IDEAL ROOFING SYSTEM

When a flat roof leaks badly every time it rains, patching it is often a waste of money. On a recent job in Ibafo, Ogun State, we fixed severe rainfall leaks on a 15-metre-long commercial building by replacing the whole roof. We stripped the old sheets, replaced the timber the water had spoilt, and installed new Normal Longspan aluminium using the double lapping method. We finished with wall coping and capping, and the job is covered by our one-year leak warranty. This post walks through what we did and why.

The problem

The building is a long, single-storey commercial property with a flat roof, 15 metres from end to end. Every time it rained, water came through in several places. The old sheets were stained and worn, and water had been getting in for long enough to damage the timber underneath.

Rain in this part of the country is not a small matter. NiMet's 2026 Seasonal Climate Prediction expected a longer-than-normal rainy season for Lagos and Ogun States (Federal Ministry of Aviation and Aerospace Development). A roof that leaks in light rain will not survive a long season.

Stripping the old roof

We started by removing the old roofing sheets completely. Stripping the roof lets us see the real condition of the timber, instead of guessing from below, and it means the new sheets sit on a clean, sound frame.

Fixing the damaged wood

Once the old sheets were off, we checked every rafter and purlin. Where the leaks had spoilt the timber, we replaced it before installing anything. New sheets on rotten wood would only move the problem, so this step matters as much as the sheets themselves.

Single vs double lapping, and why we chose double

There are two ways to overlap longspan sheets on a roof like this: single lapping and double lapping. We chose double lapping because the building is very long. On a long, low-pitch flat roof, water moves slowly across the sheets, so every joint has to be as tight as possible. Manufacturer guidance for low-slope aluminium roofing also warns that water can pond on very low slopes, especially where sheets are end-lapped (Lysaght Permalite installation guide). Double lapping gives the joints extra protection against the wind-driven rain that finds its way into weak laps.

Installing the longspan

On this Ibafo job we used Normal Longspan: 0.9 metre wide beige corrugated aluminium roofing sheets. Our crew carried each continuous sheet, about 15 metres long, across the timber frame and locked it into the side lap of the sheet before it. Running one sheet from end to end means no joints across the length of the roof. We cut neat round openings where pipes come through.

Wall coping and capping

Many flat roof leaks do not start on the sheets at all. They start where the roof meets the wall. We did wall coping and wall capping along the walls to close those gaps and stop rainwater getting in at the edges. Building-science guidance on parapets makes the same point: copings and the joints under them are a common source of leaks, so the top of the wall needs proper protection (Building Science Corporation).

Material checks by the client

The client chose 0.7mm aluminium. Before installation, they checked the thickness on site with a caliper and counted the pieces to confirm the quantity they paid for. We encourage every client to do this. Good materials should pass any check, and our materials are certified by the Standards Organisation of Nigeria (SON).

Results and client satisfaction

The building now has a clean, continuous beige roof, sound timber underneath and sealed wall edges. The client was very satisfied with the work and with the materials.

One-year leak warranty

Once the installation is done and the replacement is confirmed, the roof is covered by our one-year warranty against leakage.

Signs you need a roof replacement, not just repair

• The roof leaks in several places, not just one.
• Leaks come back soon after patching.
• The sheets are heavily stained, rusted or worn.
• The timber under the roof is soft, stained or rotten.
• Water gets in where the roof meets the wall.

If you see these signs, get the roof inspected before the next heavy rains.

Frequently asked questions

Where was this roof replacement done?

In Ibafo, Ogun State, on a long single-storey commercial building with a flat roof.

Why did you replace the roof instead of repairing it?

The leaks were severe and had already spoilt some of the timber. Patching would not have stopped the water.

What roofing sheet did you use?

Normal Longspan, 0.9 metre wide beige corrugated aluminium roofing sheets, in 0.7mm thickness chosen by the client.

What is double lapping?

It is one of two ways of overlapping longspan sheets, single and double lapping. We used double lapping because the building is very long and has a low-pitch flat roof.

Do you give a warranty on roof replacement?

Yes. Once the installation is done and the replacement is confirmed, we give a one-year warranty against leakage.

Do you work outside Lagos?

Yes. This job was in Ibafo, Ogun State, and we deliver nationwide.

Need a roof replacement or an estimate? Message us on WhatsApp on 08059431517, visit our showroom at 83 Dopemu Rd, Orile Agege, Lagos, or see our website. Current prices are on our aluminium roofing sheet price list. See also how to choose an aluminium roofing sheet supplier and, for older roofs that are still sound, roof repainting in Nigeria.