Sagging Roof

A dip in the roof line — reading the difference between character and trouble.

Stand across the road and sight along the ridge: a roof line should read straight. A gentle, even dip on a century-old house is often just the building's age showing — timber creeps under load over decades, and plenty of Victorian ridges have carried a graceful sag for longer than we've been alive. But a sag is still the structure telling you something, and some versions of the message are urgent.

The causes, roughly benign to serious: age-creep in old, adequate timbers — slow, even, stable. Historic re-covering in heavier materials — a roof framed for slate later given concrete tiles carries perhaps double the design weight, and dips to say so. Undersized or altered timbers — purlins propped away, struts removed during loft "improvements". Rafter spread — the feet pushing outward at the eaves, which pairs a dipping ridge with a bulging top of wall and deserves prompt attention. And localised rot — a long-running leak softening one truss or plate, showing as a sharp kink rather than a curve.

Severity reads in the pattern: even and historic is usually stable; new, worsening, sharp, or paired with cracked ceilings and doors that have started sticking upstairs is structural and current.

Features

What's included

Ridge and slope lines sighted and photographed
Loft-side timber inspection — the honest evidence
Covering weight checked against the original framing
Spread indicators checked at eaves and wall heads
Plain-English severity verdict, not alarmism

Repair options

Repair or replace

Matched to cause: stable age-creep gets monitoring and honesty — not every old roof needs "correcting", and jacking a stable historic sag straight can do more harm than leaving it. Overload and undersized timbers get strengthening — additional purlins, struts and bolted sisters alongside the originals, done from the loft. Rot gets its leak found and fixed first, then the affected timber repaired. Genuine structural spread brings a structural engineer into the conversation — we'll say so plainly rather than improvise. And if the sag traces to heavy tiles on slate-era framing, the long-term fix rolls into the re-roofing decision: the right moment to return the roof to a weight it was built for.

Common questions

Frequently asked

Our surveyor noted "roof spread" — how worried should we be? +

It warrants proper assessment, not panic. Spread means the rafters are pushing their supporting walls outward — the follow-up questions are whether it's historic and arrested (common: an old repair already restrained it) or active. Loft inspection plus a look at the wall heads answers that; active spread is fixable with ties and strengthening, and far cheaper caught early.

The roof sagged after it was re-tiled years ago — connected? +

Very likely, if the new tiles were heavier than the originals — the classic case is concrete tile replacing slate, roughly doubling the load on framing sized for the lighter covering. The sag is the timbers' honest response. Strengthening from within the loft usually resolves it without touching the covering.

Can a sagging roof just be left? +

Sometimes, legitimately — a stable, historic, even sag on sound timbers is character, and we'll tell you so in writing if that's what we find. The discipline is baselining it: photographs and measurements now, compared in a couple of years. "Stable" is a finding, not a guess, and the comparison costs almost nothing.