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Interior finish trim around windows with double stud walls

georgecarvill | Posted in Green Building Techniques on

So we are on the home stretch. The interior sheetrock is hung to the edge of the rough window open boxes. Windows are installed and low-expansion foam fills the spaces. 

So what kind of a window sill and sides and top? Sheetrock for three and wood for the sill? Other ideas? 

The articles I have found talk about flashing and other basic window installation details. But I don’t find anything about finishing.

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  1. charlie_sullivan | | #1

    We did sheetrock on three sides and wood on the sill (aka stool). I think it looks nice. Just make sure that you aren't relying on a wide wood board for air sealing, since it will expand and contract.

  2. onslow | | #2

    Mr. Carvill,

    Here is a link for a Trim-tex product that might be helpful. I know I regret not springing for the detail on my own deep wall to window openings.

    There may be competing products if Trim-tex is not a locally available brand. There is one additional thing to be considered if the drywall in the window bay is yet to be applied. The openings are most likely not truly square to the set window edges. If you are visually trained, having the window to drywall reveal vary in width will be a constant irritation. ( yes, 30 years in graphics takes its toll)

    The drywall contractor warned me from first meetings that if I was going to be fussy about the windows it would be very costly. The crews are paid by the sheet and speed is paramount. We settled on me being responsible for truing out the openings prior to the crew getting to each floor. Armed with thin luan underlayment patches and cardboard shim stock, I trued the mounting plane on three sides on many windows and all four on ones where my wife didn't plan on plants. The cats have had other ideas about what gets sat where.

    Not every window surround reveal is perfectly matched to other windows, but each window is consistent on the three or four sides. Be aware that you can get drywall in 5/8,1/2, 3/8, and 1/4 if you look hard. My rough openings and corner details created a bit more than average variance. It is not necessary to make a full corrected surface to attach the drywall. I settled on patches that provided leveled anchoring points every 12-15" depending on the window size and drywall thickness. The 1/4" is quite easily distorted if a screw is placed anywhere but on a leveling pad. 5/8" is pretty stiff. Putting cabinet knobs in the center of scraps of drywall used for checking the heights as you go makes the process a bit less taxing. Some openings required three thickness of drywall to balance the reveals.

    Being overly anal, I also squared the openings to the window plane to make the sills look "right" as well. If the opening's drywall splays outward a bit, at least the sill is easier to fit. If it pinches toward the room, the sills come out like dovetails. With 8" deep openings willywobble intersections on the sill/wall would bug me too.

    Last notes, I have a textured finish on the walls which might have fought a bit with the tear off feature. If you are going with a smooth wall finish, the strike point for mud thickness will likely be just fine. I am doing very thick sills out of local fir for a southwestern-ish feel which means the depth is subject to potential cupping over time. A trick I used for keeping deck stair treads from cupping was to put three to four slots with a circular saw on the undersides. The stopped cuts didn't show, but provided relief from the aggressive cupping deck stock is prone to. If you are painting out everything, I would recommend using a higher density MDF stock and paint the under sides at least one coat. An of course, shim the sills to match too.

  3. GBA Editor
    Brian Pontolilo | | #3


    Window trim options are virtually unlimited. Charlie's suggestion is a popular one for windows in thick walls and the look is clean, perhaps a bit modern, but it depends on the specific details. With drywall replacing a lot of wood, it's also a more affordable option. Here are some links to see how that can look and how to execute it. There's not much for trim carpentry on GBA. I suggest you search FHB for more ideas and lots of how-to on trim.

  4. georgecarvill | | #4

    Thank you both. Yes, I'm planning on wood for the stool. Probably some 5/4 local oak finished with tongue oil. I figure that goes in after the sheet rock, not before.

  5. Expert Member
    Akos | | #5

    If your windows are deep, make sure you use either quarter sawn wood or put curf cuts on the backside to avoid warping.

    Putting the wood over drywall you get a cleaner look as you need less/no trim around to hide the gaps.

    Budget option is to use pre-finished 3/4" flooring with matching stair nose piece for the end. Lots of choices for the wood and finish, no need to stain/clear coat and quicker to install.

  6. seabornman | | #6

    I wanted a more traditional look, so I built a "box" consisting of jamb and head extensions, stool, and trim. Finished them first and then installed using a few double ended nails on each side to connect the extensions to the wood window frame, and nails through the trim into the stud. I then added an apron under the stool. It worked fine and looks great, however each box had a slightly different depth or was inconsistent in depth so each box was unique.

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