Crawlspace conversion to Basement

Old 03-01-14, 07:51 PM
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Crawlspace conversion to Basement

Hey all. First post here.

I am considering purchasing a house pretty soon if it's cheap enough. The idea would be to eventually dig out the crawlspace and create a basement after doing a remodel to the main floor. This would allow me to fit a staircase in along with a more space efficient floor plan.

Let me say that I know how crazy it is to do this, a lot of work, and danger due to load bearing dirt. I would have to consult with an engineer at some point to follow through with the process. I'd be doing everything DIY aside from perhaps some beam installation if that would need done (depending on the crawlspace currently.)

Few questions to stay brief. Has anyone here done this, that can provide some insight? I'm looking for tips, useful information, and general advice...I'd like to stay away from comments like 'Don't do it' - heh...I'm a bit hard headed on the idea.

How much of this can be DIY? I would be doing this on my free time and not all day long - so I'm not worried about tiring myself out. I'm sure it will help build my body up, but possibly kill my back sooner. I would plan on doing most digging by hand with some help of a conveyor system after things are moving along.

What is the most cost effective way to install the walls? I have read up on underpinning, doing saw tooth designs, or staying 45 degrees from the initial footing - which would make this project pointless. I believe I would like to do either an A B C wall where I go in sections, let the concrete cure, excavate beside that and do a second section, then the last one after that cures. If not this, then I would do a wall say 2' inside from the footing with underpinning to start it.
Old 03-02-14, 04:25 AM
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Welcome to the forums!

Back in the late 50's my grandfather excavated under his old farm house. He had a cellar but it only had about 4' height. He hand dug the entire thing! He erected a 4' block wall inside of the stone foundation and poured a concrete floor. He poured a concrete shelf above the block wall up to the stone, made a nice clean area for storage. He did this work after he 'retired' although he was still actively farming 27 acres, it took him several yrs to complete the job. While I doubt he had any advice from an engineer [or permits] you need to get both!
Old 03-02-14, 04:53 AM
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First is the "don't do it". Least expensive and possibly best is to simply buy a house that already has a basement. Buying a house and then digging the basement is sorta like shopping for a used car with the intention of replacing the engine. It can be done but is it worthwhile???

One method is to dig down to the footer then go outward and down at a 45 degree angle until you get the depth you need. Then build a wall and back fill. You end up with a reduced size basement but digging well away from the footer is minimally disruptive to the foundation and is somewhat DIY friendly. Since the house stays in place most of the work needs to be done manually so it will be slow, hard work.

To do a really proper basement you can hire a house moving company to jack the house. They install steel beam under the house, raise it and support it on temporary cribbing. With the house up and off the foundation equipment can be used to excavate under the home, pour new footers, build new foundation walls, pour a basement floor then set the house back on the foundation. Even though it sounds extreme house movers are surprisingly inexpensive for the work they do and being able to use equipment will certainly speed the process and may even lower the cost.
Old 03-03-14, 01:02 AM
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More than fifty years ago I had two neighbors that excavated their crawlspaces into finished basements. My family also did a partial excavation and all three houses continued to stand for another twenty or more years until demolished for the construction of apartment houses. This was in Seattle and there were several earthquakes during the years after the digging with NO problems. None of the people who did this ever had a consulting engineer and I'm not sure any of them ever even had a building permit.

I am NOT trying to negate the good answers already given but I AM trying to point out that lots and lots of people have accomplished what you want to do quite successfully. Don't give up because of a few naysayers.
Old 03-03-14, 05:57 AM
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I have seen this successfully done, typically in a manner similar to what Mark described, and in fact was very close to doing it to my own home maybe 15-20 years ago, but decided to add out rather than down. (My grandfather did this to his large farm house in the 30's, and, once the initial hand digging was done, my mother was the one charged with backing the team under the house, and leading them out with the scoop attached.) But I have also seen it started and abandoned, whether due to soil conditions or lack of effort, which it would definitely take a lot of. So it's very possible, but the amount of floor space to be gained, soil conditions, amount of free labor, and other conditions are obvious factors. 45 degrees is an arbitrary figure; you are looking for the angle of repose, which is going to vary with soil conditions, and which an engineer can provide to you. Then, of course, that angle needs to be adequate during the course of the entire project, which is going to take a while, and will most likely span seasons, so you may have varying levels of ground water and other such changes to allow for. Doable, but will take some thought adn expertise.
Old 03-03-14, 08:37 AM
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First, most basements are a pain, my personal opinion, so going through a long, hard, and with some expense process to end up with a less than fully useful space doesn't make a lot of sense. There are plenty of threads here on the problems related to basements.

Projects that start and are completed in a short time can avoid weather issues, rain, frost, being the major ones. I'll let you judge if digging a hole in your basement is going to end up (during construction) being a pond. 98% of all basements out there and 100% of all crawlspaces were never properly waterproofed or moisture proofed from the start. Two or three layers of tar does not eliminate those problems. Treatment should have continued down under the footings and up and continuously under the slab. Not sure how you are going to do that.

I read a couple of comments that years ago similar work was done without permits. Although that may have worked years ago, today they require full disclosure at time of sale and they check for permits issued. Local codes vary so check and follow the rules. Remember, the work you will be doing inside will be obvious to everyone outside and questions will arise. Some are now using Google overhead views to spot work in progress or changes.

There is also the issue of insurance. Work without proper engineering will/may NOT be covered by your insurance or related claims. Best to ask in advance.

Note, I didn't say to not do this, but there are other ways to spend that much time and money to end up with more useful space.

Old 03-04-14, 03:04 PM
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Can you do this? Sure

Would I do it? Probably not; just too much work and I would look for a different house instead.

My house is like this - the builder built the same one on the next street but excavated for another basement level where I have crawl space. Would love to have that but I'm not going to bother; I'll move to another house.

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