Practical Shortcuts to a Strong Framed Roof

A roof frame of rafters in either shed or gable style makes an appropriately simple topping for the simple structures de scribed in this guide. A shed roof, a single deck that slants from a high wall on one side of a building to a low wall at the other, is especially easy to build. Each rafter extends over the whole width of the building, and the rafters must be thick and heavy if the distance is long. A gable roof, which rises from both walls to a central ridge beam, divides the distance in two. It takes longer to build, but it permits the use of lighter and less expensive stock for rafters—or even prefabricated rafter sets called trusses—and thus is a more common choice for the roofs of large cabins.

For both shed and gable roofs, the long boards used as rafters must be cut at angles to fit the top plates of walls, the ridge of a roof or the overhang of an eave. Where a rafter rests upon a top plate, it will need the notch called a bird’s-mouth to hold it securely. Where it meets a ridge beam, it will need a bevel called a ridge cut. Rafter ends that over hang beyond a wall are generally cut off parallel to the wall so that trim boards can be nailed to their ends. Cutting the special angles for top plates, ridge beams and overhangs can be a tricky business in large, complex roofs, but for the simple frames shown here they can be cut with out intricate calculations or special tools.

Before you cut the rafters, you must decide upon the pitch, or slope, of your roof. The decision is largely a matter of esthetics, except that certain roof coverings require a specified minimum pitch. Wood shakes or shingles, for instance, must be laid atop a roof that rises at least 4” for each foot of horizontal distance below it; metal panels or asphalt shingles can be laid at a minimum pitch of 2” per foot.

The distance between wall tops in a shed roof, or between a wall top and the ridge beam in a gable roof, is the span of the rafter. Most rafters are in fact longer than their span, to provide an overhang beyond the wall tops, but it's the span that determines the stock from which a rafter is cut. Ordinary rafters spaced on 16” centers—normal for frame construction—should be cut from 2-by-4s for spans up to 5’, 2-by-6s up to 9’, 2- by-8s up toll’, 2-by-10s up to 14’, and 2-by-12s up to 18’. Rafters spaced on 24” centers should be 2-by-6s for spans up to 6½’, 2-by-8s up to 9½’, 2-by-10s up to 12’, and 2-by-12s up to 15½’. (For roofs that must bear a heavy load of snow, see the chart.) If you are building a gable roof, you also will need a supply of joist stock: the walls beneath a gable roof must be tied together by ceiling joists to prevent the rafters from splaying or sagging.

Framing a Shed Roof

1 Marking the bird’s-mouth cut. Snap a chalk line down the middle of a rafter board and hold the board against the end of the building so that the chalk line touches the top plates of the high and low walls. Tack the board to the plates and mark the board at the top and outside edges of the lower top plate; extend the horizontal line at the top of the plate to the bottom edge of the board. At the high wall, mark along the inside face of the top plate, across the top of the top plate and to the edge of the board.

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2 Marking the overhang cuts. Place a carpenter’s level against the rafter board at the point you have chosen for the end of the overhang and draw a plumb line to mark the overhang cut. Re move the rafter board and cut it along the marks, then use this rafter as a template to cut the remaining rafters. Mark the high and low top plates for rafters on 16- or 24” centers and attach metal rafter anchors at the left edges of the rafter locations on the upper plate, at the right edges on the lower plate; for the two end rafters, attach both anchors to the locations of the inner face of the rafter.

3 Attaching the rafters. Set the rafters against the rafter anchors fitting the bird’s-mouth notches snugly over the top plates, and nail the rafters in place. On the two top plates of the other walls, which run parallel to the rafters, mark locations for cripple-studs 3½” wide, centered above each wall stud.

4 Installing Cripple studs. Working from inside the structure, hold a 2-by-4 flat against the out side of the top plate and the end rafter at each marked location. Plumb each 2-by-4 and mark it along the top plate and the bottom edge of the rafter, then cut the 2-by-4s at the marks and toe nail them to the plate and rafter.

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Framing a Gable Roof

89 1 Installing joists. Toenail joists, cut to span the width of the cabin, to the top plates of the side walls on either 16- or 24” centers, matching the planned spacing of the studs; locate the two end joists 1½” from the outside of the gable-wall top plates.

If the structure has an interior partition running across the joists, like the frame cottage, you can use joists only half as long as the width of the cabin. Butt the inner ends of these joists over the partition, toenail them to the partition’s top plate and tie them together with metal gussets, called truss plates.

2 Making temporary ridge-beam supports. Nail 1-by-2 cleats 1½” apart (the thickness of a 2-by-8 ridge beam) to protrude beyond the ends of two 1-by-6 temporary supports. Center and nail an assembled support to the inside of each end joist, with the top of the support 7½” lower than the planned height of the roof peak. Install diagonal braces between each support and an end joist. Cut a 2-by-8 ridge beam to the length of the cabin and mark it for rafters on either 16- or 24” centers.

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3 Raising the ridge beam. With a helper, center the ridge beam in the temporary supports. Snap a chalk line down the middle of a rafter board that's long enough to reach from the ridge beam to the top plate, plus any planned overhang.

4 Marking the ridge cut. With a helper, set the rafter board against the gable wall, with the out side edge of the top plate touching the chalk line and the top edge of the ridge beam touching the top of the rafter. Tack the rafter in place, mark a vertical ridge cut down the rafter board along the face of the ridge beam, then mark the bird’s-mouth and overhang cuts as shown, Steps 1 and 2.

Cut the rafter at the marked line and use it as a template to mark and cut the remaining rafters. Nail metal rafter anchors to the top plates next to all but the end joists, positioning them for rafters set against the ends of the joists. Mark the ridge beam for corresponding rafter locations.

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71 5 Nailing the rafters. While one helper holds a rafter to the location mark at one end of the ridge beam and another holds it to the top plate, butt-nail the ridge beam to the rafter. Nail the other end of the rafter to the joist with four 10- penny nails. Toenail a second rafter to the ridge beam opposite the first, and secure it to the top plate in the same way. Attach a second pair of rafters at the other end of the ridge beam and fill in the remaining pairs of rafters along the beam, fastening each rafter to the ridge beam, to a joist and to a metal rafter anchor.

6 Trimming the joists. With a circular saw, trim the corners of each joist flush with the top of the rafters, using edge of the rafter as a guide for the saw blade. Remove the temporary ridge- beam supports and attach cripple studs to the gable wails (Step 4).

Assembling a Set of Trusses

The easiest way to frame a conventional gable roof is to use a set of factory-built trusses, which eliminates the tricky jobs of installing a ridge beam and cutting angles in rafters. The trusses—zigzags of 2-by-4s fastened with toothed metal plates—span distances as great as 40’ without a load-bearing interior partition. Upper timbers called chords take the place of carefully cut rafters, while a bottom chord serves as the ceiling joist. Diagonal “webs” connect the top and bottom chords, transferring weight to the beams or top plates of the building. End- truss webs run vertically to accommodate sheathing and a ventilator.

When ordering trusses, specify the span between front- and back-wall top plates or eave beams, the length of over hang at the eaves, the size of the ventilator opening and the pitch, or slope, you want for the roof—generally at least 4 inches of rise for every foot of horizontal span. You will need adjustable scaffolding, available at rental agencies.

72a 1 Fastening the nailers. Attach framing anchors every 24 inches along the top plates (or, for a pole-frame cabin, eave beams) of the front and back walls; for the gable-end walls, nail 2-by-4 nailers to the plates 1½” in from the outside edges. The 1½” offset is handily gauged by holding a 2-by-4 block on edge and flush with the outside edge of the plates. Align the ends of the nailers with the outside edges of the front and back top plates.

72b 2 Erecting temporary scabs. To make scabs— needed to brace the end trusses—nail four 4-foot strips of the sheathing you will use for the cab in, to four 8-foot 2-by-4s. Nail two scabs to studs in each end wall about a third of the way in from front and back walls, with the sheathed half of each scab below the top plates. (For a pole-frame cabin see prev. discussion where the roof is framed before the walls, make scabs of unsheathed 2-by-4s extending from the ground to 4’ above the eave beams. Set them flush with each end of the cabin and brace them.)

Sheathe the end trusses with plywood and cut a ventilator opening in the sheathing.

73a 3 Rolling the trusses. Working with two helpers on scaffolding, set the ends of an end truss upside down on the top plates of the front and back walls and , with a 2-by-4 wedged into its peak, push the truss upright to the helpers. Walk the truss to the end wall, set it into position between the nailer and the scabs, and nail the scabs to the top chords and the nailer to the bottom chord.

4 Bracing the trusses. Roll up the second truss following the same procedure as for the end truss and nail it to the framing anchors on the front and back walls. Temporarily brace the second truss to the end truss with a 1-by-6 marked at 2-foot intervals and nailed to the top chords of both trusses. Nail a second marked 1-by-6 to the top chord on the other side of the ridge. Install the other trusses in the same way; where 1-by-6 braces adjoin, lap them over two trusses.

5 Plumbing the trusses. Loosen the scabs on an end truss, nail a long diagonal 2-by-4 brace to the ventilator framing and plumb the truss with a mason’s level. Once it's plumb, have a helper nail the brace to a stake. Fasten sheets of exterior-grade plywood atop the trusses, removing the 1-by-6 braces as you work. Then nail the 1-by-6s across the tops of the bottom chords to link the chords and add stability. If your structure is in a high-wind area, add 1-by-6 diagonal braces between the webs of each end truss and the bottom chord of the fifth truss from each end wall. Remove the temporary scabs.

Covering the Roof: Shingles, Shakes and Panels

Most cabins, like most houses, are roofed with asphalt shingles, but two somewhat less common materials should be given special consideration: wooden shakes and corrugated metal. Shakes, though expensive, provide the most appropriately rustic covering. Metal offers very practical advantages: economy, easy installation, fire resistance and , for areas subject to heavy snow, a slippery surface that sheds snow before it can build up.

The type of metal roofing illustrated below—called 5-V crimp because each panel has pairs of V-shaped corrugations, or crimps, at the sides and a single crimp in the middle—is particularly simple to work with. It is available at most large farm-equipment and building- supply dealers in panels 5 to 12’ long, in a variety of colors, in both aluminum and galvanized steel—aluminum is recommended for amateur builders because it's both light in weight and easy to cut and bend. Unlike other kinds of metal roofing, 5-V crimp does not require separate moldings at the eaves. The only special trim that you will need is a ridge roll—a rounded piece of aluminum sheet with flanges—to cap the roof ridge.

The 5-V crimp material can be used on roofs that have a pitch of at least 2” of rise in each 12” of horizontal span. Shakes require a pitch of at least 4 in 12, asphalt shingles 2 in 12. Roofs of lower pitch are difficult to make weather-tight without professionally applied “built-up” roofing. The methods illustrated below, simplified from those prescribed for year-round homes, are suitable for vacation and weekend cottages in moderate climates; in areas subject to severe icing and heavy snow, additional weatherproofing such as flashing may be advisable.

A Snow-shedding Surface of Aluminum

74 1 Preparing an end panel. After installing a roof deck—generally ½”, type C-D plywood in rows with staggered joints—and fascia boards, use tin snips to trim off the two outer Vs from one side of an end panel. Then make tabs to bend over the eave and gable by snipping 1” slits 1” in from each trimmed corner; snip similar slits into each fold of the three Vs remaining.

75a 2 Installing the first end panel. Starting from the end opposite the direction of prevailing winds, position the end panel so its slits are flush with the gable and eave edges of the roof, nail the middle V through the crown at two-foot intervals and fold down the edges of the panel. Drive roofing nails—the kind sold with attached neoprene washers—through the folded-down edges into the roof fascia boards at 6” intervals. Fold over and nail down the small tabs snipped at the Vs to close the ends of each V.

3 Installing intermediate panels. Working on the ground, slit the Vs at the eave edge as in Step 1. Then, on the roof, overlap the double Vs of the second panel with the Vs of the end panel; nail at the crown of each V at 1-foot intervals, and bend and nail the eave edge of the panel.

Add the remaining panels of the course in the same way along the eaves until you come close enough to the other end for its end panel, which is cut to fit and attached in the same way as the first end panel (Steps 1 and 2). Add additional courses up the roof as necessary, overlapping them at least one foot and trimming and bending the end panels. At the ridge, nail into the valleys—the space between double Vs— and hammer all Vs flat 6” down from the ridge to make a surface for the ridge roll.

4 Attaching the ridge roll. With tin snips, make 3” tabs in the rounded top of the ridge roll, at the ends that will fit over the gable peaks. Nail the flanges of the roll every 6” over the flattened Vs of the panels, and fold the tabs to close the roll ends. Fold the flange ends over, and nail them and the tabs to the fascia.

An Asphalt-Shingle Roof

76 Laying a pattern. In this simplified installation of asphalt shingles (a single shingle is shown in the inset), a ½”, type C-D plywood deck is laid with staggered joints and covered with 15- pound roofing felt overlapped 6” at the bottom edges. Fascia boards are not essential. If ice may be a problem, add flashing.

Along the eaves, lay a starter course of shingles from which 3” have been cut off the left edge; these first pieces laid should also have the three tabs trimmed off. Place the first course of untrimmed shingles over the starter course, and overhanging the eaves and gables ½”. Apply courses above so the lower edge of each shingle lies directly over the top of the cut outs of the one lower down. Begin the second course with a shingle trimmed by 4” at one end and begin the third course with a shingle trimmed by 8” (broken lines). The fourth course is the same as the first, the fifth the same as the second and so on to the ridge.

The ridge is finished with individual shingle tabs, bent to cover both sides. Start the job by nailing a tab at each end of the roof ½” beyond the gable to match the shingle overhang; over lap succeeding tabs 7”.

Laying a Shake Roof

1 Covering the edge. Shakes are traditionally laid over an open deck of 1-by-3 boards nailed to the rafters and , for the 16” shakes illustrated, centers spaced 7” apart—except for the lowest two rows, whose centers are 5½” apart. Lay the starter course so that the shakes overhang the eave by 2” and the gable by 1½”; space them ¼” apart and drive two nails per shake 9” from the bottom. Lay the first course right over the starter course, starting with a shake cut in half so that vertical joints are staggered by at least 1½”.

77 2 Laying remaining courses. Lay each shake to overlap the top 9” of the shakes under it. Overhang 1½” at the gables. Drive nails 8½” above the bottom so that all nails are covered. Lay the final courses at the ridge so that the top edges of alternate shakes on one side of the roof butt against the undersides of the shakes on the other side .

How to Split Shakes with a Frow and a Mallet

If you have a few cedar or redwood logs, you can make your own shakes fairly simply with a special cutting tool—available from specialty-tool sup pliers—called a frow. Saw each log into 16” sections and mark off ¼” intervals across the top of the section for each shake. Place the log section on sturdy supports, hold the frow firmly— with its sharp edge against the top of the log—and strike the frow sharply with a wooden mallet.

The log should split evenly and the shake pop free of the log, though you will probably need several attempts to discover the necessary force and rhythm. Do not try to split through a knot; instead, remove the frow and start at the next mark on the log.