Extended Jambs

[Rich Riddle]

Have any of you ever extended a jamb? It seems from reading that many folks offset the new jamb. Is that what you recommend?

[Bruce Wrenn]

For doors, I offset extension. This allows for use and access of standard knob. I generally make rough opening an extra 2" wider than normal. Set door, put in insulation, then fasten extensions thru sides of jambs. Finish up insulation. For windows, I pocket screw on extensions

[Jeff Bartley]

Yes, 'offsets' are commonly called the 'reveal'. Some like a 1/4" reveal, some like a 3/16th" reveal. Extention jambs are widely used, especially in renovation work!

[Jerry Miner]

Yeah---I spent a lot of time as a finish carpenter and have done many jamb extensions --can be done flush, but that means more fussing and sanding to achieve true flush surfaces. Quicker and easier to offset, leaving a small reveal--can be as small as 1/8"--just so it looks like an intended offset, not a "miss" at trying for flush.

[Neil Gaskin]

We almost always set an extension jamb with a reveal. Setting the jamn and extension flush with each just doesnt look as good in my opinion.

[Jim Dwight]

When I got a pre-hung door for an expansion room I got it from the place my builder uses. He did the rooms through drywall but didn't do finish carpentry (I was saving money). So I went where he goes because he said it was cheaper (I think he was right). I got the pre-hung with the trim I wanted to use (versus the narrow cheap stuff on the pre-hung doors at Home Depot or Lowes). I was surprised by the jambs, however. They were the slip fit kind that extend to fit the opening. Trim was on both sides of the jamb. You put one side in then slipped the other side into the first side and nailed it home. Really quick and no extension jamb required regardless of wall thickness (within reason). My walls were standard except the lumber was several decades old.

For a door, I would consider getting this sort of jamb so you won't need the extensions.

[Neil Gaskin]

When I got a pre-hung door for an expansion room I got it from the place my builder uses. He did the rooms through drywall but didn't do finish carpentry (I was saving money). So I went where he goes because he said it was cheaper (I think he was right). I got the pre-hung with the trim I wanted to use (versus the narrow cheap stuff on the pre-hung doors at Home Depot or Lowes). I was surprised by the jambs, however. They were the slip fit kind that extend to fit the opening. Trim was on both sides of the jamb. You put one side in then slipped the other side into the first side and nailed it home. Really quick and no extension jamb required regardless of wall thickness (within reason). My walls were standard except the lumber was several decades old.

For a door, I would consider getting this sort of jamb so you won't need the extensions.

We call those split jamb doors. They work great in the correct applications but I'm not a huge fan. They're harder to shim properly and at least locally, we end up needing to remove the trim in most cases because it is not installed with the best care or get's knocked around in shipment.

Our lumber and trim suppliers will make a custom jamb width and pre-hang the door leaf for a reasonable charge.

[Peter Quinn]

I make them a lot like Andersen extension jambs, 1/8" reveal, with a rabbit along the leading edge to act as a locator. Depending on the amount of extension they can be nailed and glued on through the face, pocket screwed from the blind side, or screwed on through the face if the casing reveal will cover the holes.

[roger wiegand]

So for you who like to add a reveal with the extension, if you're making one the right size to start with, do you step it back? My house has some odd size door openings and I just made the jambs to the correct width. I thought they looked fine that way, but now you've got me thinking I missed an opportunity to add a bit more interest to it.

[Mel Fulks]

When it is a fix something ,do it as you see best for situation. Good custom work might have a door rabbet on both sides because even when you know which side will get the door, interior decorators sometimes change it. When there will be
raised paneling double rabbet can make both sides more alike

[Bill Adamsen]

When the mfg puts a radius on the inside of the existing jamb, a reveal is about the only acceptable solution. For windows, if there's a sill, that goes in first. I don't think I've ever done an extension window sill - can't imagine that needing to be done.

[Kevin Bourque]

Sometimes I'll put a bead on the extension piece and it looks like beadboard when its mated up.

[scott vroom]

We did a remodel a few years back where we replaced 1/4" luan paneling with 1/2" drywall. Customer was unwilling to pay for new pre-hung doors with custom jambs so we glued/pin nailed some 1/4" pine lath flush with the existing jamb and sanded flush. Looked fine.

Same job, different room.....we removed 1/4" luan paneling and replaced with 5/8" sheathing (earthquake country, old home with no exterior sheathing) plus 1/2" drywall. 2 doors were affected and I convinced the customer that extending the jamb 7/8" would look crappy; she agreed and we installed 2 new pre-hung doors with custom width jambs.

[Peter Quinn]

So for you who like to add a reveal with the extension, if you're making one the right size to start with, do you step it back? My house has some odd size door openings and I just made the jambs to the correct width. I thought they looked fine that way, but now you've got me thinking I missed an opportunity to add a bit more interest to it.

If you can, making the jambs the proper width is always my preferred option. But sometimes, particularly with windows in old work and entries that is simply not possible. Too much trim involved on the exterior, you change the interior depth, it has to be rectified. Or you install a stock home center door in an old house with plaster walls that approach 1" thick, and diagonal sheathign that is nearly 15/16, and 2X4's that actually measure 4"....it adds up to way more than the 4 9/16" that is ubiquitous. Then you have to make adjustments. I would not go out of my way to step back a full and proper width jamb, unless you are talking a really wide jamb width that is being broken up a bit, there I'm usually making a panel jamb if the style allows, or using plywood if not. As mentioned often the factory jambs are radiused on the leading edge, or the old work jambs have been or become radiuses on the leading edge over time. Its really hard and not worth the effort IMO to try and create a flush condition. Often the edges of new factory jambs are primed, so no good glue surface, you will always get creep if you sand flush, the paint will show a line over time, the step back is IMO a much better condition.

In the garage I built a few years back I used Andersen windows. Standard jamb width was like a solid 1/3 cheaper or more than factory applied jamb extensions, and custom jamb width was just silly. Standard jamb width is 4 9/16" for 2X4 construction....they had better get on the stick over there in window land, they are in cold country, that standard is going away except maybe in warm places, here if you want to meet code with insulation its either spray foam, or foam panels, or filling a 2X6 framed cavity with fiberglass which is usually cheaper. The only places getting framed 2X4 in this area are dumps, and nobody is building them. Its 2X6 24OC, or SIP's, or foam behind the siding with 2X4 walls, but more often foam behind the siding on 2X6 walls. They make the stock windows one size, you want wider, you will pay a lot., or go with a custom fabricator, and pay a lot. So I installed them at 4 9/16" in a 2X6 wall cavity and some day I'll get around to building the jamb extensions. I built a large french in swing casement for the same structure, quotes were over $4K for that one so it made sense to make it myself, and I sure did make a full width jamb! Solid mahogany too, instead of FJP clad in vinyl. If I spec'd that quotes probably would have been over $6K!

[Larry Edgerton]

I make them a lot like Andersen extension jambs, 1/8" reveal, with a rabbit along the leading edge to act as a locator. Depending on the amount of extension they can be nailed and glued on through the face, pocket screwed from the blind side, or screwed on through the face if the casing reveal will cover the holes.

I have a pair of biscuit joiners, one has a special block on it with the fence folded in the up position to do the windows/doors, and the other is set with the fence down to do the extension jambs. They are set so when they work together they leave a 3/16 reveal. I have a basket full of 3" metal straps with holes in them, so I just put a touch of glue on the ex jambs, slip them in place, screw into the framing through the metal straps [1/4" thick] right next to the window to clamp. In about twenty minutes the clamps can come off, good to go, no fasteners. I got tired of the fasteners messing with you, either coming out the side or shifting the piece so I came up with this method. Works for me.....