A cedar roof signals replacement when it passes its 20-to-40-year shake or 30-to-50-year shingle service life, when cupping spreads across the field, when splitting crosses 25 to 30% of the roof, or when the deck rots, per the Cedar Shake & Shingle Bureau and InterNACHI.
Each of these signs marks moisture-driven failure that has moved past spot repair toward a full cedar tear-off and replacement.
When Does a Cedar Roof Reach the End of Its Service Life?
A cedar roof at or past its service life signals replacement, because cedar shake lasts 20 to 40 years and cedar shingle 30 to 50 years, per the Cedar Shake & Shingle Bureau. The InterNACHI life-expectancy chart lists wood at 25 years, and maintenance sets where in that range a cedar roof lands, because moisture cycling drives most premature cedar failure, per Cedar Shake & Shingle Bureau and NRCA guidance.
Newark's freeze-thaw load shortens a cedar roof's reach within that range, because the city crosses the 32 degree F freezing point repeatedly through winter with an average January low near 25.5 degrees F, per NOAA 1991-2020 normals at Newark Liberty (EWR). The repeated freezing and thawing, paired with the moisture a wood roof holds, drives the cupping, splitting, and rot that ends a cedar roof, per Cedar Shake & Shingle Bureau and NRCA maintenance guidance.
What Surface Signs Show a Cedar Roof Has Failed?
Widespread cupping and warping across the cedar field indicates advanced moisture cycling, the dominant cedar failure mode, because moisture-driven cupping and warping degrade a cedar roof faster than insects, per Cedar Shake & Shingle Bureau and NRCA guidance. The cupping marks wood that has cycled through wet and dry too many times to recover.
Edge splitting and cracked shakes across more than 25 to 30% of the roof cross the contractor-consensus area threshold that favors replacement over continued spot repair, per industry repair-vs-replace guidance. Once damage spans that share of the field, patching individual shakes no longer restores the roof.
A shake that cracks under light bending fails the cedar flex test, the InterNACHI sign of advanced degradation regardless of surface appearance, per the InterNACHI flex-test guidance. A shake that snaps rather than flexes has lost the integrity that keeps the wood watertight, even where the surface still looks intact.
Moss and algae buildup with rot beneath cupped shakes indicates trapped moisture, the condition that accelerates on north-facing and shaded slopes where a cedar roof dries slowly, per Cedar Shake & Shingle Bureau guidance. The growth holds water against the wood, feeding the decay that the slow-drying slopes already invite.
Which Deck Conditions Point Past a Patch to Replacement?
A spongy or sagging roof deck under the cedar indicates moisture-rotted sheathing from years of trapped water beneath the wood, a structural condition that points toward replacement rather than a surface patch, per GAF inspection guidance. The softness traces to plywood or OSB that has absorbed water the failing cedar no longer kept out.
Daylight through the roof deck, seen from inside the attic, indicates holes in the decking and the cedar field, a sign that points toward replacement rather than a patch, per This Old House. A full tear-off exposes the deck so the contractor inspects and replaces the rotted plywood or OSB, because N.J.A.C. 5:23-6.4 prohibits roofing over wood shake and over a water-soaked or deteriorated deck.
When a cedar roof passes its service life, cups and splits across more than 25 to 30% of the field, fails the flex test, or rots the deck beneath it, the signs together point past spot repair to a full tear-off and replacement.