Steel Structure Waterproofing: Complete Guide to Fix Leaks & Prevent Damage

1.Longitudinal Lap Joints
These occur when the length of a single roofing sheet is insufficient, requiring overlapping joints.
Solution: Cover the joints with a 25 cm wide OFAN waterproofing system. For old roofs, remove the existing waterproofing layer first.

2.Transverse Lap Joints
Common in old roof panel types and new panels with poor edge locking.
Solution: Cover with a 10 cm wide waterproofing layer.

3.Roof Screws and Fasteners
A widespread issue, especially on double-layer or single-layer color steel roofs. Improper screw driving (too tight, too loose, angled, or misaligned) can deform or dislodge the rubber gasket or create depressions, leading to dripping water that accumulates in insulation layers. Misaligned screws that miss the purlin also create holes. On single-layer roofs without insulation, leaks may be less noticeable as water disperses along the steel panel and purlin contact points before dripping.
Solution: Cover each screw with a 10 cm × 10 cm waterproof layer.

4.Roots of Roof Equipment (e.g., Fans, Exhaust Vents, Louvers)
Ensure proper drainage around these areas; if water pools, modify the roof panel first. Many installers add flashing (water baffles), but poor design can trap water for long periods, accelerating corrosion. We recommend trimming the raised roof panel corrugations within 20 cm of the equipment’s windward side to improve drainage.

5.Pipe Penetrations Through the Roof
The OFAN waterproofing system is ideal for complex pipe openings of various sizes. Large pipe boots with rubber caps create three potential leak points (top, bottom, and side seals). OFAN is applied in liquid form, curing into a seamless, flexible membrane that bonds tightly to both pipe and roof panel.

6.Ridge Leakage

6.1 Ridge Area
Causes: High corrugation peaks preventing ridge cap sealing; no waterproofing at longitudinal overlaps; rivets used for lap joints weakening from thermal expansion/contraction; missing or improperly placed foam closures.

6.2 Monitor (Sawtooth) Roof Area
Causes: No foam closure under the transition flashing; missing longitudinal waterproofing at flashing laps; roof outer panel not extended under the monitor; unsealed openings around monitor support columns; inherent manufacturing/installation defects.

6.3 Skylight / Daylighting Panel Area
Causes: Poorly applied sealing compound or leaking screws; profile mismatch between skylight and roof panel (skylight corrugation higher than roof panel, creating pressure differences and capillary water ingress); insufficient longitudinal lap length with aged sealant; missing sealant; rigid contact between skylight and steel panel leaving gaps.

6.4 Roof Openings (e.g., Fans)
Causes: Improper waterproofing detail at fan openings; unsealed steel closures; insufficient clearance around openings hindering water flow; poor flashing laps at openings; no structural supports causing ponding; waterproofing that creates water retention.

6.5 Eaves Area
Causes: Missing foam closures at panel ends; roof panels not bent downward; insufficient wall panel length; missing waterproof flashing at eaves.

6.6 Gutter Area
Causes: Gaps in welded internal gutter joints; undersized gutter or downpipe relative to roof slope/length; missing gutter end cap; roof panels extending too short into the gutter, causing backflow.

6.7 Canopy Area
Causes: Improper connection between canopy and attached building; missing closures between canopy and exterior wall, or failure to insert into wall panel as designed.

6.8 Interface Between Main Building and Attached Building
Causes: Improper construction; transition flashing not meeting design requirements.

6.9 Brick Wall to Light-Gauge Steel Roof Connection
Prone to leaks due to differential movement causing cracks at the interface.

6.10 Aluminum Windows
Difficult area. Causes: Gaps between wall purlins and window frame; poor sealing at window bottom (with steel/brick wall) and between glass and frame; large gaps or reverse slope at sill; improperly sealed flashing above window.

7.Changes in Roof Height / Interior Wall Base
Caused by improperly installed flashing or horizontal lap joints in these areas.

8.Downspout / Scupper Openings
Causes: Leaks at the joint between downspout and drain pipe; scupper outlet not at the lowest point, leading to standing water (old auxiliary waterproofing degraded); leaks at gutter section welds; insufficient number or small diameter of scuppers, or clogging, causing overflow between gutter and roof panel edges.