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Deepening basement

[email protected] | Posted in Construction Techniques on October 30, 2002 05:56am

    I have a 100 year old balloon- framed house with a basement that is only about 6.5 feet high to the bottom of the first floor joists.  The floor is a rat slab which is only about 1/2 inch thick and breaking through in spots.  I would like to deepen the basement to have a 7.5-8 foot ceiling to gain living space.  The problem is that the top of the footing is at the level of the current floor.  The foundation consists of a cut stone footing about 6 inches thick, then a mortared sandstone foundation wall.  Only about 4 feet of the basement wall is below ground.   The foundation is sound with minimal settling.  The subsoil is heavy clay which stays moist most of the time.  There is no water seepage through the walls, but ground water often rises through the floor. 

I figure that I’ll have to build a stem wall inside the footing to prevent migration of the bearing soil, but I’m not sure how to hold it in place while doing the work.  Is this a practical idea, or should I give up on it? 

 

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  1. User avater
    jonblakemore | Oct 30, 2002 07:40pm | #1

    Do you have access? For instance, do you live on a hillside where you could open up a section of the wall for an entry for work?  If you can't get into the basement easily then it will be very, very expensive or an awful lot of work.

    Jon Blakemore
  2. Piffin | Oct 30, 2002 10:05pm | #2

    "but ground water often rises through the floor. "

    I think you've provided your own answer unless you are either trying to buoild a swimming pool or want to spend more on the basement than a new house might cost. Then it would depend on pumps, power not ever going out, and excellent concrete, waterproofing, and drain systems.

    .

    Excellence is its own reward!

  3. andybuildz | Oct 31, 2002 12:16am | #3

    Doc

         In my opinon..with a clay floor and water seepage as I had in my last house DONT DO IT! Youre only asking for trouble especially if your talking living space. There are methods but I dont think its cost effective in the long run. One thought is that your taxes wont really go up which I'm bettin' your thinking about depending on where your from but the steps your going to need to go through with water I'm betting will outweigh that and your nights sleep eventually will be effected. I'd say if you need space.....add on above ground and have a pleasant nights sleep.

    Be well

              Namaste

                           Andy

    It's not who's right, it's who's left ~ http://CLIFFORDRENOVATIONS.COM

  4. user-3146 | Oct 31, 2002 04:29am | #4

    Doc

    I have seen it done, and done it myself, First of all what is your original foundation made from?

    Jason

    1. [email protected] | Oct 31, 2002 03:24pm | #6

      The foundation is cut stone, about 8 inches thick above ground and appears to be about 12-16 inches thick below grade.  The joints are mortared.

      1. user-3146 | Nov 02, 2002 04:00am | #7

        Scrape out a little of the mortar, If it's crumbly to the touch its Lime mortar. It would be best to use the same type of stone. Buy or rent some 20 ton hydraulic jacks, make yourself some laminated 2x4 or 2x6 posts and a good sized beam so you can work in-between them. Pump up the jacks up just enough so you can tell that the beam is supporting the joists in case of a fall out. Break out the floor in the section your working on and start to dig. Only work on small sections at a time such as 4 5 feet of wall. Be carful, and start to build yourself a knee wall slightly thicker then the foundation stones (in your case 12 inch or 16 would probably do. Use the same type of mortar that was there. If it's lime a good mix is 2 parts lime 5 parts masonry sand (I usually put in a couple scoops of fine silica sand, because the mason sand we get around here dose not have much fine particles in it. If your sure its a concrete based mortar ask the best mason in town for advice on how best to set your new stones. As far a water problems go the old guys used lime, because it lets water in or out and concrete does not.

        jason

        1. Piffin | Nov 02, 2002 06:38am | #8

          Jason, You seem to be missing some critical information from his original description. Doc says that water occasionally comesup through the floor. That tells us that he is down to the water table now. There is an obvious reason why the original builders stopped where they did. If he is to dig down three feet, he will be working in three feet of water. He'll actaully have to go another foot or more to create space for footings, drain pipe and pumps. Then and only then, can he start to follow your advice for rebuilding the wall. I don't believe he can do it five feet at a time in those conditions on clay soils.

          Lime mortar is not a pemanent solution for below grade, especially not below water level. The advantage of lime based is that iot heals itself. The way it does this is that the lime will disolve into water passing through it and move to another location so a crack will eventually heal. But this is a disadvantage with steady water flow below grade. The lime will be entirely leached right our of the mortar until nothing is left but the sand. I've replaced foundations only a hundred years old for this very reason. That is why so many old rubble foundations are now plastered over. The portland surface coat is holding the limebased in place for another generation.

          Digging out this stacked cut limestone foundation would be a mistake, IMO..

          Excellence is its own reward!

          1. Handydan | Nov 02, 2002 11:12am | #9

            If headroom is the issue, which I think was the start of this idea, why don"t  some of yu who are smarter than I am, tell how to raise the house up a couple of feet, so we don't get any closer to that dreaded water.   I am not a good enough engineer to know if you can add to the existing foundation or new would be required, but I think the answer is easier up than down.  Just an idea.

            Dan

          2. [email protected] | Nov 02, 2002 03:49pm | #10

            I appreciate all the responses.  I did consider raising the house, but believe it or not the peak of the roof would then be higher than allowed in my town.  I also felt that in the long run the amount of work would be prohibitive even if I could get a variance.

            I did have one waterproofing contractor out who recommended a "Wisconsin wall".  The way I understand, they would dig a trench along the inside of the foundation footing about 2 feet down without (hopefully) undermining the bearing soil.  They would then pour a concrete retaining wall (wider at the base then at the top) whose top would be a little higher than the footing.  This way, the existing foundation footing would still be resting on the existing bearing soil, the concrete would just be there to prevent that soil from migrating in and undermining the footing.  They would then put an interior perimeter drain in which would lead to the existing sump pump.

            After reading all the responses I am a little more nervous about the project, but I am not totally convinced it is not possible.  We really like the house, but need a little more room.  The purpose of the space will be on the line of a rec room, sewing room, and storage.  The lot we are on is relatively small, and adding on would remove too much of the backyard.  I realize that the basement will be a fair chunk of money, but if we ended up with an extra 800-1000 sq. ft. of usable space, the cost per square foot should still be less than adding on.

            Further comments?

          3. Piffin | Nov 02, 2002 04:07pm | #11

            I too considered raising it up which would normally be cheaper than digging down into water table. You'd have to go a long ways to convince me that you can go down cheaper than an addition and I've done lots of both..

            Excellence is its own reward!

          4. junkhound | Nov 02, 2002 04:35pm | #13

            Yeah Piffin, but think of all the exercise you get carrying buckets of dirt <G>.

             Beats jogging anyway IMHO.

          5. Piffin | Nov 02, 2002 07:29pm | #14

            Whaddyamean carry?

            I just eat it!

            LOL.

            Excellence is its own reward!

          6. junkhound | Nov 02, 2002 04:34pm | #12

            Never heard it described as "Wisconsin wall", it was always the "embankment" back in IL.

            Sounds like maybe your zoning won't allow an addition.

            If you do dig out and do the 'embankment', dig out enough for 4" pea gravel and a 4 ft square grid of drain pipe inder the floor.  You are essentially trying to keep a shallow dug well pumped dry. Did similar on son's house a few years back in Seattle area, Dad did it to his 1910's house (brick foundation and footing) in IL in 50's (no problems since**).  Pop paid kids in boy scout troop in candy and hamburgers and 25 cents/hr to carry dirt out in coal buckets up the cellar stairs.  

            ** caveat - you need to be sure you have a double sump pump arrangement and generator to deal with power outages, pump failures, and occasional heavy rainfalls. My parents dealt with this type problem by having asphalt tile in the basement, anything that could be water damaged on 4" pedestals off the floor - sometimes even 2 pumps could not keep up with 6" rain an hour.

          7. andybuildz | Nov 03, 2002 06:19pm | #15

            Doc

                I had once built an addition that was two feet higher then the allowed code around here. I built a retaining wall around the addition two feet high and added soil and plants and it passed code. Look into that idea.

            Be well

                   Namaste'

                                andyIt's not who's right, it's who's left ~ http://CLIFFORDRENOVATIONS.COM

  5. rez | Oct 31, 2002 05:47am | #5

    It depends on the definition of living space and what you plan on using it for. I have the same configuration you described except old double poured concrete walls and a sandy soil with a water level about three feet beneath the floor.

    That's a lot of work and money for your extra head space and it will end up having some type of moisture problems if fabric or paper is being involved down there. I just dug down to the middle of the footing, 6mil then poured and just treat it as work space/utility with lower headroom.

     

     Let the thunder crack and the waves roar.

     We're going on.

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