They are installed on top of the roof rafters with a felt underlayment or vapor barrier installed on top.
How close purlins for metal roof.
The purlins of a roof support the weight of the roof deck.
Purlins are non pressure treated 1 x 4 x 12 lumber that is installed on to the roof in a specific layout pattern and screw pattern.
Metal roof purlins are installed horizontally under metal roofs.
They are most commonly used in metal buildings though they sometimes replace closely spaced rafters in wood frame structures.
Engineered purlin metal mart offers a complete line of engineered purlin material.
The roof deck is the wood panel ply board or metal sheeting that creates the surface of the roof.
Purlins are 2 by 4 feet and are installed much like metal roofing.
The top chords of some of the trusses seem to be slightly bowed because if i lay a straightedge from peak to eave along some of those lines one or more of the purlins is up to 1 2 higher than the others.
Available in cee or zee shape red oxide primed or galvanized 16 14 or 12 gauge sizes from 4 up to 12 flange widths of 1 1 2 up to 4 cut to your specified lengths hole punching available load tables available for all material.
Metal roofing roof panels the home depot store finder.
The better option is to install 1x4 purlins creating a 3 4 thick air space.
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Purlins parallel to the eave seem called for as the metal roof panels run perpendicular to the eave.
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They give added support to the roof and also provide a nailing surface for the end panels and drip edge.
See graph below for sizes of galvanized metal purlins.
This provides a path to exit for any leaks thru the metal roof but provides little ventilation beneath the metal roofing.
The roof has a 4 12 pitch and covers a 20 width and 48 length.
Custom sizes and lengths available with a two week lead time.
Metal cee purlins are available in a wide variety of sizes and lengths.