The causes and prevention measures of water leakage on the steel structure roof

1、 Steel structure roof form

As the uppermost load-bearing and outer enclosure structure of a building, the roof's enclosure function and facade modeling function are crucial to the entire building, and it is the most important part of the lightweight steel structure enclosure system that is prone to water leakage. Its main function is to resist the invasion of wind, rain, snow, and solar radiation, and to withstand the weight of the roof and the loads of wind, snow, and people on the roof.

[1] According to the materials used for light steel structure roofs, there are generally various types of color profiled steel sheets, color steel sandwich panels, color linoleum tiles, various lightweight roof panels, GRC panels, metal arched corrugated roofs, composite profiled steel sheets, and so on.

[2] Light steel structure roofing and wall materials mainly use color profiled panels or sandwich panels. The links of color profiled boards include 3600 crimped boards, concealed gusset boards for lap connections, and nailing boards. Purlins are thin-walled C-shaped or Z-shaped steel purlins with relatively light self weight, and the roof slope design is generally 1/10-1/15.

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2、 Connection of roof panel

There are two types of roof panels in steel structure system buildings: longitudinal connection and lateral connection on the roof. Long direction connection mainly refers to overlapping, that is, the uphill plate presses down the slope plate, and a special waterproof sealant and fixed special pressing strip are provided at the overlapping position. Currently, there are three main methods of lateral connection: overlapping connection, snap connection, and snap connection.

3、 Cause analysis and solution of water leakage at various parts

The main distribution of water leakage in the roof maintenance system by location is summarized as follows:

Ridge

★ Causes of water leakage: The crest at the ridge is too high, and the ridge cover cannot ensure waterproofing; No glue or silica gel shall be placed in the longitudinal overlap to form gaps and cause water leakage; The longitudinal overlap of the roof ridge cover plate is connected with rivets, and the rivets are pulled apart due to insufficient heat expansion and cold shrinkage strength, resulting in water leakage; No plug is laid between the ridge cover plate and the roof panel, or the plug is placed improperly and falls off to form water leakage.

★ Solution: Make the ridge cover wider, and make the slope larger; Laying glue or silica gel at the overlap; Replace the suture nail; The plug should match the plate type plate, and the plug should be laid with cement paste or silicone.

Roof gas tower part

★ Cause of water leakage: no foam plug is placed under the closing edge at the junction between the gas tower and the roof, and no mastic or silica gel is laid for the longitudinal lapping of the closing edge; The roof outer plate is not boarded at the junction of the gas tower; The opening part of the pillar of the gas tower structure has not undergone waterproof treatment; There are potential water leakage hazards in the fabrication and installation of the gas tower itself.

★ Solution: foam plugs shall be laid before edge closing installation, and mortar or plugs shall be set for longitudinal overlap and fixed with suture nails; Before installing the gas tower, the roof panel must be pulled up; The construction party of the gas tower is required to carry out waterproof treatment on the opening parts after the completion of the gas tower structure; Inspect the installation quality and waterproofing of the gas tower.

Daylighting panel position

★ Causes of water leakage: The type of the daylighting board does not match the type of the roof panel, and the wave peaks on both sides of the daylighting board are higher than the roof panel. After installation, the sealing is too tight to form a pressure difference between the inside and outside of the daylighting board, and capillary water leaks from the gaps on both sides of the daylighting board into the interior of the roof; The longitudinal overlapping length of the daylighting board is not enough, and the adhesive loses its viscosity due to aging; The longitudinal glue falls off; The lighting plate and color steel plate are rigidly overlapped, and the gap between them is not sealed.

★ Solution: Apply waterproof screws to the upper part of the wave crest; The edge closing plate at the daylighting board should be tightly sealed with the daylighting board, the mastic on both longitudinal sides should be widened, and the upper part of the wave crest should be paved to prevent capillary water from infiltrating.

Roof opening position

★ Causes of water leakage: The opening was not subject to waterproof treatment according to the design node, and the steel plug was not laid with waterproof glue and silicone; The reserved area around the opening is small, and the rainwater flow is not smooth, which is easy to accumulate water; No waterproof treatment was carried out for the edge bonding around the opening; There are no structural members added around the inside of the opening, forming low concave water accumulation; There is a water blocking phenomenon in the waterproof construction, resulting in ponding.

★ Solution: Construct according to the design drawings and strictly follow the construction process, laying mortar and silica gel; The reserved range around the opening must meet the drainage requirements; After opening holes in the wall and roof, waterproofing treatment must be carried out subsequently; Purlins or angle steel structures should be added as much as possible to reduce the deformation of the enclosure during the opening of the rear added enclosure; Waterproof construction and installation must be tight and smooth to ensure smooth water flow.

Cornice part

★ Cause of water leakage: cornice is the main source of the water leakage problem. foam plug is not added to the installation of roof outer plate, and the roof outer plate is not pulled down; The length of the outer wall panel is insufficient, and the cornice part is not provided with waterproof edge trimming.

★ Solution: foam plugs shall be placed at the same time when installing the roof outer plate, and the roof outer plate shall be pulled down 30 degrees; Edges shall be added at the cornice according to the design requirements.

Gutter part

★ Causes of water leakage: There are gaps in the welded joints of the inner gutter, forming water seepage; The diameter design of the gutter and rainwater pipe is too small, which does not match the slope length of the plant; The end of the gutter is not provided with a closure plate; The length of the roof outer plate extending into the gutter is insufficient, and water will pour into the interior of the plant.

★ Solution: Increase the depth of the gutter appropriately to ensure that the rainwater in the gutter does not exceed the overlap joint.

Connection between brick wall and light steel roof

★ Causes of water leakage: This part is prone to potential water leakage, and the joint between the roof panel and the cement wall leaks. The main reason is that the stress is not synchronized, resulting in cracking of the silicone adhesive and the bonding surface, leading to water leakage.

★ Solution: To prevent temperature deformation, use twice edge closing and connection processing; When connecting to brick walls, the edges should be at a certain angle and completely sealed; Sealant shall be applied in advance between the edges.

4、 Analysis of other causes of water leakage in the maintenance system

Design reasons

① The roof rainwater system is not provided with overflow measures according to the specifications. When the rainstorm intensity exceeds the drainage capacity of the rainwater system, it will exceed the lap joint, or even overflow the roof, causing accidents;

② The number of downspouts is insufficient, and rainwater flows far away along the gutter for a long time, resulting in backwater; The upper part of the wall outer plate is not provided with an L-shaped edge trimming piece, causing a potential water leakage hazard inside the gutter;

③ The design of color steel flashing fittings is unreasonable and cannot achieve waterproof effect.

④ The specification specifies the component deformation control values, including the deflection of purlins L/180, and the deflection of roof beams L/180 (where L is the span of the flexural member). If the cross section design of roof purlins is too small and the spacing is too large, the deformation of purlins and profiled plates will be too large under wind load;

⑤ The effects of structural deformation, temperature difference deformation, drying shrinkage deformation, vibration, etc., were not fully considered, and the fortification did not meet the needs of deformation of the base layer.

⑥ The roof slope of portal frame light houses should be taken as 1/8-1/20, and the larger value should be taken in areas with high rainfall. The roof slope in southern areas should not be less than 5%. In practical design projects, the roof slope of many projects is too small, and roof rainwater cannot be timely discharged to the gutter.

Improper material selection

① Rainwater pipes are made of plastic pipes with poor strength, and steel structure plants are prone to damage from installation to production and operation.

② The steel plate used for the gutter is relatively thin, and the welds are prone to problems.

③ Failure to select the appropriate type of lighting board and roof color board based on the slope of the roof results in small wave peaks and too few lateral laps, which is not conducive to drainage.

④ The color plate of the enclosure is too thin. After a period of use, the outer plate is corroded or deformed due to temperature, and the gap between the plates increases.

⑤ The quality of the galvanized layer on the base plate of the profiled plate is poor, and the coating is too thin, resulting in a short service life of the profiled plate and easy to rust and damage;

⑥ The poor quality of the self tapping screw gasket is prone to cracking, and the glass sealant is prone to aging.

⑦ The gusset plate is significantly deformed, and the height and spacing of the adjacent two plates are different; The gusset plate pull nails shall be waterproof.

Structural measures

① The plug has an effect on water leakage caused by joints and should not be ignored. For example, ensure that the plug between the color steel plate and the ridge cover plate is installed in place, apply silicone sealant to the lower part of the plug between the daylighting plate and the ridge cover plate, and set a steel plug at the crest end of the color steel plate at the roof opening;

② When overlapping, the gap is easily affected by temperature and becomes larger, and sufficient overlapping length should be reserved;

③ Water should be drained rather than blocked. Generally, during installation, sealant should be applied to the inside of the steel plate, as more is beneficial;

④ Sufficient attention must be paid to the adverse effects of thermal expansion and contraction of the steel structure roof enclosure system, and reasonable structural measures must be taken.

During use

① Arbitrarily increasing loads on roof purlins leads to deformation of the roof panel.

② The rainwater has a lot of dirt accumulation and water blocking.

③ The waterproof adhesive and sealant are aging and lack of necessary maintenance during use.

Conclusion

There are many factors that cause water leakage in the steel structure maintenance system. To fundamentally solve the problem, it is necessary to take the design seriously, determine a reasonable design scheme, and properly handle the detailed structure of the flashing parts such as one end (end of the waterproof layer), two joints (deformation joints, dividing joints), three openings (water outlet, entrance, cornice), and four (parapet wall root, equipment root, pipe root, chimney root); From the construction perspective, formulate a special waterproof construction plan for the maintenance system, and coordinate and cooperate with each other in various disciplines. Perfect design, installation in place, reasonable construction, proper use, and follow-up service can ensure that the steel structure maintenance system is watertight. In short, no matter what form of installation is used, as long as certain construction processes and relevant regulations are followed, the occurrence of water leakage can be reduced or avoided.

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