Doors – Removing Doors Before Installing Sliding Patio Door Frame

A router (along with a special guide) can be used to cut part of the inset you need, but is not the easiest tool to use if you are not experienced, and it does not cut square corners, which still require a chisel to finish.

Using a chisel does take care and practice, but it is not beyond the reach of even an amateur if you are willing to do a test piece first and then go very slowly.

You need to draw the opening with a sharp pencil (or and awl). Many people use a utility knife to cut the outline to slightly deeper than needed, then use a small, sharp chisel, following the grain of the wood (in this case toward the top and bottom, not across the door) taking very thin layers out until you are deep enough.

It does not need to be perfectly flat at the bottom of the channel, just the right depth at the ends with no high spots in between.

If you practice on a scrap of wood first, you may be surprised that you can do it.

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.