top of it. So I don't understand why I would have to flare it? The footer for my addition was not flared. Was done like above but they used wood forms on the top. The walls appeared to be perpendicular. The were dug with back hoe and I don't recall the workers getting inside and flaring them.

I think I see what you mean now. I was going to pour separately! Have footer poured first and then have the metal forms put up to pour the walls, which will be rebar reinforced. Your way may be better cause they would only have to come once, but How could you do it in single pour if the walls need rebar?

Sorry, like I said, bear with me cause I am just trying to understand this stuff and my contractor left me in terrible mess-both with my addition and with my finances so I have to try to do whatever I can.

where can I find out info on local codes? Do counties usually have a book I could get? Or something online? I will check their website. I know I got info for my variance there but I don't remember this sort of info on their web site. I hate to have to run to ask them everytime I have question?

thanks
Bill
 
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Old 05-14-07, 02:05 PM
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footing/foundation walls in attached garage

Go to your local code office (township, city or county) and talk to them face-to-face. Explain that your contractor deserted you and yo want to finish things right, but keep the cost within reason since you are forced to do it yourself. - It sure beats a telephone call and they may lead you through everything since they don't want to spend a lot of time with later details and extra trips.

Dick
 
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Old 05-16-07, 10:56 PM
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A concrete footing and a concrete wall are two different entities that make up the foundation, locked together with a keyway in the footing. This type of foundation is poured in two separate phases… first the footing than the wall is framed and poured.

When I say trench foundation one uses a trenching machine equal to the width of the wall 8” for wood frame and 10” for brick veneer. It is the bottom of the trench that is flared to the footing specifications to create a widened bottom for support and can be poured all at once with less digging and no backfilling. As I mention some villages no longer accept a trench foundation when attaching to an existing house.

The dimensions I gave you are the code for the entire Chicago land area, not only did I never see anything different from any of the blueprints I worked from, I also studied architectural drafting and have drawn up plans that have passed the codes and have been build from.

The reason one cannot just pour a trench without a flared bottom is without proper soil tests there is no way to tell what the ground is like four feet below. If poured over an area of bad soil that trenched wall can sink pulling the added structure away from the house, sometimes pulling part of the house with it. I just fixed one like that here in Southern Illinois.

Here is a simple test for you, take four evenly length 2”X 4” about three foot long, turn them on edge and make a square box, place the box in some sand and stand on it, than rock back and forth some. The box you just made will sink into the sand and start to come apart. NOW attach 2”x 4” to the bottom of your box laying flat… this will act as a footing. Now place it in the sand and stand on it and rock. It will not sink or come apart
 
 

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