Trusses are designed to span across large openings, without needing many interior support walls. The design is based on the fact that the junction of the top members creates a strong point because of the angle involved. When installed, the only way the boards can sag or fall lower, is for the foot ends to spread apart, allowing space for the top point to drop. Of course, the truss is assembled to prevent the spread of the foot ends. When properly done, it becomes a static unit, creating a vertical load only.
The interior braces are there to support the spans of the top cords and bottom cords. I prefer to use 2x6 members for top and bottom cords in a tru-ss to reduce internal bracing requirements.
To build the tru-ss accurately, you must first draw the tru-ss on the floor. Position the drawing to permit room to turn the tru-ss over. In other words, allow space for two truss-es on the floor.
STEP 1: Determine if you are building an “extended bottom cord” or “extended top cord” tru-ss. See the drawings below.
STEP 2: Pop chalk lines to make a rectangle on the floor that measures the width and height of the tru-ss you plan to build. Make sure the rectangle is square.
STEP 3: Measure over on the top and bottom and make a center mark.
STEP 4: Draw the entire tru-ss on the floor.
STEP 5: Cut the pieces and lay them in place on the drawing.
STEP 6: Make sure all the pieces fit correctly. When you are happy with the fit, mark these pieces as patterns.
STEP 7: Cut out as many pieces as you need for the number of truss-es you are building. Remember, gable end tru-ss-es are built differently because they do not span and they must provide framing for the gable end sheathing.
STEP 8: When you have all the pieces cut, lay a complete tru-ss in place on the drawing.
STEP 9: Layout the gussets on a sheet of plywood. You will need gussets for each side of interior truss-es and one side only of the gable end truss-es.
STEP 10: Make your gussets out of OSB or half inch plywood made with exterior glue.
STEP 11: Stack the OSB three or four sheets high and cut all of them at the same time.
STEP 12: Distribute the gussets around the tru-ss so they are easy to reach.
STEP 13: To build the tru-ss-es, use a top quality wood glue. Elmer's wood glue works great. Do not use construction adhesive because you want a tight, firm bond. I always use an air stapler and 1 ¾ “ staples when building tru-ss-es. I strongly recommend staples over nails.
Two or three people assembling the tru-ss-es makes the assembly process work much easier.
STEP 14: Place a liberal amount of glue at the joints, and along the members, the length of the gusset. On the first tru-ss, you may need to hold a gusset up or lay it in place and trace it to ensure your glue placement is right.
STEP 15: Lay the gusset in the glue in place over the joint. Don't let the gusset hang over any edge – top, bottom or side. It does not have to be flush on the edges. An inch from the edge is fine, just as long as it does not hang over anywhere.
STEP 16: Staple the gusset to the members below. Use plenty of staples. I place two rows of staples in each member, spaced about an inch apart. On the tru-ss end where the top and bottom cord meet, I would place 20 staples in the top board and 20 in the bottom board, at a minimum.
STEP 17: Continue around the truss stapling the gussets in place. BE SURE TO KEEP THE MEMBERS IN PROPER PLACE. This is best done by holding the members together while placing a staple or two in each member. After the first staples are holding the members in place, you can fill up the gusset with staples without worrying about the members moving.
STEP 18: When you have all the gussets on, turn the tru-ss over and apply the gussets to the opposite side.
STEP 19: Layout the next pieces in the pattern drawn on the floor and go again. Continue until all 20 inside truss-es are completed.
STEP 20: Now you are ready to build any gable end truss-es. These tru-ss-es are different to provide the framing for the gable ends of the house, and because they don't span anything, as they sit on the exterior walls.
STEP 21: Lay the bottom cords, top cords and the center upright on the pattern.
STEP 22: From the center of the truss, layout 24 inch centers across the bottom plate to each side.
STEP 23: Lay back toward the middle of the tru-ss 1 ¾ inches at every mark. This point is the long side of the uprights.
STEP 24: Transfer these dimensions to the bottom edge of the top cords on each side. A framing square is good for this.
STEP 25: When you have this point marked, measure from the bottom board up to the mark. This distance will be to the long point of the 2x4. Cut two boards this length for each gable truss and two lay in place.
STEP 26: After confirming the first boards are correct, just repeat the process for all the vertical boards.
STEP 27: When everything is assembled and fits correctly, place and staple gussets on one side only on this tru-ss.
STEP 28: For additional gable end tru-ss-es, lay all the pieces on top of the first end tru-ss and assemble it, using gussets on one side only.
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