Leveling a foundation at the sills?

Discussion in 'Framing and Foundation' started by oldhome, Jun 9, 2011.

  1. Jun 9, 2011 #1

    oldhome

    oldhome

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    I have a 140 year old house with a mortared stone foundation - some walls are stone right up to the sills and some are stone below grade and brick above grade. One side of the house has settled 4" over the last century - we suspect undermining from roof runoff. (We plan to improve drainage this year.)

    Setting aside the concerns about DIY house jacking for now...

    Is it possible to level a foundation by jacking the low sides to just above level, and using lumber and/or mortar to fill the tapered void that my jacking created below the sills. I'm guessing that with a house this old, there is nothing other than the old mortar holding the sills onto the foundation. If that's the case, it doesn't seem that my "shimming" would make things any worse.

    I don't think I want to bring the house up more than 2" - that seems like enough trauma to do to the house, even if I go slow - I don't feel like refitting any windows.
     
  2. Jun 9, 2011 #2

    inspectorD

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    Well, settling of a home by 4 inches is usually a combination of some stone settlement, and the wood rotting. I would check att my sills with a good heavy probe from inside and outside first. Replacing the sills is a different job than jacking the house.
    140 years old and the home is not post and beam?
    And the wood also gets what we call "creep". (not to be confused with some of the characters here) It tends to stay the way it has settled sometimes, so jacking it up can make certain areas worse.
    Pictures are always fun for us to see also.
    Welcome.:)
     
  3. Jun 9, 2011 #3

    oldhome

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    Thanks, InspectorD.

    The sills are sound and 6" tall all the way around the foundation - they are 2' above grade, and give a good "knock" when struck. I have verified the height of the foundation with a laser level and confirmed that it is stone settlement of one kind or another. The worst side of the house is in the corner of an "L" that gets runoff from both the original gabled roof and the hip roof addition...

    Much of the original house is post & beam, though the addition shows hints of balloon framing: walls open to the basement.

    I can see how old settled wood might resist adjustment. I'm thinking of only correcting the 4" drop 1/2 way to a 2" drop (why push my luck?), and doing so over 3 weeks or so. Do you think that will help?
     
  4. Jun 9, 2011 #4

    inspectorD

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    Yes, you need to go slow with it as you already know, but over days not weeks. Keeps the cracks in the walls to a minimum. :)
    There is no way to get them perfect, and they do always need maintinence, but old walls are really neat. I would also put in a dehumidifier for the summer months if you do not already have one.
    Good luck with getting the jacks in place...and be careful.;)
     
  5. Jun 10, 2011 #5

    nealtw

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    We raised one last year from 3 1/2 to within 5/8. It's a scary job. It will only move about 1/4 at a time. Sometime we had to waite 2 or 3 days before it would move again. We didn't use big jacks as to not break anything.
    We figured the weight to be 100 lbs per sq. ft for each floor and the roof. More for the kitchen and furniture and more if the roof has more than one layer. After breaking the basement floor we figured a way to put all the weight back on the foundation while lifting.
     
  6. Jun 10, 2011 #6

    oldhome

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    Yes, slow will be the operative word.

    Do you think my idea about building up the sills with mortar and (in the higher spots) lumber? There will be some spots where the gap below the sills will be as much as 2" and other places that may taper off to nothing. Considering that my goal is to raise the house as little as possible before repairing, it raises a few questions in my mind:

    1. How to best integrate lumber? If there is enough height to slide in a 2x6, I feel that I should tie it in so the 2x and the sill act as a single unit and have a little lateral resistance - such as mounting right angle braces in the bottoms of the 2x's before setting them in mortar.

    2. How much higher than level do think I'd have to raise the sills to be able to lay down new mortar? For example the gable end of my house will get raised 2" on one corner and not at all on the other. It's a little hard to visualize if I would need to lift the entire length of sill off the foundation or just lift from the low side until level, then chip & re-pack as much mortar as I can reach.

    If I'm not making sense, I'm happy to sketch.
     
  7. Jun 10, 2011 #7

    oldhome

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    Nealtw - how long did the raising take? Did you put low profile jacks on the foundation? I can't visualize how you transferred to entire load to the foundation.

    I was thinking of building cribbing and using needle/carrying beams. The house has a bump out addition on one side so I have 4 different walls to deal with. Most of the house is post & beam, so the corners will all have point loads.

    Every time I think it through, I come up with another location that will need a jack...
     
  8. Jun 10, 2011 #8

    nealtw

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    Posts will be a different problem. We lifted the floor with beams added beside the bearing wall, we ended up cutting out parts of the sill and set the end of a 6x6 on the foundation the other end was 8 ft into basement and blocked to level. As the jack was within 6 inches of the foundation the foundation took 15/16 of the weight. How are you planning to lift posts.
    We did this with a finnished basement but we had 2 feet between cieling and floor. The center wall could not be moved so we raised the joists off the wall instead.
    To level the foundation we cut up every scrap of plywood around treated them green and spaced it up. We added bolt extentions to bolt it down and did some artfull cutting to a 2x10 combed fasia to add to the outside to hide it all.
     
  9. Jun 10, 2011 #9

    nealtw

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    oops forgot the question; 3 weeks!
     
  10. Jun 10, 2011 #10

    oldhome

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    No posts to worry about (but plenty of other things.) The house is a bit of a hybrid - it's balloon framed, but all the floor joists are 3x6's that are either notched into the sills, mortised into the beams, or simply resting on the ledgers w/no notch or nail. This house would have been built at a time where balloon framing was becoming common, but some builders were a bit reluctant to go along...

    With stud walls, it would normally be easy to lift the gable end of my house - just run a beam across the bottom of the all the joists and let the joists lift the sill. But, with the joists notched in place, I imagine that lifting them might only lift the floor.
     
  11. Jun 10, 2011 #11

    nealtw

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    Some what below the floor height let in a 2x10 into the studs so it is flush with the studs and bolt 2 more onto that and you have a beam to lift with. Between the beam and the floor add 12 x12 blocks of plywood about 2" thick and bolt them to the studs to stop the beam from rolling. Add 2x4 braces from the outside of the beam down to the studs near the sill to keep everything straight, and braces from lower studs to the floor joists for insurance.
    Everyone worries about lifting a house, that it would be unstable, all we did was jack one jack 1/8 or 1/4 and put in spacers and set it down and went to the next jack.
     
  12. Jun 11, 2011 #12

    oldhome

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    If you are talking about studs, you must have a pony wall above grade? I have 2' of brick above grade, the sills rest on the brick, and the floor joists notch into the sills.

    Sounds like you braced everything, which is something I'm mapping out in my mind right now. I have less framing in the basement to brace to, but I should still have some options. I will probably block between the joists to stiffen things up.
     
  13. Jun 11, 2011 #13

    nealtw

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    I missed the part about the brick , sorry. Just as well, cutting into all those studs would have been a problem anyway.
    Keep in mind the house we worked on was 8 years old and the owner was the builder and a building inspecter, he had the plans and knew where the bearing points were and how big the footing were. We planned the job for a year. We talked the a few engineers for pros and cons and only got cons from them witch we used to identify problems to solve. I hope others will join in here to help identify problems for you to solve or help you solve them.
    I suppose you could remove some brick and jack up the sill as it is 6x6 but we haven't addressed the foundation condition or the footings, perhaps the first order would be to consider underpinning the jacking points.
    Keep in mind when you have solved all the known problems the big one is just around the corner, what about porches, decks, stairs, chimneys, plumbing and of coarse rot?
     
  14. Jun 11, 2011 #14

    oldhome

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    All good concerns. The good news is that the wood is in reasonably good shape. There is the normal amount of joist & beam checking, and the spots with real issues have been identified. A section of beam has been identified for partial replacement, but anything suspicious already has a post. I will probably run a length of timber below the one really stressed beam.

    The subsidence of the foundation has happened over 100 years, and a number of contractors including two structural contractors have seen the stone foundation and pretty much said "not too bad, I've seen a whole lot worse." I wasn't really thinking about using the foundation as a lifting base, I was thinking of building up cribbing inside and out and running needle beams between the two. If I do put a jack on the foundation, I will only do so on the more stable wall.

    I figured that I would mortar up the most weathered stone walls to help them hold together when they get unloaded. Cleaning out and mortaring the gaps seems pretty straight forward, but I wonder about using far runnier grout which if introduced through gaps up high, will go wherever gravity takes it. It might do a better job of binding things up. Only hesitation is that I've often heard that old stone foundations really want softer mortars with more lime, because stone walls relying on a mortar that will give and put up with the settlement that occurs over the years, and because it will let water pass which alleviates the lateral forces of hydrostatic pressure.

    Plenty to think about, but I'm happy to hear more about what I might be forgetting.
    Believe me, you won't find a guy more grateful to be told that he's wrong.
     
  15. Jun 13, 2011 #15

    nealtw

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    I know nothing about stone foundations, I hope others will be along for that discussion.
     
  16. Jun 15, 2011 #16

    oldhome

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    Can anyone comment on the risk of the stone foundation giving way when the the house is raised and its compressive pressure on the foundation is removed? Does it take a disaster of a stone foundation for this to happen or is it a common concern?
     
  17. Jun 29, 2011 #17

    nealtw

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    I am surprized no one has anything to say here.
     
  18. Jun 30, 2011 #18

    oldognewtrick

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    I'd suggest calling a structural engineer if you have any questions about the integrity of the foundation. It will be money well spent.
     

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