# How to trim window after adding rigid foam between studs and drywall?



## jbrah (May 29, 2018)

I'm renovating a room, and to mitigate the thermal bridging across the studs, I'm covering the interior edge of the studs with 1/2" rigid foam board (it's closer to ~0.55" thick). Looks like this:









I'm fairly clueless about windows and trim, so not sure what the best approach is here, and figured you guys would have some good ideas.

This is the old trim:









Another shot, with the paneling removed (cool wall, eh?):









And here's what the window casing(?) (not sure if I'm using the correct term) looks like:

























The casing sits 3/8" - 1/2" proud of the studs. So once the studs are covered with 1/2" rigid foam, the casing will be flush to just slightly inset relative to the rigid foam. 1/2" drywall is going on this wall.

I just want some basic trim, nothing particularly fancy, and I'm not concerned about having a window stool and apron; basic trim along the bottom would be fine, whatever's easier. Not sure how to approach this. Do I need to extend this casing out to be flush with the drywall? Just cut strips of plywood and brad nail it into the existing casing? What about the thin trim piece circled in red in this pic:









I guess that needs to be removed and replaced with something similar, but ripped wider so that it's flush with the drywall? It's actually 1/8" shy of being flush with the casing, which seems odd, since that gap wouldn't be covered by the perimeter trim, leaving that sliver of casing exposed. I'm guessing that was an oversight when the trim was installed?

In terms of sequencing, does any of this need to be done prior to hanging the drywall? Or can I hang the drywall and cut out the drywall using a rotozip with guidepoint bit, tracing around the outside perimeter of the casing? There's a small gap between the casing and the studs around the entire perimeter (which I'll fill with canned window and door spray foam after removing the deteriorated fiberglass insulation), so even when the studs are covered with rigid foam board, the guidepoint bit will still have room to trace around the perimeter of the casing. And then extend that casing out, as described above, to be flush with drywall?

Thanks in advance for any insights and advice.


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## Nealtw (Jun 22, 2017)

I would plan on replacing the trim you have circled with a board that match to outside of the drywall which you will nail the trim to . If you want backing for the edge of the trim furthest away from the window, figure out where that will be and add a 1x2 for that. 

Like this looking down on the right side


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## carpdad (Oct 11, 2010)

Nealtw is talking about adding an extension jamb. I would remove the circled bead also. Then filling the gaps in the studs, foam board then drywall. Drywall to the old window jamb and finish the drywall. Then measure to the vinyl window and make a frame then finish attaching the trim to the square frame. I'm talking about preassembling the jamb and the trim and just slide it into the opening. You have to make sure the frame is square so will have to adjust the gaps. Measure the jamb cuts close to the window but I think you can leave as much as 1/8" gap and finish with caulk. Jamb can be prepainted also. Dry fit the assembly then remove and caulk the window to old jamb joints for more air seal then nail in the assembly. Homedepot has a stock of thin boards to make the jamb, or just use 1x stock if covering the window that much is ok with you.


And merry christmas to everyone! That's another over with.:smile:


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## jbrah (May 29, 2018)

carpdad said:


> Nealtw is talking about adding an extension jamb. I would remove the circled bead also. Then filling the gaps in the studs, foam board then drywall. Drywall to the old window jamb and finish the drywall. Then measure to the vinyl window and make a frame then finish attaching the trim to the square frame. I'm talking about preassembling the jamb and the trim and just slide it into the opening. You have to make sure the frame is square so will have to adjust the gaps. Measure the jamb cuts close to the window but I think you can leave as much as 1/8" gap and finish with caulk. Jamb can be prepainted also. Dry fit the assembly then remove and caulk the window to old jamb joints for more air seal then nail in the assembly. Homedepot has a stock of thin boards to make the jamb, or just use 1x stock if covering the window that much is ok with you.


OK, let me see if I understand the steps and sequencing correctly.
1. remove the circled trim in the pic in the OP
2. you mentioned filling gaps in the studs - you're referring the seam where the jack studs meet the wall studs? Those are already sealed (spray foam for the larger gaps, and polyurethane caulk for tiny gap or no gap seams).
3. apply foam board to studs around window
4. spray foam perimeter of window frame (between window frame and wall framing)
5. drywall
6. cut out around window frame (seems like using a rotozip to cut out drywall around the window frame would be easier than precutting the drywall before hanging it)
7. you mention finishing the drywall - do you mean tape and mud?
8. At this point, I need to make an extension frame to bridge the existing frame to the inside-room-face of the drywall. Kind of like what this guy does: 





Is that pretty much correct? If so, I'll focus on getting things ready for drywall (spray foam perimeter of window frame, and behind outlet boxes, and install Rockwool insulation), then drywall, then worry about the details of installing window extension and decorative casing (what I called trim in the OP, but I guess is more properly referred to as casing).

Also, why does the existing framing/jambs have a groove? Arrows in pic point to this groove.


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## jbrah (May 29, 2018)

Do I have the parts labeled correctly?









What's confusing to me about this diagram is that it looks like the extension jamb butts up to the window itself, as opposed to the wood framing around the window, i.e., in the below pic, the window framing the arrows point to. Doesn't that wood framing need to be extended out to the interior face of the drywall?


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## carpdad (Oct 11, 2010)

Forget about the old window jamb. It was probably factory made and who knows why the grooves? Factory labor was cheap so maybe the designer thought that is a sign of quality? Since the new window was attached to it, it becomes part of the house now. I would just air seal that gap with a caulk and frame over it.
That video is half of my thought. I don't see the guy squaring the extension frame but I guess he already checked the rough opening for square? Those little shims may be hint. Your rough frame (the old window jambs) may not be square so I was thinking you should check it and figure out what the gap should be to fit new, and square, extension jamb. I would nail the trims as well to the new jamb which would make it easier to square the trim corners. Your drywall should be finished and even painted, like the video, but don't try to lay the trims flat to the wall. Drywall is never perfect. Install the new frame, center it to the window and you can nail through the trims to install. Extension jamb does not necessarily need nails or screws. 

Sorry for getting back late with the reply. But it should help with other projects.


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## Nealtw (Jun 22, 2017)

jbrah said:


> Do I have the parts labeled correctly?
> 
> 
> 
> ...


 That is what we do here


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## jbrah (May 29, 2018)

carpdad said:


> Forget about the old window jamb. It was probably factory made and who knows why the grooves? Factory labor was cheap so maybe the designer thought that is a sign of quality? Since the new window was attached to it, it becomes part of the house now. I would just air seal that gap with a caulk and frame over it.
> That video is half of my thought. I don't see the guy squaring the extension frame but I guess he already checked the rough opening for square? Those little shims may be hint. Your rough frame (the old window jambs) may not be square so I was thinking you should check it and figure out what the gap should be to fit new, and square, extension jamb. I would nail the trims as well to the new jamb which would make it easier to square the trim corners. Your drywall should be finished and even painted, like the video, but don't try to lay the trims flat to the wall. Drywall is never perfect. Install the new frame, center it to the window and you can nail through the trims to install. Extension jamb does not necessarily need nails or screws.
> 
> Sorry for getting back late with the reply. But it should help with other projects.


OK, I think I understand. Apologies for being slow on the uptake; my first time dealing with windows.

OK, so the sequence would be:
1. remove the circled trim in the pic in the OP
2. apply foam board to studs around window
3. spray foam perimeter of existing wood window frame (between wood window frame and wall framing)
4. drywall
5. cut out the INSIDE perimeter of the existing wood window frame. In other words, the opening in the drywall should be the same size as the white vinyl window frame.
6. finish drywall
7. caulk around perimeter where white vinyl window frame meets existing wood window frame
8. make a square extension frame, attach trim/casing to it. When installed, this extension frame butts up against the white vinyl window frame (partially covering it, depending on how thick the jamb material is).



carpdad said:


> I would just air seal that gap with a caulk and frame over it.


Which gap are you referring to? The existing wood window frame/jamb has a gap around its perimeter, where there is currently some decrepit fiberglass insulation; I'll remove that and spray foam this gap. And per your earlier, post, I'll caulk the white vinyl window frame to the existing wood window frame prior to installing the extension frame.

I checked the existing wood window frame - it's just very slightly out of perfectly square. So I guess the idea is to attach shims to get that opening square. Then make a square extension frame to fit that shimmed opening.

Thanks for the advice!


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## carpdad (Oct 11, 2010)

Just 2-3 things.
1. Drywall to the old window jamb. Any gap should be covered by the trims.
I forget if your photos show the sill? That could be wider gap than what your trim may cover, so you may want to add 1x or so before drywalling. Leave enough room for bottom sash stops, flanges or handles and your fingers for lifting.



2. Even if your existing opening looks square, I would still make the extension jamb little narrower on all sides to leave some room to play. Also make the extension little shorter so you don't run out of room. Even if there's 1/8" gap, you can caulk it. So if 1x extension covers too much of the window sides, then you use thinner stock or plane down the 1x you have, or even plywood. I think you should be able to nail the trim to 1/2" stock to hold everything (maybe use glue as well) then nail the trim to rough framing. If there's a gap between the trim and the drywall, use a shim as a backer for nailing - so the trim doesn't get pushed out of place, esp the corner joint. Then caulk the gap and spot paint. If using a nail gun, air or electric, make sure other fingers are at least couple inches away. Thin nails can bend away from the target all by themselves.



3. If you caulk the joint between the vinyl window and the old jamb, that seals for air. Do this right before you're nailing in the extension and you don't have to worry about insulating any gap that would be behind the new jambs. That's not much empty air for losing insulating value.


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## jbrah (May 29, 2018)

carpdad said:


> 1. Drywall to the old window jamb. Any gap should be covered by the trims.


This has been a point of confusion for me this entire thread (again, apologies for being slow on the uptake here).

Should I drywall to the outside perimeter of the old window jamb or the inside perimeter?










Initially, I thought drywall to outside perimeter and attach new extension frame to old jamb, but once I realized the new extension frame should butt up against the white vinyl window frame, it seems I should drywall to the inside perimeter (covering the old jamb with drywall, and leaving opening in drywall that matches inside perimeter of old jamb).

So just wanted to get some clarity on this point.


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## Nealtw (Jun 22, 2017)

jbrah said:


> This has been a point of confusion for me this entire thread (again, apologies for being slow on the uptake here).
> 
> Should I drywall to the outside perimeter of the old window jamb or the inside perimeter?
> 
> ...


 They cheated when adding the vinyl windows, they should have removed the old wood jam and installed a much bigger window, so now pretend that that old wood is just the rough framing. 

You are just removing the 1/4 round and replacing it with a jam extension.


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## Nealtw (Jun 22, 2017)




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## jbrah (May 29, 2018)

Nealtw said:


> You are just removing the 1/4 round and replacing it with a jam extension.


This part I understand.

What's not clear is whether the old wood jamb gets covered by drywall or not.



Nealtw said:


> They cheated when adding the vinyl windows, they should have removed the old wood jam and installed a much bigger window, so now pretend that that old wood is just the rough framing.


Meaning, I should drywall over that old wood jamb, correct? Then the opening in the drywall would match the inside perimeter of the old wood jamb.


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## Nealtw (Jun 22, 2017)

jbrah said:


> This part I understand.
> 
> What's not clear is whether the old wood jamb gets covered by drywall or not.
> 
> Meaning, I should drywall over that old wood jamb, correct? Then the opening in the drywall would match the inside perimeter of the old wood jamb.


 Yes, go back to this picture from above, the orange is foam board, the brown is 1x2 to nail the trim to and the grey is drywall. Then you have jam extension out to the drywall and then the trim. :wink2:I missed an r in covers.


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## carpdad (Oct 11, 2010)

Squinting at the photo, I think I see little bump on the edge of bottom sill (part of the old window jamb). If it sticks out, it should be chiseled/cut away with razor, etc. It's fine to leave that edge rough since new trims will cover.


There will be little gap between vinyl window and the old jamb. The other side as well? These gaps must be filled against air with low expansion foam (low!) or stuffed fiberglass. Stuffing with fiberglass is fine. You're not aiming for insulation, to block the air flow. Same with all other small gaps.


The old jambs, that you arrowed with inside and outside edges, are flush with your studs and other frames. So the drywall can go over them without problem. You don't have to put screws into the old jambs, just into the studs. Sheets don't have to be cut exactly to the old jambs. Easy would be to cut the sheetrock first roughly with 2-3 access. Screw in the sheetrock then cut to the old jamb. Use the saw to cut the short sides then cut the surface with a razor for snap off. If the drywall is off, even by 1/2", and lot of old jamb showing, it's ok because the trim will cover.


It's funny. Just searched whole page of youtube "sheetrocking around the windows", there is nobody showing the basic method. You may have to look at sheetrocking in general, learn area specific things and apply to your case. One thing is, it's best if you use whole sheet over the windows, esp since it looks like one window. Butt joints become thicker because of taping/compounding. These will interfere with trim sitting flat against the wall. Start there and see if you get too much waste. It may be worth the waste not to have a joint around the window.


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## jbrah (May 29, 2018)

carpdad said:


> There will be little gap between vinyl window and the old jamb. The other side as well? These gaps must be filled against air with low expansion foam (low!) or stuffed fiberglass. Stuffing with fiberglass is fine. You're not aiming for insulation, to block the air flow. Same with all other small gaps.


I removed that quarter round trim and yeah, there's a gap between the vinyl window and old jamb. Up to 1/4" in some spots; too large for caulk, so I'm going to use Great Stuff Window and Door spray foam.



carpdad said:


> The old jambs, that you arrowed with inside and outside edges, are flush with your studs and other frames. So the drywall can go over them without problem.


The old jambs are a little proud of the studs; once I apply foam board to the studs, the old jambs will be flush. Yep, I'll drywall over the old jambs, thanks.



carpdad said:


> Sheets don't have to be cut exactly to the old jambs. Easy would be to cut the sheetrock first roughly with 2-3 access. Screw in the sheetrock then cut to the old jamb. Use the saw to cut the short sides then cut the surface with a razor for snap off. If the drywall is off, even by 1/2", and lot of old jamb showing, it's ok because the trim will cover.


I've got a rotozip, so it should be easy enough to cut out the drywall by tracing the rotozip's guidepoint bit around the inside perimeter of the old jambs. 



carpdad said:


> It's funny. Just searched whole page of youtube "sheetrocking around the windows", there is nobody showing the basic method. You may have to look at sheetrocking in general, learn area specific things and apply to your case. One thing is, it's best if you use whole sheet over the windows, esp since it looks like one window. Butt joints become thicker because of taping/compounding. These will interfere with trim sitting flat against the wall. Start there and see if you get too much waste. It may be worth the waste not to have a joint around the window.


Yeah, for sure I'll use whole sheets. The amount of wasted sheetrock will only be a few $ (and even that can be used in the future for patches), easily worth it to avoid the extra joints and extra labor of finishing those joints. But I guess I'll have a horizontal joint where the horizontal sheet touching the ceiling meets the horizontal sheet touching the floor - they will meet to the left and right of the window. But no joints above or below the window.


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## carpdad (Oct 11, 2010)

If the old jambs are little proud, don't assume the foam board will take care of it. I think it would be better if you can chisel/plane shave the difference (check the surface again for any nails still there?). I think it would be fine if you remove even too much. Drywall doesn't have to be screwed to the jambs and jamb/trim assembly will not depend on the old jambs to sit flat on the finish wall.


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## jbrah (May 29, 2018)

carpdad said:


> If the old jambs are little proud, don't assume the foam board will take care of it. I think it would be better if you can chisel/plane shave the difference (check the surface again for any nails still there?). I think it would be fine if you remove even too much. Drywall doesn't have to be screwed to the jambs and jamb/trim assembly will not depend on the old jambs to sit flat on the finish wall.


The old jambs were a little proud of the studs. Now that I've applied foam board to the surrounding studs, the old jamb is 3/16" - 3/8" recessed (depending on particular location around window). I was thinking I'd cut strips of some 3/16" ply I have and nail it into the old jambs just to get them closer to flush with the foam board. But given your point about the drywall and new jamb/trim assembly not depending on the old jamb, maybe measuring, cutting and applying those strips would just be a waste of time?


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## carpdad (Oct 11, 2010)

Depends on your worries:smile:. If a gap, just leaning on the drywall without thinking could break it while working. Or maybe compounding/sanding/painting? Once the trim goes up, there is no such risk. With a new construction, done by the usual habits, there is less risk but yours has that old jamb. Just be little extra careful.


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## jbrah (May 29, 2018)

carpdad said:


> Depends on your worries. If a gap, just leaning on the drywall without thinking could break it while working. Or maybe compounding/sanding/painting? Once the trim goes up, there is no such risk. With a new construction, done by the usual habits, there is less risk but yours has that old jamb. Just be little extra careful.


Yeah that unsupported area is a bit of a concern. Maybe I'll just spray some foam on it. Trimming it flush with the surrounding foam board would be easy. And that would support the drywall so the edges don't break off if there's pressure on them prior to the trim being installed. 

Spraying and cutting cured foam is a lot quicker than measuring and cutting thin strips with a circular saw (no table saw, yet). Plus I'd get a little R-value from the foam.


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