Since the boards used for shiplap were manufactured here in the pacific northwest it was still cheaper than plywood up through the 1960s.
Re decking roof.
This is usually because low quality leak prone decking materials such as epdm rubber are used often in an effort to save money.
Until the 1940s exterior grade plywood was not available.
On average 300 sq ft.
Is it necessary to space the 7 16 osb on a re deck over a 1x12 lumber deck i think it needs room for expansion and contraction i say yes but a roofing contractor i know tells me it s not necessary re decking a roof general discussion contractor talk.
Roof decks on homes built before 1970 are often 1 8 fir pre plywood shiplap.