northern california. rain only, yearly totals are around 10-15 inches per year, rare freezes to 26 F. i have a 1940 ranch house built by a farmer and his uncle! front half is only 2x4 rafter 16’ span, about a 5/12 slope. the rafters have single props, no purlin. its always been wood shingle (1940-1986) or now cedar shake. im wanting to convert to comp shingle, worried about the added weight of re-roofing using osb decking plus shingles. currently the deck is 1x4 spaced 50%. shakes cannot be used in CA.
question: regardless of increased cost, is it viable to deck the roof by adding 1x4 between bats, provided there is a small gap for expansion? the existing 1x4 is in great condition, tho im sure hard as a rock.
alternatively, is the added weight of simply overdecking with osb not a big deal?
is a purlin support system the best answer?
is stripping the 1x4 and replacing with osb only (4 feet at a time) a better option?
when i consider how light the roof is, and how those 2x4 rafters have never bowed, it gets me thinking. back half is engineered truss. side gables have short rafter length.