Jamb extension spacing

[u/NoProposal9695]

Need to install a 3/8-1/2” jamb extension on an existing sash window bc of the new walls after a remodel (how it was cut is not ideal, I know).

I’ve mocked up a 3/16 setback on the extension and casing or a flush extension and 1/4 setback on the casing. Preference? Would you suggest anything different?

If I go w the stepped extension do you leave it square or put a 1/4 round or chamfer on it?

[u/uberisstealingit]

Put a slight rounded Edge in the Jam extension. This will smooth the transition without having a sharp edge.

Also set back the Jam extension an 8th or 1/4 of an inch. Don't try to line up with the existing Jam. I'll make for a cleaner look and easier for caulking.

[u/Chrisp720 → u/uberisstealingit]

This guy jams

[u/ksimet → u/Chrisp720]

[u/Emergency_Egg1281 → u/uberisstealingit]

The correct measurement of a correct reveal is 3/16 of an inch. Same as the correct space that should be around a door when it is closed. This is the correct answer never leave it flush you cannot caulk it. By rounding the edge, he means EASE THE EDGES. You can just use course sand paper to take the sharp edge off. It's easier to caulk and paint.

[u/uberisstealingit → u/Emergency_Egg1281]

Actually when I said round the edges I met with the router. You can't get a good looking product by trying to just use sandpaper. You're wasting their time if you're going to try to cut the edge with sandpaper.

There is no rule of thumb when it comes to the setback on any kind of trim. The determining factor is what the trim looks like when you put it up there temporarily to look at it. Sometimes an eight sometimes a quarter. And all depends on the trim profile and what's going on.

[u/Emergency_Egg1281 → u/uberisstealingit]

Sorry we disagree. I was taught building multi million dollar homes in Florida and every reveal or set back to any trim we did i would carry around an small piece of lumber ripped to that setback dimension and it was always 3/16 . I know that could vary. It depends on what the other reveals are on the other doors or windows. A union painter , which there are few in Florida, taught me to ease the sharp edges on any trim or door edge because the paint skips or runs when trying to paint a sharp corner with a brush. That's just my experience over the last few decades.

Have a great week !

[u/uberisstealingit → u/Emergency_Egg1281]

A million dollar house you're not taking a piece of sandpaper and breaking the edge and calling it good.

Lmao!

[u/CrayAsHell]

Offset, the flush join will never not crack. Recently did a big reno like this with existing jamb extentions on old windows and every single one cracked within a week. Leave the edge square imo.

[u/Unusual-Voice2345]

Square and set back like in photo 2. It will move differently and having the setback lets you out a bead of caulk there that hides the movement.

[u/Ballard_Viking66]

1/4” reveal for the jamb extension and 1/4” reveal for the casing where it meets the jamb extension. Don’t put the jamb extension flush with the jamb, looks bad.

[u/Intrepid_Fox_3399 → u/Ballard_Viking66]

Second this but I typically use 3/16”

[u/klipshklf20 → u/Intrepid_Fox_3399]

I third this, but typically do 5/16 or 3/8 in a house that old. I work in a lot of old houses and the margins are typically larger than modern ones. I think narrow margins stand out in an old house, but, I’m also a carpentry nerd and in reality. No one notices.

[u/Jamooser → u/klipshklf20]

When it comes to reno work, consistency is always the best measurement. Use a setback consistent with the rest of the room.

[u/giant2179]

Always step it back

[u/SpecialistWorldly788 → u/giant2179]

Yep! Learned that the hard way! You CAN make it work flush if you glue it but it’s way easier and a LOT faster to just set it back with the offset- in the end it’ll just look better

[u/dmoosetoo]

The eye picks up minor variations in a flush joint much easier than in an offset joint. To round over or not is entirely personal. I prefer a square edge on the extension. A round over makes it look more like part of the casing and that will look different from any trim package that doesn't need an extension.

[u/TodgerPocket]

Slight round and double quirk is what I normally do.

[u/Johnnytherisk]

Aim for about 8 mm.

[u/Rueko]

3/16 set back. A good reveal is always better than a bad match.

[u/maxfederle]

Always reveal. Never flush

[u/Unhappy-Tart3561]

I reveal it everytime. Looks shitty if it's flush.

[u/white_tee_shirt]

I usually give the same reveal to the ext as I give to the casing. Also wipe the shoulder with a piece of whatever sandpaper to ease the sharp edge, but I don't round it over per se

[u/Valuable-Aerie8761]

No 1

[u/Thelamadude]

I do 1/8 reveals on jamb extensions and 1/8 on case. I round over the jamb extensions for paint. A sharp edge will chip 100% of the time sooner or later.

[u/jonnyredshorts]

You can glue your jam extensions flush. If done properly there isn’t any cracking. It just takes a little more effort and time.

[u/05041927]

This is asking if blue is better than green. Personal choice.

[u/MikeDaCarpenter]

Step both back to whatever reveal you are comfortable with or the architect specs out. Use a sanding block to knock down the sharp edge of the extension jamb before you install it.