IDEAL ROOFING SYSTEM

Your roof leaks every rainy season because of one or more of four things: a sheet thinner than the one you paid for, a rushed installation, wall edges that were not properly covered, or a roofing sheet that does not suit the roof's design and woodwork. Fix the cause, not the drip, and the leaks stop for good.

If you live in Lagos, you know the routine. The first heavy rain comes, a stain appears on the ceiling, and someone is called to "patch" it. Next season, it is back. Patching a symptom rarely works, so in this post I walk through the causes we see most often at Ideal Roofing System, and what to do about each one. We have been roofing in Lagos since 2009. If you want to see what a full fix looks like, read how we replaced a leaking flat roof in Ibafo first, then come back here for the bigger picture.

Rain is also not a small matter in this part of the country. The Nigerian Meteorological Agency, NiMet, publishes seasonal rainfall predictions and weather alerts, and it is worth checking them before you plan roof work.

1. Substandard aluminium sheets

This is the most common cause. For a flat or hidden (parapet) roof, we recommend 0.55mm aluminium. In practice, many people end up with 0.35mm. Some clients even pay for 0.55mm without knowing it, and are supplied a thinner sheet. A thin sheet dents, bends and opens up at the laps, and that is where the water gets in.

A price that is too good to believe is usually a warning sign. If a quote is far below what everyone else is asking for the same gauge, ask yourself where the difference is coming from. Often it is in the thickness.

How to protect yourself

• Ask for the gauge and the grade (Market or Caliper) in writing, on your quotation and your receipt.
• Measure a few sheets from different parts of the bundle with a caliper or micrometer before they are offloaded. Do not offload if the reading is well below what you paid for.
• Ask whether the materials are certified by the Standards Organisation of Nigeria (SON).
• Count the pieces and the lengths against your receipt.

For the full explanation, read our guide to the best aluminium thickness for a flat roof and our checklist for choosing an aluminium roofing sheet supplier. Current rates are always on our aluminium roofing sheet price list.

2. Improper installation: when the roofer rushes and leaves

A good sheet can still leak if it is installed badly. A roofer who is in a hurry to finish and go will skip the slow, careful parts: tight laps, correct fixing, neat cuts around pipes and a final check of the whole roof. Water finds every one of those shortcuts.

Roofing is slow work when it is done properly. On long flat roofs, for example, we use double lapping, because water moves slowly across the sheets and every joint has to be as tight as possible. We also replace any spoilt timber before the new sheets go on, because new sheets on rotten wood only move the problem. Both are explained in our Ibafo roof replacement post.

What to ask your roofer

• How will the sheets be lapped and fixed, and why?
• Will the timber be checked and any bad pieces replaced first?
• Will you walk the finished roof with me before the final payment?
• Is there a written warranty against leakage? Every roof our own team installs comes with a 1-year warranty against leakage.

3. Wall covering that is not done properly

Many leaks do not start on the sheets at all. They start where the roof meets the wall. On a flat or hidden roof, the top of the parapet wall and the joint where the sheets meet the wall must be properly covered with coping, capping or waterproofing. If it is skipped or done in a hurry, rainwater runs down behind it and into the building.

We treat this as non-negotiable. Our post on flat and hidden roof dos and don'ts explains why waterproofing at the roof-to-wall intersection matters so much. Building-science guidance on parapets makes the same point: the top of the wall and the joints under it are a common source of leaks (see Parapets: Where Roofs Meet Walls from Building Science Corporation). In our guide to thickness, we also advise a parapet of at least 300mm high with proper damp-proof courses.

4. The wrong roofing material for the woodwork and design

This one surprises many people. A roof is a system: the design, the pitch (how steep it is), the woodwork underneath and the sheet on top all have to match. If one of them is wrong, the roof will leak, even if every sheet is the right thickness.

Here is a real example. A client put stone coated Shingle tiles on a roof whose design called for longspan sheets only. It leaked, and the roofing has recently been changed. (We are keeping the client's name private.) Nothing was wrong with the tiles. They were simply the wrong choice for that roof's design and woodwork.

Match the sheet to the pitch and the woodwork. Each type needs something different underneath it:

• Longspan aluminium suits flat, hidden and low-slope roofs. The woodwork needs close purlin spacing so the sheets lap properly, which is why Normal Longspan is our go-to design for flat roofs.
• Stone coated tiles are fixed onto battens on a pitched roof, and need trained installers. We advise against them on flat roofs. We have replaced more than seven flat roofs that were first roofed with stone coated tiles, after homeowners reported persistent leaks.
• Lesso resin tiles need purlin spacing that matches each profile, so we inspect the trusses and purlins first.

Manufacturers also give a minimum roof slope for each profile. You can see an example under "Minimum Roof Slopes" in the Lysaght Permalite installation guide. The practical lesson is simple: choose the sheet before the carpenter builds the frame, not after. Our roof woodwork guide shows what the timber looks like on a real roof.

The types of roofing sheets available

Here is a quick guide, so you can pick the right sheet for your roof.

Normal Longspan

Normal Longspan is corrugated aluminium, 0.9 metres wide, made in long lengths so there are few or no joints across the roof. Its narrower, more numerous gutters carry water away well, which makes it the usual choice for flat roofs and industrial roofs. See aluminium roofing sheets: types and grades.

Other aluminium designs

Aluminium also comes as Steptiles and Metrocopo, which are step-profiled sheets with a cover width of about 0.98 metres. They give a more decorative look while keeping aluminium's resistance to corrosion. Prices for all aluminium designs are on our aluminium price list.

Stone coated tiles

Stone coated tiles are coated steel finished with stone chips. We stock the Bond, Classic, Milano, Shingle, Roman and Romania designs. They suit pitched roofs and need trained installers. Read how to choose a stone coated roofing tile supplier and check the stone coated price list.

Lesso resin tiles

Lesso resin tiles are synthetic resin, so there is no metal to rust. We are the authorised distributor of Lesso in Nigeria, and the tiles come with a 25-year warranty. Learn more about Lesso resin roof tiles in Lagos.

Not sure which one fits your roof? We install all of them, so we have no reason to push one over another. Send us your roof plan and we will tell you honestly what suits it.

A quick checklist before the next rains

• Is your sheet the gauge on your receipt? Measure it.
• Are the laps tight and the fixings in place, with nothing left half-done?
• Is the roof-to-wall joint and the top of the parapet properly covered?
• Does the sheet type match the roof's pitch and woodwork?
• Is the timber underneath dry and sound?
• If the roof is sound but worn and faded, read about roof repainting in Nigeria before you replace it.

Frequently asked questions

Why does my roof only leak when it rains heavily?

Small gaps, loose laps, thin sheets and open wall joints often hold in light rain and fail in heavy, wind-driven rain. The fault was there all along; the storm just shows it.

What thickness of aluminium is best for a flat roof?

We recommend 0.55mm for flat or hidden roofs. Ask for the gauge and grade in writing, and measure a few sheets before offloading.

Can I just patch my leaking roof?

A patch can help for a very small, single leak. If the roof leaks in several places, or the leaks keep coming back, find the cause first. It is often the sheet, the installation, the wall joint or the wrong material for the roof.

Can stone coated tiles be used on a flat roof?

We advise against it. Stone coated tiles need a pitched roof. For flat or hidden roofs, aluminium longspan is the better choice.

Do you give a warranty against leaks?

Yes. Every roof our own team installs has a 1-year warranty against leakage.

Where is Ideal Roofing System located?

At 83 Dopemu Rd, Agege, Lagos. We have been roofing since 2009 and deliver nationwide.

Get your leaking roof checked

Tell us what your roof is doing and we will help you find the cause. Visit us at 83 Dopemu Rd, Agege, Lagos, or WhatsApp 08059431517. We have been roofing in Lagos since 2009.