Framing a valley with trusses is a simple matter of attaching a series of progressively smaller trusses to the top chords of the trusses of the main roof. The main-roof trusses do not have to be oversize since the only extra weight they will cany is the dead weight of the jack trusses themselves. Simple as this system is, many builders still prefer to frame these roof intersections as a farmers valley (see 137) with solid-sawn lumber.
Rectangular openings for skylights or chimneys may be constructed in a truss roof. Small openings less than one truss space wide may be simply framed between trusses as they would be in a rafter-framed roof (see 135-136). Openings up to three truss spaces wide are made by doubling the trusses to either side of
the opening and attaching header and mono or other special trusses to the doubled trusses. Larger openings (more than three truss spaces wide) require specially engineered trusses in place of the doubled trusses. Obviously, it is most efficient if the width and placement of the opening correspond to truss spacing.
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