A roof with shingles laid over a wavy, uneven deck will:

Asphalt shingles are flexible and thin, and they conform to whatever they are fastened to rather than correcting it. A wavy deck therefore shows through as visible undulation across the finished roof — the telegraphing this question names — and the consequences go beyond appearance. High spots take concentrated foot traffic and weather exposure and lose granules faster; low spots hold water longer after rain and collect debris, extending the time the surface stays wet. Fasteners at a hump may not seat flat, and the shingle can lift slightly at the crown of each wave, which is where wind gets underneath. The underlying deck problem — sagging sheathing between rafters, delamination, or rafter deflection — is itself worth investigating, because it points to either undersized framing or a past moisture problem.

Shingles conform to the deck rather than flattening it, so an uneven deck telegraphs through the finished surface. High spots wear faster while low areas hold water and debris, producing uneven deterioration across the roof.

Roof covering performance depends on the substrate. Sheathing that sags between rafters, has delaminated, or sits over deflected framing produces an uneven surface that shortens covering life and can indicate framing or moisture problems beneath.

Shingles Follow, They Do Not Fix. Every wave in the deck shows up on the roof, and every low spot holds water a little longer.

Report the deck condition as well as the covering. An uneven deck may indicate undersized sheathing, missing clips or past moisture damage, and that is the more consequential finding.

• •Expecting the covering to correct substrate irregularity
• •Treating telegraphing as purely cosmetic
• •Reporting the shingles without investigating why the deck is uneven