I. Leakage at Roof Screws and Fasteners
This type of leakage is relatively common and mainly occurs on double-layer color steel sheet roofs as well as single-layer color steel sheet roofs. During construction, if self-tapping screws are driven with excessive or insufficient force, or are driven crookedly or at an angle, the rubber gaskets of the screws may become deformed, dislodged, or form a concave surface. This leads to intermittent dripping leaks on the roof, which then accumulate in the insulation wool, gradually increasing to form multiple leak points. Additionally, improperly positioned self-tapping screws that miss the purlin beneath the color steel sheet and directly create a hole are also a major cause of leakage. This type of leakage may be less noticeable on single-layer color steel sheet roofs without a thermal insulation system, primarily because rainwater seeping through the contact area between the steel sheet and the purlin disperses directly and does not necessarily drip down immediately.
II. Leakage at Color Steel Sheet Laps
At horizontal lap joints and vertical lap joints, leakage occurs at the overlaps of color steel sheets. If the corrugation height of the color steel sheet is too low or if heavy rainfall causes the water volume to exceed the corrugation height, large-area leakage can easily occur. The leak points are often not easy to detect, and once formed, such leaks are difficult to repair. This problem is more common in curved roofs. The main causes are insufficient tightness between the two overlapping sheets and gaps formed by incomplete installation of self-tapping screws.
III. Leakage at the Ridge
In the construction of light steel structure roofs, leakage caused by ridge caps is also a relatively common phenomenon. During the rainy season, especially during heavy rainfall, splashing rainwater can penetrate the gaps at the butt joints of the two color steel sheets beneath the ridge cap, resulting in large-area seepage. The main causes of leakage in this area are: the corrugation peaks at the ridge are too high, preventing the ridge cap from ensuring waterproofing; failure to apply mastic or silicone sealant at the longitudinal laps, creating gaps that allow leakage; the longitudinal laps of the ridge cap being connected with rivets, which can break due to insufficient strength to accommodate thermal expansion and contraction, leading to leakage; and the absence of end plugs between the ridge cap and the roof panels, or the end plugs being improperly placed and falling off, causing leakage.
Solutions: Widen the ridge cap and increase the roof slope appropriately; apply mastic or silicone sealant at the lap joints; replace the stitching nails/use appropriate fasteners; end plugs should match the panel profile and should be installed with mastic or silicone sealant both above and below. To prevent ridge cap leakage during construction, it is advisable to increase the turned-down edge length of the ridge cap, cut it at the corrugation peaks, and apply sealant at the joints.