View Full Version : prehung door install - floor level?

06-19-2012, 06:40 AM
I'm installing a prehung door in a basement. When I check the floor for level in the rough opening, the hinge side of the opening is about 1/4" lower than the latch side. Most tutorials I've seen just say to throw the prehung door in the opening and fix the jambs as you go. However, if my hinge side is low and I plumb and attach that jamb first, the latch side jamb will be too long to get a the proper reveal (and level) at the top of the door...right?

This Old House says to shim up the hinge side jamb, which would account for this issue I'm imagining. But why doesn't anyone else discuss this? I'm considering trimming the 1/4" off of the latch side of the door rather than shimming the hinge side since I'm using laminate flooring under this door. The jambs are both 1" longer than the door bottom to allow for carpet clearance. Is it typical to trim the jambs down a bit when laminate is going under the door so there isn't a huge gap between the finished foor and bottom of the door? If so, how much is normally trimmed off? I'm thinking I can trip the latch side by xx" + 1/4" and the hinge side by xx".

06-19-2012, 06:58 AM
If the bottom of the jam will sit on top of the laminate flooring, then trim the latch side. You don't want to shim up the hinge side.

What size room is the door for and does it have a dedicated cold air return or an exhaust fan? The inch of space under a door is often used for air return or make-up air. If that is not a factor, trim both sides to suit.

06-19-2012, 07:13 AM
Prehung doors are usually installed just as they come on a level floor. Your floor is not level, so you can trim or shim wherever, and however, you want to as long as the flooring covers your work.

Gary Swart
06-19-2012, 10:08 AM
If the floor is not level, there is no way you can fit a rectangular door perfectly in the space. DUH. The door should be hung with the sides plumb to the jambs. The top may or may not be perfectly square to the opening, but that can be covered with trim. This leave the bottom of the door to be dealt with. You can trim the bottom of the door so the gap will be true to the floor. It won't be square, but it will look OK and the door will open and close properly.

06-19-2012, 10:18 AM
You can trim the bottoms of the door jambs if needed.

The main concern is that the hinge side is vertical with a level. The hinge side is attached first, and then the opposite side is raised or lowered to fit the top of the door squarely. The "reveal" should be the same across the top of the door, and on the latch side.

06-19-2012, 02:10 PM
Weather you shim one side or trim off the other does not matter but the most important thing is that the door opening is square. The door jambs must be plumb and the top level. I would prefer to trim off one side (or level the floor). If the bottom of the door needs to be cut that is easy enough but it is not so easy to add on to a door. If the door trim is in place and you add floor boards such as laminate you may not need to cut the door off but you might. Some people like to cut the flooring around the casing but I think that looks messy. The door trim should be cut off the thickness of the flooring. If you do not want to remove the trim, there are special jamb saws for this purpose and they work great. Some hardware stores rent them.


06-20-2012, 05:53 AM
I ended up trimming 1/4" off the latch side jamb and it worked out perfectly. Typical example of me trying to overthink something rather than just going with my gut and doing it. Thanks for the help.

06-20-2012, 07:08 AM
quote; The top may or may not be perfectly square to the opening, but that can be covered with trim. This leave the bottom of the door to be dealt with.

That will leave you with a door with a "crooked" opening across the top and almost EVERYONE would notice it when the door is closed. AND, you might have to move the latch plates to compensate. You install a "RECTANGULAR" prehung door, plumb AND level, by adjusting the jambs as needed.