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Thread: Digging a basement deeper?

  1. #1
    DIY Senior Member Nate R's Avatar
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    Default Digging a basement deeper?

    I've heard of people digging basements deeper. Say you have a 5 ft crawlspace, and you want to dig it out to 8 feet to make it liveable space.
    I've done some research on it. Seems one way is to raise the house instead. Digging straight down will often require new footings since you'd be under the old ones.

    But what about doing it like the pictures below? You don't disturb the existing footing, and you still gain the headroom throughout much of the room.




    I've been in one house where there was no basement, and someone hand hand dug one in dirt in the middle of the house similar to above.

    Any thoughts on what would be wrong/difficult in doing it like the pictures above? (Other than the difficulty of dirt transport?)

  2. #2
    Plumber Cass's Avatar
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    Any dirt can be dug out and removed as long as the removal won't affect any footers and or foundations now or in the future. Foundations rely on earth pressure outside the foundation to help hold it up.

    During droughts watering the earth around your house is very important so as not to allow the earth to dry out and pull away from the foundation causing problems.

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    Jack of all trades frenchie's Avatar
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    I've seen them, too, but I'm not sure how you could maintain bearing, under the footings, excavating like that. The norm, when digging around the outside, for adding drainage & etc is to leave at least a 45* slope, under the footing... not straight down like that... I would definitely lift the house, instead.

    Neither option is something I would undertake myself, this is a job for a foundation specialist or a structural mover, who's done it before and knows which engineer to consult & etc.
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    DIY Member chel_in_IL's Avatar
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    Quite a few houses near where I live have had their crawlspaces dug out. Many of the homes were built without basements to keep the cost low, not because they were built on a swamp. The basement looked exactly like your pictures, with the "shelf" around the outside.

    Never heard of any later issues with structural damage... houses are 40-50 years old and still standing...

    Michelle in Northern IL

  5. #5
    Jack of all trades frenchie's Avatar
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    I've seen it a few times, too.

    The reason I say don't DIY it, isn't possible long-term weakening.

    It's the risk of collapse while doing the work.
    Master Plumber Mark:

    there is nothing better than the
    manly smell of WD 40 in the air
    while banging away on brass with a chisel and hammer...

    it smells like......victory......

    do not hit your thumb...
    __________________
    Just so everyone's clear: I'm the POODLE in the picture ("french", get it?) The hot woman is my wife.

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    DIY Senior Member Nate R's Avatar
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    Thanks all! I appreciate the advice. The house i live in now isn't quite slab on grade. It's built over a "crawlspace" a few inches deep.

    We'd talked about digging out a basement for a while, but decided the added value wasn't worth it in this house. The water heater and furnace are already boxed in on the first floor, and the space gained wouldn't be worth doing it. But, we've looked at houses w/ 5 ft basements, and other houses with no basements. I'll keep this in mind that it may be possible when we look for our next house. I would definitely consult an engineer first.

    In our current house, we're going to be replacing the detached 20X20 garage with 24X20 garage, so we'll get trusses for a room in the attic instead of building a basement. Much cheaper and not much less space for storage than a basement would add in our house. The main foundation is about 20X20, so I think we'd only get about a 16X16 basement. Garage room will be 12X20.

    The real challenge will be if I ever have to replace the water main or sewer line, which go through the floor in the house into the ground. I think then I'd dig down the 6 feet or whatever, and pour small footers and build a concrete wall forming a "room" about 4X4'
    Last edited by Nate R; 12-05-2007 at 11:08 AM.

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    Jack of all trades frenchie's Avatar
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    FWIW, I recently priced lifting a house, and it costs a lot less than I expected. It wasn't cheap, by any means, but still: much less than I expected.
    Master Plumber Mark:

    there is nothing better than the
    manly smell of WD 40 in the air
    while banging away on brass with a chisel and hammer...

    it smells like......victory......

    do not hit your thumb...
    __________________
    Just so everyone's clear: I'm the POODLE in the picture ("french", get it?) The hot woman is my wife.

  8. #8
    General Contractor Carpenter toolaholic's Avatar
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    We have done this ,I'm a licensed G. Contr. You need an Eng. This is not a do it Yourself project! One guy saw His house crumble!

  9. #9

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    Quote Originally Posted by Nate R View Post
    I've heard of people digging basements deeper. Say you have a 5 ft crawlspace, and you want to dig it out to 8 feet to make it liveable space.
    I've done some research on it. Seems one way is to raise the house instead. Digging straight down will often require new footings since you'd be under the old ones.

    But what about doing it like the pictures below? You don't disturb the existing footing, and you still gain the headroom throughout much of the room.




    I've been in one house where there was no basement, and someone hand hand dug one in dirt in the middle of the house similar to above.

    Any thoughts on what would be wrong/difficult in doing it like the pictures above? (Other than the difficulty of dirt transport?)
    There are many things to think about before building a basement. One of the most important thing is the cost to build it.
    Installing a Drain Tile to the foundation of your basement should not be forgotten. The Drain Tile will keep you r basement dry by diverting ground water away from it. Other things to consider when building a basement are labor costs, equipment rentals, finishing and of course your building permit.

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