Johnson-level-tool-mfg RAS-1 Manual do Utilizador descarregar pdf (Página 24)

JACK RAFTERS

JACK RAFTER LENGTH: The Jack Rafter Tables are dier-

ent than those for the other rafters. The table lists, in the

ﬁrst column, the varying center-to-center spacing of the

jack rafters. Then in the second column is the dierence in

lengthfromonejacktothenext(seeFigures14and15).

This dierence in length is to be added to or subtracted

from the rafter length as you progress from jack to jack

(usingthespacingselected).Inourexampleofa8"rise,

andletsassumea24"spacing;wehavea2'4-7/8"dier-

ence in length. Therefore, to obtain the length of the ﬁrst

or longest jack rafter, measure the distance from the edge

FIG. 13 Valley Rafter

Layout.

1 2 ... 19 20 21 22 23 24 25 26 27 28 29 ... 66 67

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