Water leakage in steel structure factory buildings? We can provide a comprehensive analysis and solution!

With the deepening of reform and opening up and the rapid development of China's economy and modern industry, there is a need to build a number of large-scale industrial plants. Light steel structure plants, with their simple design, light weight, high strength, convenient fabrication and installation, large span, short construction period, and low price, are the first choice for many foreign investors. However, the history of large-scale construction of light steel structure plants in my country is relatively short, and some production technology and construction process issues have not been well resolved. Therefore, some unsatisfactory aspects still exist in the construction and use of these plants. For example, water seepage is a common quality problem in light steel structure plant projects. Based on years of experience participating in steel structure projects, this article analyzes the causes of water seepage in light steel structure plants and discusses some insights on prevention and control for your reference.

1. Steel structure roof type

 

Steel structure roofs, walls, and other enclosure structures generally use color-coated profiled steel sheets, with a thickness typically between 0.3 and 1.0 mm. These sheets are made by rolling pre-coated colored steel sheets (galvanized or aluminum-zinc coated) into shape and then spraying a paint layer onto the surface. For buildings requiring thermal insulation, heat insulation, and sound insulation, double-layer color-coated profiled steel sheets can be used, with insulation materials (such as glass wool, rock wool, or foam) filling the space between them. The filling material can be applied on-site or pre-formed with the steel sheets at a factory (called a color-coated sandwich panel).

As the load-bearing and external envelope of a building's top floor, the roof plays a crucial role in the overall structure's enclosure and facade design, and is the most common source of leaks in lightweight steel structure enclosure systems. Its main functions are to resist wind, rain, snow, and solar radiation, and to bear the roof's own weight, as well as the loads from wind, snow, and people walking on it. Lightweight steel structure roofs come in various types based on the materials used, including colored profiled steel sheets, color-coated sandwich panels, multi-colored asphalt shingles, various lightweight roofing panels, GRC panels, metal arched corrugated roofs, and composite profiled steel sheets. Color-coated profiled sheets or sandwich panels are the primary materials used for lightweight steel structure roofs and walls. Currently, in steel structure factory projects, pre-finished glass wool sandwich panels or colored profiled steel sheets are mainly used for roofing. Commonly used profiled steel sheet specifications include 28 types such as YX173-300-600, YX130-275-550, YX70-200-600, YX38-175-700, and YX21-180-900. Among the above specifications, there are 360° rolled edge plates, concealed fastener plates with overlapping connections, and nailed plates. The purlins are lightweight thin-walled C-shaped or Z-shaped steel purlins. The roof slope design is generally 1/10 to 1/15.

 

2. Roof panel connection

 

Steel structure building roof panels have two types of connections: longitudinal and lateral. 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 have the following three methods:  

 

1) Overlapping connection involves overlapping the edges of the profiled steel sheets and connecting them into a whole using various bolts, rivets, or self-tapping screws. This connection is further divided into two types: with and without a sealing groove. The roof screws are exposed, and the corrugations are relatively low.

 

2) The concealed fastener type fixing bracket is fixed to the roof purlins using flat-head self-tapping screws, and then the profiled roof panel is fastened to the fixing bracket. There are no exposed screws on the roof, but because it is directly connected to the purlins with screws, it is impossible to control the deformation due to thermal expansion and contraction.  

 

3) Interlocking concealed fastener connection: This is a more advanced roof panel connection method. The roof system uses sliding brackets to fix the roof panels, which is beneficial for roof waterproofing and maintaining the integrity of the roof, and can effectively control deformation caused by thermal expansion and contraction. This connection type is available in 180° and 360° versions.

 

3. Analysis of the causes of water leakage

 

The color steel sheet cladding system itself possesses a certain strength and rigidity, and the material generally does not leak. Leaks in the cladding system are mainly caused by improper joint treatment, material quality, the maturity and completeness of the system design, structural construction, and installation techniques, all of which directly affect the waterproofing effect of the cladding system. Due to environmental and temperature changes, color steel sheets shrink and deform. When displacement occurs at the joints and overlaps, ordinary sealing strips or silicone sealant may not displace synchronously with the sheet surface, causing detachment and resulting in leaks in the color steel sheet roof. Different skylight panels exhibit varying degrees of deformation and aging within the same timeframe. For the same rolled-edge panel, the Butler system's waterproofing performance is far superior to that of a similarly designed imitation; even with the same nailed panels, different construction teams will achieve drastically different installation results. The main causes of roof leaks can be summarized as follows.

 

3.1 Design Factors  

 

1) The "Technical Specification for Steel Structures of Portal Frame Lightweight Buildings" (CECS 102:98) stipulates that the roof slope of portal frame lightweight buildings should be between 1/8 and 1/20, with the larger value preferred in areas with heavy rainfall. However, in actual design projects, construction units, to save money or for other reasons, often request that the roof slope be minimized. Design units, on the other hand, often rigidly adhere to the regulations without considering the actual situation. This results in many projects having excessively shallow roof slopes, preventing rainwater from draining into the gutters in a timely manner, leading to water accumulation and roof leaks.  

 

2) Designers' lack of understanding of local rainfall is also a significant factor contributing to excessively gentle roof slopes and small gutter cross-sectional areas.

 

3) Lack of node design, construction unit arbitrarily selects node methods, the height of the parapet wall at the ridge is not high enough, and the position or height of the pipes and ventilation ducts extending from the roof is inappropriate, which makes it difficult to construct the waterproof layer.

 

4) Inappropriate panel selection: For snap-fit ​​and interlocking panels, there are generally no major problems as long as the on-site installation is done properly. However, if panels that are directly connected with self-tapping screws are used, even if the on-site preparation is excellent and the waterproof sealant is applied well, leaks will still occur due to the thermal expansion and contraction of the panels.

 

5) Inadequate design considerations for roof openings. Holes must not be cut arbitrarily on-site during construction, and waterproofing of these openings must be properly ensured.  

 

6) The color-coated panels of the enclosure are too thin. After a period of use, the outer panels are corroded or deformed due to temperature, and the gaps between the panels increase.  

 

7) If the roof rainwater system is not equipped with overflow measures as required by the specifications, when the intensity of the rainwater exceeds the drainage capacity of the rainwater system, it will overflow the lap joints and even flood the roof, causing an accident.  

 

8) Insufficient number of downpipes, rainwater travels a long distance and takes a long time along the gutter, causing water accumulation; L-shaped edge trim is not added to the upper part of the exterior wall panel, and there is a risk of water leakage on the inside of the gutter.

 

9) The design of the color steel flashing accessories is unreasonable and fails to achieve the waterproof effect.  

 

10) The standard specifies the deformation control values ​​for components: purlin deflection L/180 and roof beam deflection L/180 (where L is the span of the bending member). If the roof purlin section is designed too small or the spacing is too large, the purlin and profiled sheet will deform excessively under wind load.  

 

11) The effects of structural deformation, temperature difference deformation, drying shrinkage deformation, vibration, etc. were not fully considered, and the protection measures did not meet the needs of base deformation.

 

3.2 Construction Factors   

 

1) During construction, the roof cladding was not properly protected; people walked on the roof, damaging its flatness and even causing cracks. There was insufficient sealant, incorrect placement of sealant, excessive use of rivets, and no waterproofing treatment.  

 

2) The gutters are not protected against corrosion. Some construction companies only apply anti-rust paint or asphalt paint when protecting the gutters. After a period of use, the gutters become severely corroded.

 

3) Due to the large span of the steel structure factory roof panels, there are overlaps in the roof panels. Although polyurethane sealant and 138900 stitching nails are used to treat the overlaps, it is often difficult to meet the design theoretical standards during installation, resulting in rain leakage.

 

4) The gutter has no horizontal slope, so at least a 0.5% slope should be left during construction.

 

5) Careless construction at key points. The internal corners of parapet walls and other structures were not rounded as required or the roundness was too small; the ends of the roof membrane were not properly sealed; the top galvanized iron sheet was deformed; there were few fixing points and the sealant was not properly applied; the base of pipes extending from the roof was not properly sealed; the leveling layer around the pipes was not higher than the surrounding leveling layer; and the waterproofing layer's flashing height was insufficient. During rain, the venting channels became blocked, and the vents were improperly placed, causing the insulation layer to be submerged for extended periods. Cracks appeared in the rigid roof, and the waterproof sealant at the joints did not adhere properly to the sidewalls of the joints, leading to water seepage.

 

3.3 Structural Factors  

 

1) Arbitrarily increasing the load on the building during use causes deformation of the roof panels. In particular, arbitrarily increasing the load on the roof purlins causes deformation of the purlins, resulting in water accumulation on the roof.  

 

2) The waterproof adhesive and sealant have aged, and there is a lack of necessary maintenance during the application process.  

 

3) The plugs are effective against water leakage caused by wind and should not be ignored. It is necessary to ensure that the plugs are installed properly between the color steel plate and the ridge cover plate. Silicone sealant should be applied to the lower part of the plug between the skylight and the ridge cover plate. Steel plugs should be installed at the crest end of the color steel plate at the roof fan.  

 

4) When overlapping, the gaps are easily affected by temperature and should be widened. Sufficient overlap length should be left.

 

5) Water should be drained rather than blocked. Generally, sealant should be applied to the inside of the steel plate during installation, the more the better.  

 

6) Sufficient attention must be paid to the adverse effects of thermal expansion and contraction of steel structure roofing systems, and reasonable structural measures must be taken.  

 

3.4 Material Factors 

 

1) Rainwater pipes made of plastic have poor strength, and steel structure workshops are easily damaged from installation to operation.

 

2) Because the steel plate gutter is relatively thin, the weld is prone to problems.  

 

3) The appropriate type of skylight panel and roofing panel was not selected according to the roof slope. The crests are too small and the lateral overlaps are too few, which is not conducive to drainage.  

 

4) The color-coated panels of the enclosure are too thin. After a period of use, the outer panels corrode or deform due to temperature, and the gaps between the panels increase.  

 

5) Poor quality of the galvanized layer on the profiled sheet substrate, with an excessively thin coating, results in a short service life for the profiled sheet and makes it prone to rust and damage.

 

6) Poor quality self-tapping screw washers are prone to cracking, and glass sealant is prone to aging.  

 

7) The panels are obviously deformed, and the height and spacing of adjacent panels are different. Waterproof rivets should be used for the panels.

 

4.  Leakage Prevention Measures

 

(1) Designers should strictly follow the specifications and should not arbitrarily reduce the design indicators in order to save costs. Designers should visit the construction site more often and make designs based on the actual situation.  

 

(2) Designers should make detailed and reasonable node details according to the actual situation, and should not blindly apply the nodes on the drawings for convenience. When designing roof purlins, designers should be conservative and should not blindly reduce the height of the purlins in order to save steel. A higher purlin height is beneficial for preventing leaks.

 

(3) The roof panels should be made of a type with good waterproof performance. According to market surveys, the 760 type on-site composite panels, 475 type color steel panels, and 675 type color steel panels have a 360° interlocking angle of at least 180° and almost no leakage. Although these types of panels are more troublesome to install, the performance is good. 

 

(4) When selecting roof waterproofing materials, reliable manufacturers should be selected. Due to the material characteristics of metal roof panels, waterproofing materials suitable for metal roof panels should be selected. For example, butyl rubber waterproof sealing adhesive tape with high bonding strength, good conformability and excellent weather resistance can be used as a matching waterproofing material for metal roof panels.

 

(5) During the installation of the project, on-site management should be strengthened and the quality of the installation team should be improved. It is best if the steel structure manufacturer has its own construction team or technical backbone and management backbone to curb the power of the contractor.

 

5.  Analysis of the causes and solutions for water leakage in various parts

 

Lightweight steel structure roofs typically have a shallow slope, often below 6%. In rainy areas of central and southern China, roof leaks are common, ranging from large-area leaks to drips at the junction of skylights and ridges. The causes of these leaks are mostly due to several factors, including self-tapping screws, overlapping of color steel plates, ridge tiles, pop rivets, deformation of color steel plates caused by people on the roof, and detachment of waterproof sealant from decorative parts such as skylights.  

 

5.1 Leakage at roof screws and fasteners

 

This phenomenon is quite common, mainly occurring in double-layer and single-layer corrugated steel roofs. During construction, excessive or insufficient force applied to the self-tapping screws, or misalignment or angled driving, can cause the rubber washers of the self-tapping screws to deform, detach, or form concave surfaces, resulting in dripping leaks. These leaks can accumulate through the insulation, eventually leading to multiple leaks. Additionally, misaligned self-tapping screws, missing the purlins under the corrugated steel sheet and creating holes directly, are also a significant cause of leaks. This type of leakage may be less noticeable in single-layer corrugated steel roofs without insulation systems, mainly because rainwater seeps through the contact area between the steel sheet and the purlins and disperses directly, rather than dripping quickly.

 

5.2 Leakage at the joints of the color steel plates

 

Leaks at horizontal and vertical lap joints of corrugated steel sheets can easily occur, especially if the corrugated steel sheet is too low or if heavy rainwater covers the corrugated sheet. These leaks are difficult to detect and repair once they appear. This is particularly common on curved roofs. The main causes are loose overlap between the two sheets, insufficient self-tapping screws creating gaps, etc.

 

5.3 Leakage at the roof ridge  

 

Leaks caused by ridge tiles are a common problem in lightweight steel structure roof construction. During the rainy season, especially when rainfall is heavy, splashing rainwater seeps through the gaps at the joints of the two corrugated steel plates under the ridge tiles, causing large-scale leaks. The main causes of this leakage are: the ridge crest is too high, making it impossible for the ridge cap to provide waterproofing; the longitudinal overlaps are not sealed with sealant or silicone, creating gaps that lead to leaks; the longitudinal overlaps of the ridge caps are connected with rivets, which break due to insufficient thermal expansion and contraction; and the ridge caps are not properly sealed with end caps, or the end caps are improperly placed and fall off, causing leaks. Solutions include: making the ridge caps wider and increasing the slope; applying sealant or silicone at the overlaps; replacing the seam studs; ensuring the end caps match the panel type, and applying sealant or silicone above and below the end caps during installation. To prevent ridge tile leaks, it is advisable to increase the length of the ridge tile flanges during construction, cut the edges at the ridge wave areas, and apply sealant to the joints.  

 

5.4 Roof louver section  

 

The main reasons for the leakage in this area are: no foam plugs were placed under the edge trim at the junction of the ventilator and the roof; no sealant or silicone was applied to the longitudinal overlap of the trim; the roof slab was not installed at the junction of the ventilator; the openings in the ventilator structural supports were not waterproofed; and the ventilator itself had inherent leakage risks during fabrication and installation. The solutions are: foam plugs should be applied before edge trim installation; sealant or plugs should be used to secure longitudinal overlaps with stitching nails; the roof slab must be installed before the ventilator is installed; the ventilator construction company should be required to waterproof the openings after the ventilator structure is completed; and the installation quality and waterproofing performance of the ventilator should be inspected.

 

5.5 Skylight Panel Area  

 

Waterproofing the skylight panel area is a crucial part of maintaining the overall waterproofing system. The application of sealant and the use of waterproof screws during skylight panel installation are major potential sources of roof leaks. Other issues include: mismatched skylight panel shapes with roof panels; skylight panel crests higher than roof panels; overly tight sealing after installation; pressure differences between the inside and outside of the skylight panel; capillary water seeping into the roof through gaps in the skylight panel; insufficient longitudinal overlap of the skylight panels; aged and weakened sealant; longitudinal sealant detachment; and a rigid overlap between the skylight panel and the corrugated steel sheet without proper sealing of the gaps. To prevent leaks in roof skylights, the following points should be noted: First, waterproof screws should be driven onto the upper part of the corrugations; second, the edge trim at the skylight should be firmly sealed to the skylight, and the sealant on both longitudinal sides should be widened and laid on the upper part of the corrugations to prevent water seepage due to capillary action; third, the center-to-center distance between the corrugations on both sides should be controlled to match the center-to-center distance of the skylight corrugations. The height or width of the skylight corrugations should not be reduced due to installation problems or inconsistent dimensions, as this could lead to quality issues; fourth, the longitudinal overlap should generally be no less than 300 mm, and the overlap should be firmly sealed with silicone sealant. Flexible tape should be applied to seal the overlapping areas of the skylights.

 

5.6 Roof opening locations

 

When creating openings in a corrugated steel roof, both aesthetics and waterproofing must be considered. The choice should be based on the opening type and the model of the corrugated steel roof panels. The main causes of leakage in this area are: the fan opening was not waterproofed according to the design specifications; the steel plug was not covered with waterproof sealant and silicone; the area around the fan opening was too small, hindering rainwater flow and causing water accumulation; the overlapping edges around the opening were not waterproofed; the interior of the opening lacked structural components, creating low-lying areas for water accumulation; and the waterproofing construction obstructed water flow, leading to water accumulation. The solutions are: construction must be carried out according to the design drawings and strict adherence to the construction procedures; sealant and silicone must be applied; the area around the fan must meet drainage requirements; waterproofing must be applied immediately after openings in the walls and roof; additional enclosure openings should ideally include purlins or angle steel structures to reduce enclosure deformation; and waterproofing installation must be tight and level to ensure smooth water flow.

 

5.7 Eaves area 

 

This area is the main source of leakage, and the main causes are: the roof panels were not fitted with foam plugs during installation, the roof panels were not lowered, the wall panels were not long enough, and the eaves lacked waterproof edging. The solutions are: foam plugs should be placed during roof panel installation, the roof panels should be lowered by 30°, and additional edging should be added at the eaves as per design requirements.

 

5.8 Gutter section  

 

Overlap joints and sealing joints are two key areas prone to leakage. Compared to reinforced concrete roofs, steel structure roofs have shallower gutters and lack continuous waterproofing between the gutters and the roof, making it difficult to prevent leaks when water accumulates in the gutters. The main causes of leakage in these areas are: gaps at the welded joints of the inner gutters, leading to seepage; undersized gutter and rainwater pipe diameters that do not match the building's slope; lack of end caps at the gutter ends; and insufficient extension of the roof panels into the gutter, allowing water to flow back into the building. Solutions include: appropriately increasing the gutter depth to ensure rainwater does not exceed the overlap joints; conducting waterproofing tests after welding the inner gutter joints, requiring secondary welding if leaks are found; determining the design diameter of the gutter and rainwater pipes based on roof drainage calculations; installing end caps at the gutter ends; and ensuring the roof panels are constructed to the designed length.

 

5.9 Awning area  

 

The main reasons for the leakage in this area are: improper treatment of the joint between the awning and the annex; and the absence of a sealing strip between the awning and the exterior wall, or the failure to extend into the exterior wall panel as required by the design. The solutions are: the joint between the awning and the annex must be overlapped and waterproofed; normally, the flashing on the awning should extend into the exterior wall panel. For ease of installation, the flashing can also be placed directly against the exterior wall panel, but a sealing strip must be installed and the gap sealed with silicone.

 

5.10 Interface between the factory building and the annex building

 

The main reason for the leakage in this area is improper construction, with the joint finishing not meeting design requirements. The solution is: For waterproofing where the annex is higher than the factory building, at least two layers of waterproofing are typically used. The first layer of waterproofing should have a 20mm-40mm groove cut into the concrete joint, and waterproof sealant applied after the finishing is inlaid. When installing the finishing at the joint between the factory building and the annex, only one end should be fixed; the other end must be free. Otherwise, thermal expansion and contraction will cause the finishing to detach and leak.  

 

5.11 Connection between brick wall and light steel roof  

 

This area is prone to leaks. Leaks at the junction of the roof panel and the cement wall are mainly caused by uneven stress, leading to cracking of the silicone sealant and the bonding surface. Solution: Prevent temperature deformation by using double-layer edge finishing; when connecting to the brick wall, the edge finishing should have a certain angle and be completely sealed; sealant should be applied before finishing.  

 

5.12 Aluminum Alloy Window Components  

 

The connection between aluminum alloy windows and corrugated steel and brick walls is a common waterproofing challenge. The main causes of leakage in this area are: gaps between the wall purlins and the aluminum alloy; inadequate sealing between the window sill and the steel structure, brick wall, and window glass and frame; large gaps between the window sill and the countertop, or backflow of water; and lack of silicone sealant during the installation of the 151 flashing trim on the window. The solutions are: ensure the flatness of the structural purlins to reduce gaps between the purlins and the aluminum alloy; completely seal all gaps at the window sill by applying silicone sealant; completely seal the gaps between the aluminum alloy and the single-groove wall, and between the single-groove wall and the glass; ensure the mortar is fully applied when tiling the countertop on the brick wall; urge the construction unit to slope the window sill before plastering to facilitate drainage; pre-apply sealant to the 151 flashing trim on the window, and avoid overlapping at the steel column location.

 

6.  Conclusion

 

Leaks in steel structure maintenance systems are not uncommon, and many factors contribute to them. To fundamentally solve the problem, careful design is crucial. A reasonable design scheme must be determined, and detailed construction of the flashing at various points-including the waterproofing layer's termination, expansion joints, drainage outlets, entrances/exits, and eaves-is essential. In terms of construction techniques, a specific waterproofing construction plan for the maintenance system needs to be developed, with coordination and cooperation among various disciplines. Only with a sound design, proper installation, reasonable construction, correct use, and follow-up service can the steel structure maintenance system be guaranteed to be completely leak-proof. In short, regardless of the installation method, as long as certain construction techniques and relevant regulations are followed, leakage problems can be reduced or avoided.