8/10/2023 0 Comments Building a flat roof house![]() Traditional homes often have sections of flat roof-over shed dormers, above porches and garages, and on balconies. Of course, you don’t need to live in a modern house to deal with a flat roof. Yet for historic Modern-style buildings like This Old House’s Cambridge TV project, flat roofs are at the core of the architecture, meant to reflect the broad horizontal lines of the natural landscape. Add "hurricane clips," metal brackets that fasten the truss ends to the wall caps, on both sides of all trusses.Flat roofs aren’t architecturally logical, as rain and snow will shed much more quickly off a sloped roof. Nail the trusses to the ridge board use a level to keep the ridge board level the length of the roof. Set a ridge board in the tops of the trusses to connect them from end to end. Raise other trusses to the opposite end of the roof. Use a level to get it vertically plumb and fasten it to the walls through the truss bearing point with framing nails and a hammer. Lift the truss upside down and let the roof workers set it upright. Use at least three people for this - one on each side of the roof with a 2-by-4 board with a notch on top to hold the truss and one (or preferably two) on the roof to set the truss upright and fasten it. Lift the trusses to the roof, one at a time. The last space may be slightly less than 24 inches Step 9 Use the blade of the square, which is 24 inches long. Mark truss points 24 inches apart to the other end of the roof. Measure 23 1/4 inches in from the end of the wall to mark the outside edge of the second truss, then mark it 1 1/2 inches wide (use the 1 1/2-inch wide tongue of the framing square to mark that space). Start at one end of the roof and mark 1 1/2 inches in for the first truss. Step 8īuild the number of trusses needed to span the roof from end to end, spaced 24 inches apart. Adjust the wall caps if needed to level them. Use a level to make certain the wall tops are level so the bearing points of the trusses will be the same on both sides. (Brace the walls temporarily if removing the joists weakens them). Remove the roof joists from wall to wall the bottom chord of the truss will replace those. Use a pry bar or roofing scraper to peel off any roof paper/gravel or membrane covering, then pry off the plywood or oriented strand board (OSB) decking. Remove the covering and decking from the old flat roof. The finished truss should have two slopes, a flat bottom and braces that make a W shape. Turn the truss over and add gussets on all connections on the other side. Cut those braces and fasten them with gussets. Mark those quarter points and make four braces, two to fit from the peak to the quarter point on the bottom chord and two to go from that point to the rafter halfway between the bearing point and the peak. Measure to the center of the bottom chord, directly under the peak, then measure half that distance on each side. The gussets fit across the rafters just below the ridge board slot (some gussets are made with a ridge board slot). Drive the spikes in with a hammer to secure the gussets to both rafters, then add nails in all the nailing holes in the gusset plates. Remove the spacer and secure the peak and the two side bearing points with metal gussets, which have spikes on them. Mark the angle the rafters form across the bottom chord and cut it to fit. Set the plumb cuts together with a 2-inch (actually 1 1/2 inches thick) spacer board between them to duplicate a ridge board, with the bottom chord level between the rafters. ![]() Step 5Ĭut one pair of rafters with a circular saw at those angles and lay them on a flat surface with the bottom chord between them. Go back to the plumb cut and take off another 3/4 inch so two plumb cuts will have a gap for a ridge board. Add a foot to provide an overhang or eave and mark an end or tail cut, like the plumb cut but with the point of the square at the top of the board. ![]() Multiply that differential by the rafter span, half the width of the roof, to calculate that bearing point. Use the "length of common rafter per foot of run" to determine the length from the plumb cut to the end of the bottom chord, where it will rest on the top of the wall. ![]()
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