Size of Rough Opening for Door or Window

Question

When installing doors and windows in a new construction house, how much bigger do I make the rough opening than the actual size of the door or window?

Answer

This is something you should check with your local supplier. I found big differences in rough openings, especially between window manufacturers. I'll give you the rules of thumb.

Exterior doors with sills: allow an extra 2" for width and 4" in height over the nominal size. Example: for a 36"x80" door, the rough opening should be 38"x84" with sill.

Exterior doors without sills and interior doors: allow an extra 2" for the width and 2½" for the height over the nominal size.

Bifolds: the finished opening is the size of the nominal size of door. Example: for a 30"x80" bifold, the finished opening is 30"x80". So allow for the thickness of the drywall or whatever finish to be installed. This holds true for a vinyl floor, anything thicker than that, allow extra. For ¾" hardwood allow an inch; for carpet allow a good inch. There is height adjustment on these things (within reason) so better high than low.

Windows - vinyl and aluminum: check with the supplier for rough openings. There should be about 3/8" clearance around the entire window. When nailing the flange, only nail the sides and bottom. Don't nail the top, at all. When the siding is applied later it will hold the top in place. This allows the framing to settle without taking the window with it. Most windows manufactured around here (the west coast of Canada) require the rough openings to be 1" under the nominal size. Windows in eastern Canada have totally different clearances for their nominal size, so it is very important to check the rough openings for the doors and windows from the supplier. If the rough opening is correct, the door or window will fit. If not, disaster!!

Headers for windows and doors: It used to be so easy before they changed the lumber sizes to 1½"x3½" from 1 5/8"x3 5/8", etc. Headers were as follows: 4' opening 2 - 2x4's; 6' - 2 - 2x6's; 8' - 2 - 2x8's; 10' - 2 - 2x10's; etc. Now most framers just use a double 2x10, tight underneath the top plate for all the lintels for all the lintels 8' and under to support a roof and one floor. Over 8', it is considered a beam and its size has to be determined from tables in the code book. For spans 2' and under, no lintel and its size has to be determined from tables in the code book. For spans 2' and under, no lintel is required when supporting just the roof. In fact, the studs can be placed on 2' centers, that's in Canada anyway. I wrote an article on the Building Code can be placed on 2' centers, that's in Canada anyway. I wrote an article on the Building Code and I tried to stress the point of asking questions from the inspectors about items like headers or lintels or lintels, depth of footings, snow loads in your area, etc.

Dave