Things You'll Need
2 by 4 lumber
3-inch wood screws
Double-wall construction is done primarily to thicken the walls of a house to allow for plumbing or thicker insulation. The second wall of a double-wall construction is not load bearing but is primarily for aesthetic purposes only. However, it is essential that you follow a few tried-and-true methods when converting your single-wall construction into a double wall. The average do-it-yourself homeowner can complete this project in one to two days, depending on the size and scope of the project.
Measure out from the existing single wall 3 to 4 inches on each end of the wall and snap a chalk line across the floor perpendicular to the wall. Using a plumb bob, transfer that mark up to the ceiling.
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Attach a floor plate and ceiling plate--flat 2 by 4s on the floor and ceiling-- using 3-inch screws. Make sure that the screws are inserted directly through the ceiling plate and into ceiling rafters (rafters are usually 24 inches apart). Find the rafters with a stud finder and mark them lightly with a pencil. A stud finder is an electronic device that reads depth density in a wall or ceiling. It is used by sliding the device across the surface of the wall or ceiling, at which time an alarm will sound off when the device crosses a ceiling rafter or wall stud. Space the floor plate screws 24 inches apart as well. Align the plates to the inside of the chalk line rather than to the outside of the line. Remember that the line represents the outermost part of the new wall.
Mark across the floor plate in 24-inch intervals. This will be your center mark for placing your wall studs. You will cut each stud individually because the ceiling and floor may not run perpendicular to each other (the floor or ceiling may be sagging).
Measure the distance from the floor to the ceiling at each mark, beginning against the left side of the new double wall. Cut the first stud and place it on the center mark on the floor and attach using 3-inch screws. Drive the screws in at an angle, one on each side of the stud. Using a level, plumb the 2 by 4 to the top plate and attach in the same way. Continue until the wall is complete.
Add blocking--horizontal 2 by 4s between each stud--across the wall at about the middle of the wall. Cut the 2 by 4 blocking 22.5 inches. Insert the blocking between the studs and attach using 3-inch screws. The blocking should be staggered across the wall to allow each block to be attached from the backside of the stud. Add insulation in between the studs and cover the wall with drywall or paneling to suit your needs.