This story shows you how to build a temporary support for the ceiling for use while installing a new window.
If your new window will be wider than 3 feet, you'll have to remove more than one wall stud. That could cause the wall's top plate -- and the ceiling -- to sag. If the ceiling joists are perpendicular to the wall and thus rest on the wall frame's top plate (see the illustration below), you must temporarily support the joists. Install the support no farther than 3 feet from the wall.
If the joists run parallel to the wall, supporting them will not help shore up the wall. Use the method shown on the opposite page. Use the same method if your home is built with old balloon framing, which has no top or bottom wall plates.
Build a temporary support that is several feet longer than the new window opening. Buy enough studs so you can place them about 16 inches apart.
About 2 hours to build a temporary support and wedge it into position
Tape measure, hammer, level, circular saw, handsaw, drill with screwdriver bit
Basic carpentry skills
Cover the room's floor with a drop cloth. You may choose to remove the drywall or plaster before building the temporary supports.
2x4s, 16d nails or 3-inch screws, shims
Mark the bottom and top plate for studs every 16 inches. Attach the studs to the plates by driving nails or screws. Add a second top plate. To keep from scraping the ceiling, add a scrap of carpeting to the top plate (see box below). With a helper raise the wall and tap it into place. If the fit is not snug, tap shims under the bottom plate.