How do I install a pre-hung door in a rough opening that's too wide?

Question

I'm replacing an interior door -- including the original jamb -- in my house with a new 30" pre-hung door. With the jambs, the new door is 31 3/8" wide. However, the original rough opening is between 32 1/2" and 32 3/4" wide, leaving me a big gap between the old frame and new jambs. The hinge-side stud is straight and plumb, so I'll probably not have to shim that side by much (if at all), which will leave the bulk of the gap on the latch side.

Can I fill a gap that big with shims, or should I think about nailing a 1x4 to the latch-side stud first? If I use shims, I think I would need several to make up the right thickness: is there a trick to holding them in place while I secure the door jamb to them?

Answer 1

From you description, it sounds like you have a hair over 1 1/2 inches of extra space to make up. If this is correct consider this method. Place a full 1x4 (or whatever the depth of the wall may be) on both sides, as long as the new door frame will still fit comfortably in the new opening. When ever possible, I like to mount the hinge side to a solid petition without excessive shims. This makes it more solid without having to bridge a large gap with your finish nails, and makes it a lot easier to perfectly plumb the hinge jam. I often replace the center hinge screw on the jam side with a longer matching screw that will attach to the jam. This does a few things for you. One, you don't need as many nails, gives a much more solid feeling and sounding door, and gives you a tool to fine adjust the plumb if necessary.(especially on heavier solid wood doors. Just like with security screws on an entry door. After you are sure you are happy with the plumb on the hinge side, simply use visual to get an even gap on the top and latch side, in that order. You can then use shims on the latch side and shoot your finish nail just below your shims. this keeps the shims from dropping as you work down the jam. i don't usually shoot through the shims because they often split and I may want to slightly adjust them before the trim casings are installed.

Answer 2

Before you fix the door to one side, leaving a bigger gap on the other side, make sure your casing trim will completely cover the larger gap. If either side of the door opening is on a narrow wall (e.g. the end of a hallway), you'll also want to make sure your door is centered on that wall just for aesthetics.

Also, there's no need to use an entire 1x4 and definitely no need to plane it down -- that's what shims are for. Just use blocking that's 1/4 to 1/2" thinner than whatever gap you end up with and shim it out until it's snug. Make sure your blocking is behind the hinges (if you are using blocking at all on the hinge side), and behind the latch, in addition to wherever else you're nailing in the jambs.

Answer 3

Fixing the new jamb directly to one side is definitely the right approach.

I'd put the new frame in without fixing it and then shave the wood to fit the gap on the other side. Take the frame out and then fix the filler piece to the wall.

Then fix the new frame to into the opening using shims to get it 100% (or as near as you can) vertical, directly to the frame on the hinge side and the filler piece on the latch side.