The Joint That Decides The Roof
Follow any leaking industrial roof in Dubai down to its first drip and you will usually find an end lap.
The end lap — where two profiled sheets overlap down the slope — is a waterproofing detail that has been fighting physics since the roof was installed. Steel expands in the Gulf day and contracts overnight; over the years the two sheets breathe in and out relative to each other by millimetres at each joint. Factory mastic strips begin rigid; they get stretched rather than compressed at the wrong time of day; they crack. The lap then becomes an open channel that runs directly down into the purlin line.
Most failed "repairs" treat the lap like a static crack: a liquid sealant or roof paint smeared over it. In a movement joint, that is a cosmetic act — the lap opens again within one or two seasons, usually wider. Compare that with the EPDM lap method used on our industrial projects across Jebel Ali, JAFZA and Dubai Industrial City, and you understand why the two approaches are not prices for the same outcome.
The EPDM Lap Method Step By Step
- Expose the jointFailed mastic, dirt and corrosion cleared from the lap; the exact state of the lap is photographed for the record.
- Prep the surfacesBoth sheet faces cleaned and dried; rust treated where present; loose select fasteners replaced with correct washered screws.
- Adhesion testGerman bonding adhesive applied to a test patch and pulled — verified bonding strength before full coverage is committed.
- Premium bonding & membraneCured EPDM bonded across the whole overlap plus a tail margin onto both sheets, so movement is shared across the membrane not concentrated at one bead.
- Water verificationHose test on the sealed lap line where site rules permit; recorded against per-bay sign-off.
- DocumentationScope captured in the warranty file; treated laps included in the 5-year warranty, extendable to 10 years.
Longitudinal Laps, Ridge Details & Related Joints
The same movement problem exists all down the slope: longitudinal sheet laps, ridge caps, and the fold joints around penetrations. These are all sealed with the same EPDM family in the correct cured/uncured form — one system one roofer one warranty, rather than mixed products that age at different rates. Technical background on the material itself: EPDM roof waterproofing in the UAE.
End Lap FAQs
It is the joint where one metal sheet overlaps the next sheet along the slope — typically a 150–200 mm overlap. It is the most leak-prone area of any UAE metal roof because the roof expands and contracts here daily, and any rigid sealant applied at installation eventually opens the overlap.
Factory butyl or mastic strips perish under UAE heat; when the lap opens the seal cracks with it. Our method cleans the lap and bonds cured EPDM over the entire overlap: a rubber joint that stretches when the sheets move and recovers its shape afterwards, instead of a hard bead that cracks.
By sequencing: each bay section is made watertight before adjacent laps are opened. Bay-by-bay staging plus a daily water-tightness sign-off means only a tiny portion of the roof is opened at once, so stock below stays protected.
No lifting. The lap is cleaned as-is; a few select fasteners along the lap may be replaced where holes have widened, then EPDM and adhesive bond over the zone. No structural de-construction involved in a standard lap sealing scope.
A 5-year warranty applies to properly prepared lap work — extendable to 10 years under the annual maintenance contract. In practice, EPDM in Gulf UV exposure outlasts the fasteners below it; the lap is not renewed until the roof itself is nearing sheet replacement.
Completely. Roof paint is a coating: it bridges the joint only while stiff, then cracks the first season the lap opens further. A lap membrane is an elastomer bonded to both sheets — it is mechanically free to move. That is exactly why reputable lap failure specs call for membranes, not coatings.
Move Your Laps Onto EPDM
One survey, one specification, one warranty — across your entire metal roof detail set.
