Fire Service Ventilation (7th Edition)-Chapter 4 Numbers

Wooden I beam chords are usually made from 2x4 inch lumber, however, 2x3 inch lumber may also be used. Common spacing for wooden I beams is 2 foot on center. Shingles or shakes are usually nailed to wooden 1x4 inch or 1x6 inch planked sheathing with a spacing of about 1 inch. ................
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