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Siding installation question

kevinjm4 | Posted in General Questions on

This may be a dumb question but do you install siding level, or on same plane as sill plate/top foundation? In 36’ the house drops steadily about 1-2” (edit: actually it is 3/4”)  No cracks in the foundation nothing like that the house just sinking a little bit towards one side

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  1. Expert Member


    Not a dumb question at all. it's something everyone who renovates old building faces and the answer is: it depends.

    Where the decision becomes tricky is if the settlement is irregular or localized. If the whole building has settled consistently - the windows and soffit are also out of level, walls out of plumb - then I'd go with the plane of the foundation.

    Once you have taken that route, leave the level in your truck. No half-measures. Everything needs to be parallel or at 90 degrees to the foundation. Watch things like flashing terminations where the slope may allow water to run horizontally, and make sure to provide end-dams.

    1. kevinjm4 | | #2

      Hmmm. Well my windows are new, so they are plumb and square and there are four of them - 16 lin. ft. In total. Soffit slopes w/ building. Corner sheathing framing not plumb.

      So it really is a mixed bag for me. Perhaps because I am doing board and batten can help shed some light? I will do battens plumb - so they line up well with windows. Going to try to do corner plumb... not quite sure what to do with base belly band/water table trim board.

      And yes, it is a consistent steady slope. Thanks

      1. Expert Member
        Akos | | #3


        I would loose the belly bend, with windows that are plumb, it will be pretty hard to hide the angle.

        For the corners, you have to shim to plumb, it needs to be parallel to the windows.

        The eyes can only see parallel lines. As long as those are even, you won't notice slope.

        For the bottom, it might be best to put a large flashing over the foundation. You can use this to hide the foundation slope and use it as reference for your siding.

  2. Expert Member
    BILL WICHERS | | #4

    I’d go by my old rule for hanging shelving or running electrical raceway on a brick wall: unless the walls mortar lines are off a LOT (as in obvious to the eye), follow the lines in the brick. If your small thing is level and the wall isn’t, your thing will look wrong UNLESS the wall is off enough that it’s visible to the naked eye. Be most careful along visible lines like the top of the foundation wall and vertical corners on the building.

    If you’ve ever laid hardwood flooring, think the same way. Split the difference of any error to minimize the relative difference on each side. Follow other lines so things stay straight relative to each other. Try to get your cut lines in good places so that they don’t line up in odd ways or leave you with a tiny piece to finish a long run.

    Make sure all the flashing is right with your level though. Water will run down by gravity and it doesn’t care what anything looks like.


  3. natesc | | #5

    3/4" is nothing across 36'. Hang your water table and bottom wall flashing a little below the sill, and set them as level as your curvy boards let you.

    Siding is all about cheating. As with every aspect of building.

  4. kevinjm4 | | #6

    I should correct my post: building gradually slopes down 3/4” in 36’. Not 1-2” like previously thought. I put a laser on it last night.

    1. Expert Member
      BILL WICHERS | | #7

      3/4” over 36’ is only 1:48. That probably won’t be visible to the eye. I’d make it level, and be careful to match your windows which is probably the most visually significant part of the job.

      The only place I could see it being visible at all would be near the ground where you could hide it with some landscaping if it anyone noticed. Plant flowers or shrubs.


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