At least two good reasons exist to opt for two-by-six studs over standard two-by-fours for wall framing. Apart from the fact that a two-by-six wall is stronger, it provides more space for insulation, which protects a living space from cold outside temperatures and noise. Framing a door in a two-by-six wall involves a little extra work and expense because standard doorjambs are made for two-by-four walls.
Door Framing Overview
Whether you are framing a door for a two-by-four or two-by-six wall, the procedure is essentially the same. Start by erecting two king studs spaced apart by the width of the door (including the jambs), a 1/2-inch shim space on each side (used for plumbing the door unit during installation), and 3 inches for the combined thickness of the two jack studs. Cut the jack studs to the height of the door (including the top jamb) and a 1-inch shim space minus 1 1/2 inches (the thickness of the wall's sole plate). Install the jack studs against the inside faces of the king studs; you will cut out the sole plate between the jack studs before installing the door. Set and secure the header to the top of jack studs to span the top of the door opening. Install short studs, called cripples, above the header to connect it to the top plate of the wall. Standard doors are available in 30, 32 and 36 inches wide with a height of 6 feet 8 inches.
The Header
The cripples and header bear the weight of the structure above the doorway and transfer this load to the jack studs, which rest on the wall's sole plate and function as support posts. The size of the header is critical -- if it is undersized, the structure can sag. A two-by-six wall is most likely an exterior wall and therefore load-bearing; this means the header must be designed to bear the load above the wall, factoring in the header span, or width of the door opening. The header must be the same thickness as the two-by-six wall, about 5 1/2 inches. You can make it from nominal six-inch lumber (such as a six-by-six, six-by-eight, etc.), but many builders fashion their own headers by sandwiching cut-to-fit sheets of plywood between two-by boards to equal the dimensions needed.
Wide Jambs
The biggest challenge when framing a two-by-six door opening is that standard doorjambs are made for two-by-four walls. Some builders install standard jambs and add extensions to bring the edges flush with the wall, but that leaves a messy joint in the middle of the jamb. A better solution is to make your own jamb from one-by-eight lumber, ripping it to the actual width of the doorway on a table saw. Clear fir makes good jamb material, but you can also use pine or, if the budget allows, hardwood instead.
Squaring the Opening
Plumb the jack studs, using shims if necessary, and to level the header so that there is no more than a 1/2-inch variation in the opening from top to bottom and from side to side. This allows you to fine-tune the door's position by tapping cedar shims into the shim spaces between the jack studs and the side jambs; shims are also used between the header and top jamb to prevent the nails from bowing the jamb upward. If the rough opening is too far out of square, it is difficult to compensate with shims when you install the jamb, and the door may not open or close properly. Use a 4-foot level, and work slowly to ensure the best results.