Reading the roofline
Stand across the street and look at your roof. The ridge should be a straight line. The roof planes should look flat, not dished. Gutters should run evenly along the fascia. If you see a dip in the ridge, a hollow in the middle of a slope, or waves along the eaves, the frame underneath has moved.
Some sags are cosmetic and decades old. Others are a sign that timbers are failing now. Telling the two apart is a job for a professional, but understanding the causes helps you ask the right questions.
Common causes in Melbourne homes
Heavy tiles on a light frame
Concrete and terracotta tiles are heavy. In some post-war houses and later renovations, roofs were tiled over frames designed for lighter coverings, or extensions were added with undersized rafters. Over years, timber creeps under sustained load and the roof settles into a sag.
Failed purlins, struts and underpurlins
Traditional pitched roofs rely on purlins running along the slope, supported by struts down to internal walls. If a strut has been removed, perhaps to fit ducting, a hot water service or a ceiling fan, or if a supporting wall was taken out during a renovation, the purlin can bow and the roof plane above it sinks.
Rot from long-term leaks
Water getting in for years softens rafters, battens and wall plates. Leaking valleys and box gutters on older terraces are common culprits, as are blocked gutters overflowing into eaves. Rotten timber loses strength and deflects. Read leaking roof replacement for how leaks are traced.
Termite damage
Termites are active in many Melbourne suburbs and can hollow out roof timbers without obvious external signs. If a roofer or inspector finds damaged timber, get a pest inspection before deciding on repairs.
Reactive clay and house movement
Much of the western and northern suburbs, and pockets elsewhere, sit on reactive clay that heaves when saturated and drops back when it dries out. With the footings rising and settling, walls rise and fall unevenly and the roof frame twists with them. You may see a dipping ridge alongside cracked brickwork, sticking doors and gaps at cornices.
Storm or impact damage
Fallen branches and extreme winds can crack rafters or push the frame out of shape. This is usually sudden and obvious. See our guide to storm-damaged roof replacement.
Warning signs to take seriously
Not every sag is urgent, but these signs suggest the structure needs prompt attention:
- The sag is new, or noticeably worse than last year.
- Cracks are appearing in plaster ceilings, cornices or internal walls.
- Doors and windows have started sticking or swinging open.
- Ceilings are bowing or have water stains near the dip.
- You hear creaking or cracking in the roof during wind or heat.
- Tiles are cracking or slipping along the line of the sag.
- Timber in the roof space looks split, crushed, wet or eaten.
If you see any of these, keep people away from the affected rooms and arrange a structural assessment.
Is it still moving? Simple ways to monitor
An engineer will make the call, but you can gather useful evidence in the meantime. Take a photo of the ridge from the same spot on the footpath every few weeks, ideally with a fixed reference like a neighbour's roofline or a power pole in frame. Pencil a short line and the date at each end of any internal crack; if the crack grows past the marks, it is active. Note whether doors that stick do so all year or only in wet or dry months, which can point to soil movement rather than roof framing. Bring all of this to the inspection.
Who assesses a structural problem
Structural engineer
A structural engineer inspects the frame, works out why it has moved and specifies the repair: new struts, sistered rafters, replacement purlins, strengthening of beams or reduced roof load. Their written report and drawings give everyone a clear basis for quoting.
Registered building surveyor
Structural repairs, re-framing and changes to roof loads usually involve permit questions under Victoria's Building Act 1993 and Building Regulations 2018. A registered building surveyor, either private or at council, decides whether a building permit is needed and inspects the work. See Melbourne roof replacement building codes and permits.
Roofer and carpenter
Once the engineering is clear, a roofer handles the covering and a carpenter or builder handles framing. On many re-roofs the same crew or contractor coordinates both.
Typical fixes
| Problem found | Common solution |
|---|---|
| Missing or removed struts | Install new struts to a load-bearing wall per engineer's design |
| Bowed purlin | Prop, straighten or replace purlin, add support |
| Undersized rafters | Sister new rafters alongside existing ones |
| Rotten timbers from leaks | Cut out and replace affected sections, fix the leak |
| Frame overloaded by heavy tiles | Strengthen frame, or replace tiles with lighter metal roofing |
| Movement from reactive soils | Address drainage and footings; roof repair may follow |
Where the covering itself is due for replacement anyway, it often makes sense to strip it, fix the frame while it is exposed and then re-roof. Many Melbourne owners in this situation switch from concrete tiles to Colorbond steel, which takes a large amount of weight off the frame. See our metal roof replacement page.
Heritage and older homes
Victorian and Edwardian terraces and Californian bungalows often have original hardwood frames that have stood well for a century but have been altered over time. Removing chimneys, cutting in skylights or adding rooms in the roof can all shift loads. Where the property falls under a Heritage Overlay, as many in the City of Yarra are, changes to the roof's appearance may need planning approval as well as building approval.
Safety notes
Never climb onto a sagging roof. Timbers may be weaker than they look, and tiles can break underfoot. Stay out of the roof space if the ceiling joists look damaged. If you suspect asbestos in ceilings or eaves, leave it alone. Bigger jobs, beyond 10 square metres of non-friable sheeting, are reserved for licensed removalists by WorkSafe Victoria.
Planning and budgeting
Structural work adds to the cost of a re-roof, and it is hard to price until an engineer has specified the fix. Ask for quotes that separate structural repairs from roofing so you can compare like with like. Our roof replacement cost guide outlines the main cost drivers.
For a first opinion, Roof Repair Melbourne VIC can have an independent local roofer inspect and quote free of charge, and they can tell you if an engineer needs to be involved before anything else happens. Check that they hold appropriate registration and insurance before work starts. Reach us via the contact page.