trimming door jamb

splice1

I just purchased a prehung door and was wondering how much to trim off of the jambs. There is no threshold and the spacing looks to be about an 1 1/2" extra on the new jamb. My floor unlevel by a 1/2". Never did this and don't want to screw up. The door is replacing an old existing door and is being installed over hardwood with no threshold. Thanks

DangerMouse

Hi! What type of heat do you have? Some types require an inch or space under the door to breathe.
Other than that, just measure 3 times, cut once.

DM

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splice1

I have forced hot water. My question is do I cut one side of the jamb a half inch shorter because of the floor? How much space should be below the door? Thanks

DangerMouse

There should be enough clearance at the bottom to swing freely above the flooring/carpet without snagging.

I'd remove the door from the jamb, (just pull the hinge pins) install/level/flush the jamb, then re-attach the door.

DM

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BigJim

Is the old jamb shorter on one side? Also take a look at the existing door and see how the bottom is cut, that will tell you how the new door should be cut if at all.

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Jim

tcleve4911

When you have to cut jambs at different lengths, this is one way of finding the proper length.

Take a 4' level and run it anywhere across the opening. I usually just put it at eye level so I get read it easily.
Mark each side of the wall.
Now measure down to the floor on each side.
The difference between the two measurements will be the amount you need to make one side longer that the other.

The space under the door should be 3/4" - 1-1/4" depending on heat and any rugs or transitions.

jlhaslip

Measured from the sub-floor, not the finished floor height.

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splice1

Thanks for the info. I really like the 4 foot level idea. Would all of you remove the door first even though it is prehung?

BigJim

You won't need to remove the door to cut the jamb, it will be easier with the door in the jamb. If you have to cut the door you will have to take the door out of the jamb. You for sure want the door in the jamb when you hang the unit as it is a little tough to get all your margins the same other wise.

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Jim

splice1

Thanks JUJU. I guess I'm more confused that if I cut the jamb shorter on one side to allow for the uneven floor. Won't the bottom of the door be uneven?? The door is a molded 6 panel door from Broscoe.

BigJim

Yes, the margin at the bottom of the door will be 1/2 inch higher on one side than the other. It may be necessary to cut the door to the slant of the floor not only to look right but for the door to be able to open without the bottom of the door dragging.

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Jim

splice1

Yikes!!! Sounds a lot more difficult than I was hoping for. Can I cut a molded door?

BigJim

The bottom of the door isn't molded is it? Can you post a picture?

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Jim

Joe Carola

Why is it so difficult? All you have to do is cut 1/2" off one side of the jamb. Your sitting the jamb on top of an oak floor. If you don't like the 1/2" angle, you will have to cut the door 1/2' too nothing. Is it worth it? If so, cut the door nice and straight clamping a straight edge on the door with the angle and follow that with your saw.

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Joe Carola

carpenter man

Did you consider leaving the old jambs and trim in place and using the old door as a template ? You can cut the bottom of the new door if your floor is that much out of level . You can buy a door that is not pre hung and just replace the door without removing any of the old jambs or trim . You may have to mortise the hinges into the new door. That would be the only tricky part that requires accurate measuring . The old door would give you the correct spacing from the existing hinge locations . I have hung hundreds of new doors in new construction and replaced a ton of existing doors. I wish you luck !!