How to Build Loft Style Trusses
A loft is almost a second story, but not quite. Lofts are found in houses, barns and industrial buildings and serve a variety of purposes. A true second story will have walls framed up on all sides with a roof on top. A house loft will be inside the roof of the basic house. Virtually all loft trusses today are factory-made; they are cheaper, stronger, require less carpentry skill to build and install and can be delivered anywhere. A homeowner building his own will need material, tools and excellent carpentry skills.
Choose a style for loft trusses. Options are open style or storage; both have a bottom chord or brace that rests on the house walls, rafters which slant to a peak, vertical braces called webs that form interior walls and diagonal braces from the bottom chord at the point of the web to the rafter. The open style has a wider opening and more headroom, but has ceiling slants on each side. The storage style provides square walls and ceiling, but with less head and side room.
Design the truss on graph paper if you are not an expert carpenter and truss builder. Put measurements and angles for truss elements on the paper to help you figure precise angles and connections. Show all pieces in their proper place with specific angles and lengths marked. Use this to lay out pieces when they are cut.
Measure the house from wall to wall to determine the width or span of the bottom chord; the rafter run will be half that distance. Select a style and cut two rafters to that pitch; the pitch or slope will be determined by the distance from the bearing point where the bottom chord rests on the wall to the peak, affected by the internal space required. Add any overhang or eave beyond the wall edge to the rafter length. A typical loft roof pitch might be 7/12, meaning rafters slope up 7 inches for every foot of run.
Cut a 2-by-4-inch bottom chord with a circular saw to the required length. Figure rafter angles and lengths using a framer's square and cut 2-by-4s to that length; leave a 1 1/2-inch gap between rafters at the top to hold a ridge board. Cut a top chord to fit horizontally between the rafters and a king post to go between the peak and the top chord. Cut vertical web boards and diagonal braces to length according to dimensions on your plan. Webs for an open style usually will be 8-foot studs, storage webs a foot shorter.
Lay out truss pieces on a driveway or other flat surface according to your design. Use a circular saw to cut an angle on the bottom chord to match the slope of the rafters at the bearing point, where the bottom chord will rest on the wall. Nail all joints together with a hammer and 3-inch framing nails.
Cut gussets or braces from 1/2-inch plywood; these can be either rectangles or triangles but must fit over all boards at joints. Make the top gusset to fit below the ridge board opening from rafter to rafter and over the king post. Screw gussets in place at all connections with a screw gun and 1 3/4-inch galvanized screws. Turn the truss over and screw gussets over all joints on the other side.
- Use a framer's square to figure rafter angles and lengths. For a 7/12 roof put the end of the square at the bottom of a 2-by-4 with the 7-inch mark on the short side of the square and the 12-foot mark on the long side, both at the top of the board. That will show the angle for the top cut where rafter meets ridge board.
- Use the table on the long side of the square to figure rafter length. For a 7/12, look under the 7. It will show 13.89, meaning the rafter has to cover 13.89 inches for every foot of run. Multiply 13.89 times the run (half the span) and add any desired overhang to get the total rafter length.
Bob Haring has been a news writer and editor for more than 50 years, mostly with the Associated Press and then as executive editor of the Tulsa, Okla. "World." Since retiring he has written freelance stories and a weekly computer security column. Haring holds a Bachelor of Journalism from the University of Missouri.