My house is sloped at least 1/8" per 1' along the front side. It also has long horizontal siding. So if windows are installed level it may be pretty noticeable. Leveling the house is not an option. So I wonder how can I minimize visual effect of the difference in levels between house and windows.

Should windows be installed parallel to the siding (and be out of level like old ones) or should they be exactly level (and what do I do to minimize visual effect)? Or should they be installed lets say with 1/16 angle - is it still ok?

  • I assume you have satisfied yourself that there is not a serious structural problem with this tilt?
    – bib
    Oct 4, 2012 at 17:02
  • What do you mean by 1/8?
    – bib
    Oct 4, 2012 at 18:35
  • I meant 1/8" per 1'
    – Uncle Meat
    Oct 4, 2012 at 19:00

2 Answers 2


Installing opening windows out of plumb (out of level), will make them hard to open and close, and may affect their ability to seal well. If the windows are fixed, this is less of a problem.

If you install them level, the most noticeable issue will be the top and bottom, probably not the sides. You can address this by being creative with casings, the molding around the windows. If you put a shallow triangular pediment across the top, it will mask the angle difference between the window and siding.


An alternative is a curved facia board at the top, or any other combination that breaks up the horizontal line.

The bottom could be handled similarly, but there is less tradition of decorative moldings or pediments at the bottom of things. A straight, stepped molding might also break it up.

stepped molding

SUPPLEMENT: Based on the additional information, 1/8" in one foot is not a lot of lean. I would still hang them plumb and mask it with the moldings. You could rip cut the molding on a slight angle to split the difference. Also, having the moldings NOT end at the edge of a siding board makes variances harder to notice.

window trimmed

  • Depending on the type of window, I don't see how out of plumb, but square would be a big problem. Out of square is definitely not to be done. Not sure if OP means 1/8" per foot (1:48) or actually 1:8 (crazy!) If actually 1:8, ignore this comment.
    – bcworkz
    Oct 4, 2012 at 18:25
  • @bcworkz Out of square is disastrous. Assuming all are square, out of plumb on double hung will cause the windows to bind on the sides. They "fall" toward the side the top leans to. Similarly casements will either tend toward "falling" open or "falling" closed (like doors out of plumb), and strain the hinges and mechanisms (or be hard to crank). Early on they should all work, but get harder as they age and friction sets in. The less lean, the less problem. Awning windows would not be affected much.
    – bib
    Oct 4, 2012 at 18:35
  • Sorry for not being clear on 1/8. I updated the question. I wonder if 1/16" per 1' out of level may still be tolerable. That would give only 3/16" difference on 3' windows. Probably not very noticable.
    – Uncle Meat
    Oct 4, 2012 at 19:07
  • Another factor is size/weight of the operable part of the window. For a 1:48 slope on an average sized window, the out of plumb stresses are minimal. Even so, I'm inclined to install it plumb and disguise the misalignment as bib suggests. I raised the question more as a point of discussion than endorsing out of plumb installation. I hope I did not cause any confusion.
    – bcworkz
    Oct 5, 2012 at 20:35
  • @bcworkz You are right that the amount of tilt is important. It is less of an issue than it seemed at first.
    – bib
    Oct 5, 2012 at 21:26

Always install your windows level and plumb to make sure your window functions properly. Adjust your trim or siding if you have to but don't unloved your window it won't function correctly.

His video had good information that I found helpful. Hope it worked out. Here's a link:


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