Through-Fastened Panel Systems
Screw patterns and spacing for through-fastened metal panels, washer types and neoprene seal requirements, pre-drill procedures, and purlin spacing for corrugated and ribbed profiles.
- Lay out correct screw patterns for through-fastened panels on purlins at 24-inch and 60-inch spacing
- Select the correct washer type (neoprene bonded, EPDM) for panel gauge and application
- Determine when pre-drilling is required versus self-drilling screws
- Calculate purlin spacing based on panel profile, gauge, and design load
Lección 1
Screw Patterns and Fastener Placement
How Through-Fastened Panels Work
Through-fastened panels are secured by driving screws through the panel face directly into the supporting purlins or solid deck below. Each screw penetration creates a potential leak point sealed by a washer, making fastener selection and driving technique critical to the system's waterproofing integrity.
Screw Placement - Crown or Valley
The two options for screw placement on corrugated or ribbed panels are:
Crown fastening (into the rib): The screw is driven through the top of the raised rib (crown) of the panel. This keeps the fastener head above the water line, reducing leak risk. However, crown fastening requires longer screws (to span from the rib top down to the purlin), and the washer must seal against a curved surface. Crown fastening is common in residential and light commercial applications.
Valley fastening (into the flat): The screw is driven through the flat (valley) between ribs, where the panel sits directly on the purlin. This provides better pullout resistance because the screw is shorter and the panel is clamped tightly against the purlin. Valley fastening is the dominant method for commercial and industrial applications and is recommended by most panel manufacturers.
Crown Fastening (Into Rib)
Screw location: Through top of raised rib
Leak risk: Lower - above water line
Pullout: Lower - longer screw, curved surface
Common use: Residential, light commercial
Valley Fastening (Into Flat)
Screw location: Through flat between ribs
Leak risk: Higher - in water channel
Pullout: Higher - tight clamp to purlin
Common use: Commercial, industrial (manufacturer recommended)
Standard Screw Patterns
The screw pattern depends on the panel profile and the location on the roof:
Field of roof: One screw per rib at each purlin crossing. For a panel with ribs at 9-inch spacing crossing purlins at 5-foot spacing, you would have one screw every 9 inches at each purlin line.
Eave and ridge: Two screws per rib at the eave and ridge purlin lines. The doubled pattern resists the higher wind uplift at these locations.
Sidelaps: Where two panels overlap at the side, screws are placed through both panels at the overlap rib. Sidelap screws are typically stitch screws (short screws connecting panel to panel, not reaching the purlin) placed at 12-24 inches on center between purlins.
Valley fastening (into the flat) is the manufacturer-recommended method for commercial through-fastened panels because it provides superior pullout resistance. Double the screw count at eave and ridge purlin lines to resist higher wind uplift loads.