I'm now installing 2 large patio door sliders that require the frame heightened. When I resize the framing opening, is it possible to have the door/window fit perfectly on all four sides with no gap? There will be no insulation, and I can make it square, strong, and level.

The reason I ask, is besides extensive shimming for securing the window in, there's even more complicated shimming required for the inside. Bit hard to explain, but there's basically plastic trim on the aluminum window frame that has to fit exactly to within maybe +/-3 millimeters on pre-routered 1x4s and 2x4s that act as the inside sill sides and top etc.

If the shims are strong and secure, wouldn't they similarly have the power to bend the frame if the house shifts?

The inside casing or windowsill ( not sure the terminology, the 4 pieces you see on the inside when it's done - 3 in the case of the sliding door as it ends up flush with the flooring) fit 1x4s perfectly on the sides and 2x4s on the top /bottom. They need to be shimmed very strong as people will be leaning on them and hitting them whatever, and the tolerances are very tight as it has to screw into that plastic track I mention that's attached to the inside of the window frame. Attaching it to the rough buck opening directly is way stronger and easier than having to make tons of shims that are required to be screwed into the frame and get the correct clearances.

I'll also end up with the window frame screws and these 'trim' screws very close to each other and risk splitting the shim in half. Additionally, the nail on flange is quite close to the edge of the frame and there's is not much for the nails to bite into. Having a tight fit in the frame would solve all these problems in one step.

Photos of Windows with similar shimming: http://s22.photobucket.com/user/excipio/media/Mobile%20Uploads/image_17.jpeg.html http://s22.photobucket.com/user/excipio/media/Mobile%20Uploads/image_16.jpeg.html

Regarding shims, the frame has five predrilled holes on each side and four on the top, with specially designed screws for that purpose. With a gap of 15 mm, only about half of that screw actually be in the rough buck. I'm also still not clear on how 14 strong secure shims tight in the window would not damage the frame if The house shifted, while a smaller gap with smaller shims (say 5mm, or even none ) would. Zero shams and having it very strong seemed more appealing than 14 shims. Additionally, the base of the window has to be exactly flush with the non-existent flooring. The subfloor isn't even in yet, just the old cedar planks and framing which themselves are not level.
Everything has to be calculated just so, and none of it's working out perfectly, or else flang nails and flooring start missing their mark. I realize everyone does it the Larg gap way, i'll do it that way to get it done. But that doesn't necessarily mean it's the best way to do it.


In this case, for a couple of reasons, I ended up installing them straight in with largish shims all the way around. One of the flange nails on one of the windows missed the frame, but it was unavoidable. Got it done and they look great and are pretty strong. Something that's been bugging me during this reform is how to make sure things are plum, level, and straight. I've used a string with a weight on it, a small right angle Square, a small bubble level, a straight piece of metal, etc. these all work to a point where they break down, and I end up using my sense of perception to get it pretty close. For example, on these sliding door frames: The bottom of the rough opening was bulging slightly in the top, and the front; The sides were slanted on the inside from front to back; and the top of the frame was warping up and slanting from the front to the back. None of my tools could indicate all of these problems and how to correct them when I was installing the frame. Worse still, as I was installing it the frame would warp to accommodate the different angles, throwing other elements off. There was no way to tell other than by Eye roughly, and I ended up just trying to average things out, and settle for pretty close. And I missing anything, is there some magic tool that makes it easy to install everything perfectly level straight and shimmed properly?

  • 1
    I agree tight is bad.
    – Ed Beal
    Commented Jan 21, 2016 at 21:08
  • Yes, rough opening.
    – TheNiceGuy
    Commented Jan 22, 2016 at 16:37
  • Part of my concern is that the entire nail on flange is only about 25 mm wide. There's about 15 mm gap between the frame and the window on each side, that leaves only about 10 mm for the entire seal of the window as well as the nails to bite into ( holes are actually quite close to the edge of the frame wood) . It seems preferable to have more flange overlap on to the woodframe allowing more sealant and grab for the nails.
    – TheNiceGuy
    Commented Jan 23, 2016 at 16:01
  • No window manufacturer would build a unit designed to fit framing tightly. Your approach is flawed, and you need to figure out why. I'm not exactly sure what the issue is that you describe. Maybe some photos of the extension jambs and hardware would help.
    – isherwood
    Commented Jan 25, 2016 at 14:09

1 Answer 1


It would be a mistake to install any window or door tightly in the framing. Houses move, and units installed tightly can get bound up and/or damaged.

Your window should be installed level and square by shimming the bottom and sides. It's usually best to not shim the top in case the framing above settles. The rough opening should be about 1 inch larger than the window in each dimension.

The plastic slots you mention are for the extension jambs (the pine boards you mentioned). They should be installed in a manner similar to the window itself, where you shim the corners from both directions to keep the joints tight. Also shim one or two points along the bottom to keep any object weight from causing sag.

None of this should be "complicated", to use your word. Work bottom-up and keep it simple. I like to have on hand 1-1/4" x 3" plywood shims in 1/4" and 3/8" thicknesses, along with tapered shims. Here's my basic procedure:

  1. Set the window in the rough opening, supported at each lower corner by a 3/8" flat shim (carpenter pencils also work well as temporary supports). Center the window horizontally in the opening and check level across the top or bottom. Adjust with bottom shims as needed, then fasten the bottom corners according to the manufacturer's instructions.

  2. Check square by measuring diagonally from corner to corner in each direction. Shim the top corners side-to-side until the dimensions match. Check plumb at the sides of the window. Fasten the window complete per the manufacturer's instructions.

  3. Install and shim the jamb in a similar manner, adding shims where needed to keep the joints tight. Optionally dry-fit the jamb components and build the box before installation.

  4. Insulate gently with fiberglass or low-expansion spray foam and be happy.

  • Nail on flange is only 1 inch wide in total, meaning all of the nails would miss the rough buck if I made the gap 1 inch. I added comments above, including that the bottom has to be flush with the flooring, which will be all thrown off if I put shims as you described.
    – TheNiceGuy
    Commented Jan 24, 2016 at 3:29
  • I didn't say to make the gap one inch. Please read again.
    – isherwood
    Commented Jan 24, 2016 at 22:01
  • This is the correct way to install a window / door Good advice Isherwood
    – Ed Beal
    Commented Jan 25, 2016 at 14:01

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