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  1. #1
    Join Date
    Jan 2012
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    Default Crawl space excavation

    I currently own a 1925 side hall colonial in staten island, new York. In the 1980's and extension was added to the back of the home. It's a two story structure with a crawl space beneath it. In an attempt to gain more living space, my wife and I are considering having the crawl space excavated, thereby extending the original basement. Our questions are:

    What is the best way to do this? We have been told that removing the wall that faces the driveway may be best. By doing this we could get some heavy machinery in there. However I am certain this would be the most costly method. Any suggestions?

    Whichever way we do it, our main concern is that the job is done right. The last thing we want are structural problems.

    This project would also include breaking through the existing cinder block back wall of the basement. The crawl space has a concrete slab base. The joists for the flooring are about 2 to 2 1/2 feet above the slab.

    Thank you!

  2. #2
    Join Date
    Jul 2010
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    Default Re: Crawl space excavation

    I read your posting twice, and I recommend you talk to an engineer.

  3. #3
    Join Date
    Aug 2008
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    Default Re: Crawl space excavation

    I would agree with dj; I had this done some years ago on perhaps a simpler foundation excavation than you describe, and believe me, it can get very involved, complicated and expensive.

    Be prepared to deal with the following items, although there will no doubt be some variations:

    This type of project is clearly not a DIY venture in any stretch of the imagination; be aware that the town building permit officials (be polite to them, they have lots of power) are unusually strict and very picky when it comes to anything involving the foundation/structure modification of a building, which they see as a potential SAFETY THREAT to present & future occupants of the building; you might get the distinct impression that they think the building belongs to THEM, the way some of them act.

    Before they will issue you a building permit, which must be displayed at the work site, they almost always insist that you hire a civil engineer (approx $1k to $2k) to draw up a plan with diagrams of all slabs, walls, & methods of supporting/shoring up with temporary timbers, etc. while construction takes place.

    You will also have to hire a contractor (see Yellow Pages: "Excavation Contractors","Contractors,General") who agrees to take on the job & do it to the engineer's specifications, and submits his estimate; it's best to get several estimates; each contractor will have perhaps slightly different ways of doing the project, and estimates can vary considerably.

    The town will issue you or the contractor a permit if the above two steps are completed satisfactorily; the town inspector & the engineer are required to periodically visit the site to make sure everything's OK during construction, & everything complies with town building codes.

    Then, finally, there's the cost, which could well be into the tens of thousands of $$$$.

    It's best if you can get several contractor estimates & finally settle on the one that best meets your expectations as to price & method of work, and then let the contractor carry the ball to deal with the engineer, the people at town hall, Permits, etc.
    Last edited by dodsworth; 01-16-2012 at 11:02 PM.

  4. #4
    Join Date
    Aug 2007
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    Default Re: Crawl space excavation

    Ditto to the two previous posts --- dodsworth summed it up pretty well.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  5. #5
    Join Date
    Jan 2012
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    Default Re: Crawl space excavation

    I should clarify - I am not attempting to DIY this. I can do many things around the house. There's a few things I do not venture into, electric being one of them and foundations another. I am just trying to get some insight from anyone who has had experience with such projects.

    We had our main bath renovated two years ago and we were not completely pleased with the overall result. If I am going to have a project of this scope done, I need to make sure the contractor is reliable and knowledgable. I figured if I go into the project with some idea of what needs to happen, that could be to our advantage.

    The major issue with this project, other than the tearing down of walls and excavating , is that we currently get water in the crawl space after heavy rains. It appears to me that there is not enough of a runoff. After inches and inches of rain. When the water level rises in the back yard, it eventually seeps into the crawl space. I imagine this will require regrading of the backyard?

    Would anyone have an idea of the cost of this type sod project? Are we talking 50k, 60k?

  6. #6
    Join Date
    Jan 2012
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    Default Re: Crawl space excavation

    Ignore sod, that's a typo.

  7. #7
    Join Date
    Aug 2007
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    Default Re: Crawl space excavation

    It's hard to say because many variables -- size , type of soil conditions , local labour and material costs , site conditions , etc.
    Consider it will be more expensive because there is a building in the way which needs to be supported compared to digging and pouring a basement on a vacant lot.

    You're probably looking at $30k minimum -- depending on the variables.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  8. #8
    Join Date
    Dec 2007
    Location
    Tennessee
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    1,381

    Default Re: Crawl space excavation

    When it comes to adding space, it is a lot cheaper to go up rather than down. How much space do you have in your attic? If the attic doesn't have enough headroom, is it feasible to put on a steeper pitched roof to get the headroom?

  9. #9
    Join Date
    Aug 2007
    Location
    Maryland
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    Default Re: Crawl space excavation

    I pretty much agree with what's been said. Underpinning and extending a foundation is going to be very costly and all you end up with is more basement. I realize that would be nice to have, but at what cost.
    The work is somewhat specialized and an engineer is required. Excavation on both sides of the wall is required and it will need to be done in sections. I've underpinned foundations to provide additional support for a second story, but never to add a full basement under ground. Not saying it can't be done, but it's not often done in my experience.
    Regrading is likely to solve the water problem and adding a foundation drain and waterproofing might be needed if groundwater is a problem.

  10. #10
    Join Date
    Jan 2012
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    4

    Default Re: Crawl space excavation

    We have a full attic. In fact when the addition was added to the rear of the home - they also extended the attic. I'd estimate that it is about 40 feet in length, at least. In its current state, the ceilings are entirely too low. I'm only 5'5 and I have to watch my head in some areas.

    The only access to the attic is via a ladder, so a new staircase would be required. Also, I imagine it would be difficult to cool the attic. We have AC units on the first and second floors, no central air.

    Would doing a roof raise with a new stair case and cooling system be less costly than expanding the basement?

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