1.What are the core principles?
The "top over bottom" principle: When overlapping horizontally or vertically, the upper or outer panel must overlap the lower or inner panel to prevent rainwater from seeping in due to gravity or capillary action.
Proper sealing: Use specialized sealing materials at necessary joints to eliminate any path for water penetration.
Prevention of electrochemical corrosion: Although both galvanized layers and color-coated steel sheets are corrosion-resistant, electrochemical corrosion can still occur under certain conditions if the two metals are exposed to an electrolyte (such as rainwater) for an extended period. Therefore, physical isolation and sealing are crucial.
2.What are the methods and steps for horizontal overlapping of roof sections?
Procedure: Place the upper panel down on top of the lower panel. The overlap length depends on the roof slope and local wind load, typically no less than 150mm-250mm. The gentler the slope, the longer the overlap.
Key Steps:
Clean the contact surface: Thoroughly remove dust, oil, and moisture from the crest of the lower panel in the overlap area.
Apply sealant: Apply a continuous strip of neutral silicone weather-resistant sealant to the overlap area of the lower panel. The sealant strip should be approximately 8-10mm in diameter.
Immediately secure the overlap: Press down the upper panel and align it. Secure both panels to the purlin together at the crest using self-tapping screws. The screws should be driven into the top of the crest, not the edge of the overlap.
Extrusion molding: The extruded sealant will form a uniform, waterproof sealant line, perfectly filling the gap.
3.What are the methods and steps for longitudinal overlapping?
Method: This is a high-end system of concealed fasteners. The sides of the panels are pre-rolled into special male and female ribs.
Key Steps:
Positioning: The male rib of one panel is embedded into the female rib of the adjacent panel.
Interlocking: Using a specialized seam-locking machine, the male and female ribs are tightly interlocked along the joint, forming a vertical joint up to 25-40mm high.
Advantages:
No Through-Screws: Screws are hidden beneath the panels and fixed to the purlins, eliminating holes in the roof surface and fundamentally preventing leaks.
Thermal Expansion and Contraction: The vertical joint system allows the panels to slide due to temperature changes, avoiding stress.
High Wind Resistance: The locked vertical joint has extremely high wind uplift resistance.
Applicability: This method requires specialized equipment and pre-formed vertical joint panels, and is typically used for the roofs of large public buildings and industrial plants.
4.What are the methods and procedures for handling the jointing of simple or temporary buildings?
Method: Overlapping + Specialized Accessories
Instructions: Simply overlap one board onto another, creating a trough or crest.
Key Steps:
Use a waterproof cap: Above the overlap, use a color-coated steel waterproof cap and secure it on both sides with screws.
Apply sealant: Apply sealant to the area below the contact point between the cap and the board to enhance waterproofing.
Advantages: Simple construction, low cost.
Disadvantages: Less aesthetically pleasing, less durable than vertical joint systems.
5.What are the key considerations and material selection guidelines?
Sealant Selection:
A neutral, weather-resistant silicone sealant must be used. Avoid using acidic silicone sealant, as it will corrode the galvanized layer and color coating.
The sealant color should ideally match the panel color for aesthetic purposes.
Fastener Selection:
Self-drilling screws with EPDM waterproof washers must be used.
The screw length must be sufficient to penetrate all panels and embed at least 25mm into the underlying structure (such as purlins).
Screws should be driven in vertically and tightened until the washer is slightly deformed and flush against the panel surface. Overtightening should be avoided to prevent washer breakage or panel dent.
Overlap Direction:
On roofs, transverse overlaps must be with the water flow, i.e., the upper panel overlaps the lower panel. Overlaps against the water flow are strictly prohibited.
Cleaning and Protection:
Ensure all overlapping surfaces are clean, dry, and free of oil before application.
Clean up any excess sealant promptly after application.