Roof Sagging

A roofline is designed and framed to be straight, running in a clean plane from the ridge to the eave without dips or waves. Sagging is any visible deviation from that straight line, whether a soft dip in the middle of a slope or a general sway across a broader section.

The cause almost always sits in the structure underneath the shingles rather than in the shingles themselves. Rafters or trusses that were undersized for the roof's span in the first place can slowly bow under the roof's own weight over decades.

A slow leak that has gone unnoticed for years can also soften and weaken the decking or the framing beneath it, and once wet wood loses strength, the roof above it starts to settle into whatever the weakened structure allows.

Multiple layers of old shingles left in place through repeated overlay jobs add real weight to a roof over time, and a structure marginal to begin with can start to sag under that accumulated load even without any water damage at all.

Because the cause is structural, sagging is not something a re-roof alone fixes. Shingling over a sagging deck locks the dip into the new roof and does nothing to address the framing problem underneath it.

For a homeowner, a sagging roofline seen from the street or the driveway calls for a documented structural look before any other roofing work is scheduled.

The framing issue has to be identified and addressed on its own. A new roof laid over an unresolved sag just locks the problem in place.