Why Do IBR Roofs Leak? Laps, Screws, Rust and How to Fix Them
IBR sheeting is one of the most common roof coverings in South Africa, on homes, carports, workshops, warehouses and factories. It is strong, light and quick to install, but as it ages it develops leaks in very predictable places. Knowing where to look makes the difference between a repair that lasts and one that has to be redone after the next storm.
This article is part of our complete guide to roof waterproofing and our commercial and industrial roof guide.
What Is an IBR Roof?
IBR stands for Inverted Box Rib, the trapezoidal profile of the sheeting: tall, square-ish ribs with wide flat pans in between. Water runs down the pans, while the sheets are fixed with screws through the ribs and overlap one another along the sides and, on long roofs, at the ends. Every one of those fixings and overlaps is a potential leak point.
The Most Common Reasons IBR Roofs Leak
1. Perished screw washers
Each roofing screw has a rubber or neoprene washer that seals the hole. After years of sun, those washers harden, crack and shrink, and water runs down the screw shank into the building. On an older roof, this is usually the single biggest cause of small, scattered leaks.
2. Over- or under-tightened screws
A screw driven too hard crushes the washer and dents the sheet, leaving a hollow where water collects. One left too loose never sealed in the first place. Both cause leaks, sometimes from the day the roof was installed.
3. Side laps
Where two sheets overlap along a rib, wind-driven rain can be pushed sideways into the lap. On lower-pitched roofs, water can also be drawn into the overlap by capillary action. Side lap leaks often show up as a line of drips along the same position in the ceiling.
4. End laps on long roofs
Where a roof is too long for single sheets, the sheets overlap end to end. If that overlap is too short, or the pitch is low, water backs up under the upper sheet during heavy rain.
5. Rust at cut edges, laps and swarf marks
Rust starts where the protective coating is broken: cut edges, scratches, and especially the tiny hot metal filings (swarf) left on the roof when holes are drilled. Swarf rusts within weeks and leaves pitting behind. Laps also trap moisture, so rust often starts inside the overlap where you cannot see it.
6. Flashings, ridges and penetrations
Ridge caps, wall flashings, valley gutters and anything that passes through the roof, such as vent pipes, skylights and solar mounting brackets, all need their own seal. When those seals fail, water gets in at the joint rather than through the sheet.
7. It might not be a leak: condensation
On cold mornings, warm, moist air inside a building condenses on the underside of uninsulated IBR sheeting and drips. It looks like a leak, but it happens on dry days too. If drips appear without rain, condensation is the likely cause, and the fix is insulation or ventilation rather than waterproofing.
Signs to Look Out For
- Drips or stains in a regular pattern, often matching screw lines or laps
- Rust streaks running down from screws or along overlaps
- Daylight visible through fixing holes from inside
- Old sealant or bitumen patches along the laps that have cracked or lifted
- Loose or missing screws, especially at the edges and ridge after strong wind
How to Fix a Leaking IBR Roof
Spot repairs
Replacing perished screws and washers, sealing individual laps and patching rust spots can stop specific leaks. The problem is that on an ageing roof every other screw and lap is the same age and will start leaking soon after. Spot repairs are fine for a young roof with one problem, less so for an old roof with many.
Seal the whole roof with a liquid membrane
On a roof where the sheeting is still structurally sound, a fully bonded liquid-applied membrane treats every screw, lap, flashing and rust spot at once. The roof is cleaned, rust is treated, loose fixings are secured, details are sealed by brush, and the membrane is applied over the whole surface. It cures into one continuous, elastic layer that moves with the metal as it heats and cools, which is something rigid patches and sealant strips cannot do.
Replace the sheets that are beyond saving
Sheets that are rusted through, holed or structurally weak have to be replaced first. On most roofs that is a handful of sheets, not the whole roof.
How EcoProof Africa Handles IBR Roofs
We inspect the roof from above and, where possible, from below, to separate real leaks from condensation and to identify any sheets that must be replaced. On sound roofs we seal the whole surface with a seamless, fully bonded liquid system that needs no fleeces or primers. On larger commercial and industrial roofs the spray grade covers up to 800 m² a day, and work can usually continue in the building underneath. See metal roof waterproofing and industrial roof waterproofing for more.
Where to Go From Here
- How Do I Know If My Roof Needs Waterproofing? Seven warning signs.
- Why Do Box Gutters Leak? The other common leak on metal roofs.
- When Is the Best Time to Waterproof Your Roof? Planning work around the rainy season.
If your IBR roof is leaking, get in touch to arrange an inspection.
Frequently Asked Questions
Why does my IBR roof leak at the screws?
Usually because the rubber washers have perished in the sun, or the screws were over- or under-tightened when the roof was installed. Water then runs down the screw shank into the building.
Can I just replace the screws?
On a young roof with a few failed fixings, yes. On an older roof, the laps, flashings and remaining screws are usually the same age and will start leaking soon after, so sealing the whole roof is often better value.
My roof drips on dry mornings. Is that a leak?
Probably not. Drips on dry, cold mornings are usually condensation forming on the underside of the sheeting. Insulation or better ventilation solves it, not waterproofing.
Can a rusty IBR roof be waterproofed?
Yes, if the sheets are still structurally sound. Surface rust is treated before the membrane goes on. Sheets that are rusted through must be replaced first.
Is waterproofing cheaper than replacing an IBR roof?
In most cases, yes. If the structure and most of the sheets are sound, sealing the roof avoids the cost of new sheeting, removal and the disruption of a full re-roof.
Our roof waterproofing services
EcoProof Africa waterproofs flat roofs, metal roofs, corrugated roofs and asbestos roofs, and can help with gutters and concrete slabs. See all our waterproofing services. We work across Gauteng, including Johannesburg, Randburg, Sandton, Edenvale, Germiston, Boksburg, Benoni, Brakpan, Springs, Bedfordview.