A sagging roof is the frame telling you that something is carrying more load than it should, or has lost some of its strength. On Adelaide homes the cause can be as simple as an old strut that was removed during a renovation, or as serious as rot, termite damage or a wall that has moved. This guide explains how to read the sag, what usually causes it, and how to get it fixed in the right order.
First, decide whether it is urgent
Most sags creep in slowly over a long time. Some do not. Treat it as urgent and keep people out of the rooms below if you notice any of these:
- The dip has appeared suddenly or is clearly getting worse week to week
- Ceilings below are bulging, cracking in new lines or drooping
- You hear creaking or cracking from the roof, especially in wind or after rain
- Doors and windows near the sag have started to jam
- There is fresh water damage alongside the sag
In those cases, ring a roofer for a make-safe visit. Our emergency roof replacement page explains what that involves. If none of these apply, you have time to book a proper inspection.
Read the sag by where it sits
The location of the dip is the most useful clue.
| Where the sag shows | What it often means |
|---|---|
| Along the ridge line | Ridge board or strutting has dropped, or walls have spread apart |
| Mid-span between ridge and gutter | Rafters or purlins bending under load, or a removed underpurlin strut |
| Along the eaves or gutter line | Rotten rafter ends or fascia, or the top of a wall moving |
| Local hollow in one area | Rot from a long-term leak, termite damage or a broken member |
| Whole roof plane bowed | Framing too light for the roof covering, often after a re-tile |
These are starting points, not diagnoses. Only a look at the timbers will confirm the cause.
The usual causes on Adelaide houses
Heavy roofing on light framing
Concrete tiles are much heavier than steel. Where an older villa or bungalow originally roofed in corrugated iron was later re-roofed in concrete tiles, the frame may never have been upgraded to carry the extra weight. Over time the rafters and purlins bow. The same can happen where a second layer of material was laid over an old one.
Struts removed or cut
Roof frames rely on struts and braces that carry load down to internal walls. During past renovations, people sometimes removed a strut to fit ductwork, a manhole or storage, or took out an internal wall without propping the roof above. The roof drops slowly afterwards.
Rot from long-term leaks
A slow leak that drips onto the same timber for years softens it until it bends. Valleys, flashings around chimneys and the low edge of the roof near the gutters are common spots. Fixing the leak stops the rot spreading, but softened timber needs replacing.
Termites
Subterranean termites are active across much of Adelaide and are drawn to damp timber. They can hollow out rafters and wall plates while the surface looks intact. If the inspection finds mud tracks or hollow-sounding timber, a pest inspection should happen before any rebuild.
Walls and footings moving
Much of the Adelaide Plains sits on reactive clay that swells in winter and shrinks in summer. That seasonal movement can push walls out of line, which lets the roof spread and the ridge drop. Cracked brickwork, gaps at cornices and sticking doors often show up at the same time. Here the roof is the symptom, and the footings or walls may need attention too.
Storm loading
Severe thunderstorms with hail can load a roof heavily in a short time, and strong winds can shift or loosen framing connections. After a big storm, a new dip is worth reporting promptly, particularly if you plan to make an insurance claim. Our insurance roof replacement page has more on that process.
Sags that are not the frame
Not every dip means the rafters are failing. A gutter that has pulled away from its brackets can make the eaves line look droopy from the street. Battens that have warped or split under one area of tiles can create a shallow hollow while the rafters underneath are straight. On metal roofs, sheets that were fixed to uneven purlins can look wavy without anything having moved. A roofer can usually tell these apart quickly, and they are much simpler to put right than a structural sag.
What you can safely check yourself
From the ground, sight along the ridge and the gutter line from each end of the house. Photograph the roof from the same spot so you can compare over a few weeks.
From the ceiling space, only if access is safe and you can stand on the joists, look for:
- Rafters that are visibly bent or cracked
- Struts that stop short of the roof, or are missing altogether
- Dark, soft or crumbly timber, especially near valleys and the eaves
- Gaps between timbers that should be joined
- Mud tubes or soil-like trails on timber
Do not cut, prop or jack anything yourself. A loaded roof frame can move suddenly.
How it gets fixed
The repair depends on the cause, but the order is nearly always the same.
- Find and stop any water entry. There is no point repairing a frame that will keep getting wet.
- Deal with pests if they are present. Treatment comes before new timber goes in.
- Repair or strengthen the frame. This can mean replacing rotten rafters, adding struts or braces back down to load-bearing walls, sistering new timber alongside bent members, or tying spread walls back together. Larger structural fixes may need a design from a structural engineer.
- Address the roof covering. If the tiles or sheets are sound, they can often be relaid once the frame is straight. If they are worn out, or too heavy for the frame, this is the point to consider re-roofing, often in lighter steel through a metal roof replacement.
A small, local sag caused by one leaking valley can be a modest roof repair. A whole roof bowing under the weight of concrete tiles is a bigger project, and is often the point at which homeowners re-roof.
Approvals and planning
Repairs that keep the same roof shape and materials are often simple from a planning point of view. Structural alterations, a change in roof form, or work on a heritage-listed home or in a heritage area may need development approval through the PlanSA portal under the Planning and Design Code. Check with your council before work starts. Your contractor should also tell you whether an engineer's sign-off is needed.
Choosing who does the work
Sagging roofs sit between trades, so make sure whoever quotes is clear about who will repair the frame and who will handle the covering. We ask the contractors we work with to hold the licences and insurance the job needs, and you should feel free to ask to see them before work starts. Builder licences in South Australia are issued by Consumer and Business Services (CBS), and you can check them on the CBS public register. For a sense of what pushes the price up or down, see our roof replacement cost guide.
When you are ready, contact us and we will connect you with a local roofer to inspect the sag and explain the options.