The signs you need cedar shake roofing are a roof at or past its 20-to-40-year life, shakes cupped, curled, or split, a shake that cracks under the flex test, deep moss or lichen, or deck decay across 15% (Cedar Shake and Shingle Bureau / InterNACHI / This Old House).
Each of those signs traces back to one root cause on a cedar roof: moisture management, not the cedar itself, sets the lifespan.
When Has a Cedar Roof Reached End-of-Life?
A cedar shake roof reaches end-of-life at 20 to 40 years, per the Cedar Shake and Shingle Bureau, against the single "Wood" service life of 25 years on the InterNACHI life-expectancy chart. Moisture management rather than the cedar itself sets the lifespan.
A cedar shake roof at or past that 20-to-40-year window signals replacement, since the Cedar Shake and Shingle Bureau rates cedar shake at 20 to 40 years while the InterNACHI life-expectancy chart lists all wood roofing, cedar shakes and shingles together, at a 25-year service life. A roof reading inside that range with widespread surface degradation has carried its rain-shedding work to the end of the assembly's drying capacity.
The flex test confirms cedar age regardless of surface look: a shake that cracks under light bending fails the InterNACHI indicator of advanced cedar degradation, per InterNACHI roof inspection guidance. A shake that still flexes without cracking holds usable service life, so the flex test, not the calendar alone, distinguishes a tired-looking roof from a structurally spent one.
What Surface and Moisture Signs Appear?
Cupped, curled, and split shakes mark moisture-cycling degradation, the dominant cedar failure mode, per Cedar Shake and Shingle Bureau guidance, as repeated wetting and drying works the wood against its grain until the shakes distort and fracture across the field.
Deep moss and lichen growth prying the shake edges apart retains moisture against the wood and accelerates rot, the moisture-driven decay that causes most premature cedar shake failure, per Cedar Shake and Shingle Bureau guidance. Moisture, not insects, drives most cedar failure, and a cedar shake roof needs at least 1.5 inches of underside air space for drying, so north-facing and shaded slopes that dry slowly degrade faster than sun-exposed ones.
Brown or yellow ceiling and wall stains that spread after rainfall indicate an active roof leak or trapped attic moisture beneath the cedar field, per GAF and This Old House inspection guidance. A spreading interior stain points to water finding a path through a failed shake, a flashing detail, or an under-ventilated attic, and it warrants an inspection of the cedar field and the deck below it.
When Does Area or Deck Decay Favor Replacement?
Cupping or splitting across more than 25 to 30% of the shakes favors full replacement over selective shake repair, per Cedar Shake and Shingle Bureau and industry guidance, because widespread moisture-cycling damage outpaces a tile-by-tile repair approach.
Deck or sheathing decay beneath cupped shakes across more than 15% of the roof area crosses the structural threshold that favors replacement, per industry repair-versus-replace guidance, since rotted sheathing under the cedar field cannot be corrected by swapping shakes on the surface. A cedar shake replacement strips the existing covering to the deck, because the NJ Rehabilitation Subcode requires complete removal of a wood-shake, slate, or tile covering rather than a recover-over, per N.J.A.C. 5:23-6.4.
Untreated cedar shakes carry no fire classification under UL 790 and ASTM E108, while pressure-impregnated fire-retardant cedar shakes reach a Class B or Class C rating, per the Cedar Shake and Shingle Bureau Certi-Guard program, so a replacement is the point to address fire rating where occupancy rules apply. A cedar re-roof on a detached one- and two-family home counts as ordinary maintenance under N.J.A.C. 5:23-2.7 and needs no construction permit, though a structural change to rafters or trusses still triggers one; compare the broader system on the cedar shake roofing service page.
A cedar roof signals replacement when it reaches its 20-to-40-year life, when shakes cup, curl, split, or crack under the flex test, when moss and lichen pry the edges, or when deck decay spreads beyond 15% of the area, and moisture management is the thread running through every one of those signs.