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Doors & Windows

Interior PreHung Door Installation w/ unlevel door frame/floor

Hello! 

I'm trying to install a new interior prehung door but the frame/floor is unlevel. I have watched some of the videos online but found it was unclear on how much to cut the door jam to compensate for the unlevel floor. How would I measure this and decide how much to cut off the jam?

Thank you!
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Posted 2018-08-18T18:10:08+0000  by Kmallay13 Kmallay13
 
What I would do is lay a level across the opening and then using shims, make the level perfectly “level.”  From there carefully measure up from the top of the level to the header above the door opening on each side.  To that number ADD back the thickness of your level (since you measured from the top) and SUBTRACT 3/8”-1/2” from that to give yourself a little room for adjustment and that’s the overall length of each leg of the jamb.

Then measure the gap between the top of the new door and the bottom of the jamb, it’s typically about 1/8”  Take the new door out of the jamb and hang jamb in the opening ensuring the top is level and the sides are plumb and parallel.

Put your level back on the floor and use shims to make it “level” again.  Measure up from the top of the level to the bottom of the top of the jamb on each side.  Again ADD back the thickness of the level, subtract the 1/8” (or whatever gap you measured).  From there you have to take into account the thickness of the finished floor.  Typically you’ll want the door to be about 1/2” above the finished floor.  Whatever number you come up with, subtract it the previous calculation.  Measure down from the top of the door on each side, mark, connect the marks, and carefully trim the bottom of the door.

Make sense?  If not, I can go into greater detail.
Posted 2018-08-21T03:48:33+0000  by Adam444
 
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