I. Types of Steel Structure Roofs

As the uppermost load-bearing and external enclosure structure of a building, the roof plays a crucial role in the overall building structure, both in its enclosure function and facade design. It is the most vulnerable part of a lightweight steel structure enclosure system to leaks. Its main function is to resist wind, rain, snow, and solar radiation, and to bear the weight of the roof itself, as well as the loads from wind, snow, and people on the roof.

[1] Lightweight steel structure roofs can be categorized into various types based on the materials used, including colored profiled steel sheets, colored steel sandwich panels, colorful asphalt shingles, various lightweight roof panels, GRC panels, metal arched corrugated roofs, and composite profiled steel sheets.

[2] The main materials used for lightweight steel structure roofs and walls are colored profiled sheets or sandwich panels. The connection of colored profiled sheets can be achieved through 3600 rolled edge panels, concealed fasteners, or nailed panels. The purlins are lightweight, thin-walled C- or Z-shaped steel purlins, and the roof slope is generally designed to be 1/10 to 1/15.

II. Roof Panel Connections

In steel structure building roof systems, there are two types of connections for the roof panels: longitudinal connections and lateral connections. Longitudinal connections mainly involve overlapping, where the upper slope slab overlaps the lower slope slab. A special waterproof sealant and fixing strip are used at the overlap. Lateral connections currently mainly include the following three methods: lap joint connection, concealed fastener connection, and interlocking concealed fastener connection.

III. Analysis of Leakage Causes and Solutions for Different Locations

Leaks in the roof maintenance system can be categorized by location as follows:

Ridge Area

★ Causes of Leakage: The ridge crest is too high, making the ridge cap inadequate for waterproofing; lack of sealant or silicone at longitudinal overlaps creates gaps and leaks; the ridge caps are connected with rivets for longitudinal overlaps, which break due to insufficient thermal expansion and contraction, causing leaks; no end caps are installed between the ridge cap and the roof panel, or the end caps are improperly placed and fall off, causing leaks.

★ Solutions: Widen the ridge cap and increase the slope; apply sealant or silicone at the overlaps; replace the seam studs; ensure the end caps match the panel type, and apply sealant or silicone above and below the end caps during installation.

Roof Ventilation Unit

★ Causes of Leakage: Foam plugs were not placed under the edging at the junction of the ventilator and the roof; no sealant or silicone was applied to the longitudinal overlap of the edging; the roof slab was not installed at the junction of the ventilator; waterproofing was not applied to the openings in the ventilator structural supports; the ventilator itself had inherent leakage risks during fabrication and installation.

★ Solutions: Foam plugs should be applied before edging installation; sealant or plugs must be used for longitudinal overlaps and secured with stitching nails; the roof slab must be installed before the ventilator; the ventilator contractor must be required to waterproof the openings after the ventilator structure is completed; the installation quality and waterproofing performance of the ventilator should be inspected.

Skylight Panel Area

★ Causes of Leakage: The skylight panel shape does not match the roof panel shape; the crests on both sides of the skylight panel are higher than the roof panel. After installation, excessive sealing creates a pressure difference between the inside and outside of the skylight panel, allowing capillary water to seep into the roof through the gaps on both sides of the skylight panel; the longitudinal overlap length of the skylight panel is insufficient, and the adhesive has aged and lost its adhesion; the longitudinal adhesive has fallen off; the skylight panel and the color steel plate are rigidly overlapped, and the gap in the middle is not sealed.

★ Solutions: Install waterproof screws on the upper part of the crests; the edge trim at the skylight panel should be firmly sealed to the skylight panel; the longitudinal adhesive on both sides should be widened and laid on the upper part of the crests to prevent capillary water seepage.

Roof Openings

★ Causes of Leakage: Openings were not waterproofed according to design specifications; steel plugs were not fitted with waterproof sealant and silicone; the clearance around the opening was too small, hindering rainwater flow and causing water accumulation; the overlapping edges around the opening were not waterproofed; no structural components were added around the opening, creating a low-lying area for water accumulation; waterproofing construction obstructed water flow, leading to water accumulation.

★ Solutions: Construct according to design drawings and strictly adhere to construction procedures, applying sealant and silicone; the clearance around the opening must meet drainage requirements; waterproofing must be applied immediately after openings in walls and roofs; for subsequent additions to enclosures, purlins or angle steel structures should be added to reduce enclosure deformation; waterproofing installation must be tight and level to ensure smooth water flow.

Eaves Area

★ Causes of Leakage: The eaves area is a major source of leakage. Roof panels were not fitted with foam plugs; roof panels were not properly lowered; wall panels were not long enough; and waterproof edging was not added to the eaves area.

★ Solutions: Foam plugs should be placed simultaneously during the installation of the roof exterior panels, and the roof exterior panels should be tilted down at a 30-degree angle; additional edge trim should be added at the eaves as per design requirements.

Gutter Area

★ Causes of Leakage: Gaps exist at the welded joints of the inner gutter, causing seepage; the gutter and rainwater pipe diameters are designed too small and do not match the slope length of the factory building; end caps are not installed at the ends of the gutter; insufficient extension of the roof exterior panels into the gutter allows water to flow back into the factory building.

★ Solutions: Appropriately increase the depth of the gutter to ensure that rainwater does not exceed the overlap joints.

Brick Wall and Light Steel Roof Connection Area

★ Causes of Leakage: This area is prone to leakage. Leakage at the junction of the roof panel and the cement wall is mainly caused by uneven stress leading to cracking of the silicone sealant and the bonding surface.

★ Solutions: Prevent temperature deformation by using double edge trim connection; when connecting to the brick wall, the edge trim should have a certain angle and be completely sealed; sealant should be pre-applied between the edge trims.

IV. Analysis of Other Causes of Leakage in the Maintenance System

Design Reasons

① The roof rainwater system lacks overflow measures as per specifications. When the intensity of heavy rainfall exceeds the system's drainage capacity, the water will overflow the lap joints and even overflow onto the roof, causing accidents.

② Insufficient number of downpipes leads to long and prolonged rainwater flow along the gutters, causing backlog. The lack of L-shaped edge trim on the upper part of the exterior wall panels creates a potential leak on the inner side of the gutters.

③ The design of the color steel flashing fittings is unreasonable and fails to achieve the desired waterproofing effect.

④ The specifications stipulate component deformation control values: purlin deflection L/180, roof beam deflection L/180 (where L is the span of the bending member). The roof purlin cross-section is too small and the spacing is too large, resulting in excessive deformation of the purlins and profiled sheets under wind loads.

⑤ The effects of structural deformation, temperature difference deformation, drying shrinkage deformation, and vibration were not fully considered, and the waterproofing design does not meet the needs of the base layer deformation.

⑥ The roof slope of portal frame lightweight houses should ideally be 1/8 to 1/20, with the larger value preferred in areas with high rainfall. In southern regions, the roof slope should not be less than 5%. In actual engineering designs, many projects have roof slopes that are too shallow, preventing rainwater from draining into the gutters in a timely manner.

Inappropriate Material Selection

① Plastic pipes are used for rainwater pipes, which have poor strength and are easily damaged during installation and operation of steel structure buildings.

② The steel plates used for gutters are too thin, making weld seams prone to problems.

③ The appropriate type of skylight panels and roofing panels were not selected based on the roof slope; the corrugations are too small, and the lateral overlaps are too few, which is detrimental to drainage.

④ The color-coated panels for the enclosure are too thin; after a period of use, the outer panels corrode or deform due to temperature changes, increasing the gaps between the panels.

⑤ Poor quality galvanized layer on the profiled sheet substrate, with an excessively thin coating, results in a short service life and susceptibility to rust and damage.

⑥ Poor quality self-tapping screw washers are prone to cracking, and the glass sealant ages easily.

⑦ Significant deformation of the panels, with differences in height and spacing between adjacent panels; waterproof rivets should be used for the panel fasteners.

Structural Measures

① End caps are effective in preventing leaks caused by seams and should not be overlooked. Ensure that end caps are properly installed between the color steel sheet and the ridge cap, apply silicone sealant to the lower part of the end cap between the skylight panel and the ridge cap, and install steel end caps at the crests of the color steel sheet at roof openings.

② Gaps are easily widened by temperature changes during overlap; sufficient overlap length should be allowed.

③ Drainage should be facilitated rather than blocked. Generally, sealant should be applied to the inside of the steel sheet during installation; the more, the better.

④ The adverse effects of thermal expansion and contraction of the steel structure roof cladding system must be given sufficient attention, and reasonable structural measures must be taken.

During use

① Arbitrary increases in load on the roof purlins lead to roof panel deformation.

② Excessive dirt accumulation in the rain gutters obstructs water flow.

③ Aging of waterproofing adhesive and sealant, coupled with a lack of necessary maintenance during use.

Many factors contribute to leaks in steel structure maintenance systems. To fundamentally solve the problem, careful design is crucial. A reasonable design scheme must be determined, and detailed construction of the flashing at the following points is essential: the waterproofing layer's termination; expansion joints and partition joints; drainage outlets, entrances/exits, and eaves; and the base of parapet walls, equipment installations, pipes, and chimneys. From a construction perspective, a specific waterproofing construction plan for the maintenance system should be developed, with coordination and cooperation among various disciplines. A well-designed system, proper installation, reasonable construction, correct use, and follow-up service are all necessary to ensure a leak-proof steel structure maintenance system. In short, regardless of the installation method, following certain construction techniques and relevant regulations can reduce or prevent leaks.

For more information needed or any inquiry,please feel free to contact Yumisteel team.