Which Side of Metal Roofing Panels Overlap

Metal roofing installation requires attention to how panels overlap to keep water out, resist wind, and ensure long-lasting performance. This article explains the key principles for deciding which side of metal roofing overlaps, practical installation tips, and manufacturer considerations for corrugated, exposed-fastener, and standing-seam systems.

Panel Type	Typical Overlap Direction	Key Consideration
Corrugated/Trapezoidal	Higher Rib Over Valley	Sealant at Valleys and Side Laps
Exposed-Fastener Sheets	Side Lap Overlapping Sheet Toward Downwind	Butyl Tape/Sealant & Correct Fastener Location
Standing Seam	Seams Interlock Vertically; Side Lap Not Typical	Crimp/Seam Direction Per Manufacturer

Basic Principles Of Metal Roofing Overlaps

Overlaps exist to channel water away from joints and to create wind resistance. The fundamental rule is that the overlapping panel must cover the joint in the direction water and wind will try to enter. This principle applies to side laps, end laps, and vertical seams across all metal roofing types.

Which Side Of Metal Roofing Overlaps: The Direct Answer

For most metal roof panels, the higher profile or male rib overlaps the adjacent lower valley or female side. This means the exposed edge of the panel that sits above the valley typically goes over the lower side so water sheds off the top of the overlap instead of collecting inside the seam.

Corrugated And Trapezoidal Panels

Corrugated panels have alternating ribs and valleys. Installers typically position panels so the overlap places a rib over the valley of the adjoining sheet. This reduces capillary action and keeps fasteners and sealant from direct water exposure, improving weather tightness.

Side laps on corrugated panels usually require 1–2 ribs of overlap and continuous or spot sealant in the valley. End laps should be staggered and include a backing strip and sealant to prevent leaks at the butt joints.

Exposed-Fastener Single-Skin Sheets

For exposed-fastener systems, the exposed edge of the first sheet is placed under the overlapping edge of the next sheet so the overlap covers the fasteners of the underlapped sheet. Fasteners should be located on the upper side of the valley or per manufacturer guidance to prevent direct water entry.

Butyl tape, foam closures, or lap sealant are commonly used at the side lap to create a secondary water barrier. Proper fastener spacing and placement are essential to avoid distortion and leaks.

Standing Seam Roof Panels

Standing seam systems differ: panels have raised seams that interlock or are mechanically seamed. There is not a traditional side lap like single-skin sheets; instead, panels interlock vertically and are seamed to form a continuous weather-tight joint. Seam orientation and roll-form direction must follow manufacturer instructions to ensure proper overlapping engagement.

How Wind Direction Affects Overlap Orientation

Wind-driven rain can force water under improperly oriented laps. Installers should orient side laps so the overlapping panel faces the prevailing wind or so that laps are stepped away from the wind direction. If prevailing winds come from the west, panels are often installed left-to-right so the left panel laps over the right to minimize wind-driven water entry.

End Laps And Roof Slope Considerations

End laps should always be oriented so the top sheet overlaps the lower sheet, allowing water to flow over the lap. On low-slope roofs, longer end lap overlaps, additional sealants, and sometimes plywood underlayment or a waterproof membrane are necessary. Low slopes increase leak risk, so manufacturer minimum slope requirements must be followed.

Fastening And Sealant Best Practices

Fastening patterns affect overlap performance. For exposed-fastener panels, fasteners placed in the flat area next to the rib reduce water intrusion. For hidden-fastener or standing seam systems, fasteners are often clipped under the seam. Always use neoprene-washer screws, correct length, and corrosion-resistant materials per manufacturer specs.

Sealants—compatible with the panel coating—should be applied at side laps and end laps where recommended. Overuse of sealant can impede drainage; underuse allows leaks. Proper bead size and placement are critical.

Common Installation Mistakes To Avoid

• Reversing Overlap Direction: Installing panels so the underlapped sheet covers the windward side increases leak risk.
• Insufficient Overlap: Failing to overlap by the required ribs or inches leads to water and wind intrusion.
• Incorrect Fastener Location: Driving screws through the valley or exposed to direct runoff accelerates leaks and corrosion.
• Ignoring Manufacturer Instructions: Each panel profile and coating has specific requirements; deviation voids warranties.

Manufacturer Guidance And Warranty Considerations

Different manufacturers and panel profiles specify exact overlap amounts, fastener patterns, and seam orientation. Following manufacturer installation instructions is essential both for performance and to preserve warranty coverage. Installation guides often include diagrams showing which side overlaps and how many ribs to overlap.

Practical Step-By-Step For Determining Overlap On A Job

1. Review manufacturer documentation for panel profile and overlap requirements.
2. Assess prevailing wind direction and orient panels to place overlaps away from wind-driven rain.
3. Start at the eave and work toward the ridge; ensure end laps are stepped and sealed correctly.
4. Overlap ribs or valleys per profile—typically the male rib over the female valley.
5. Install fasteners in specified locations and apply sealant/closures where recommended.

Inspection And Maintenance For Longevity

Periodic inspection of overlaps, sealant integrity, and fastener tightness helps maintain roof performance. Look specifically at side laps, end laps, and flashing interfaces, especially after storms. Replace degraded sealant and tighten or replace loose fasteners with appropriate washers.

When To Consult A Professional

Complex roof geometry, low slopes, coastal or high-wind zones, and attachment to existing roofing systems can complicate overlap decisions. Professional roofers or structural engineers can interpret manufacturer specs and local building codes to ensure the correct overlap orientation and secure installation.

Summary Table: Quick Overlap Rules By Panel Type

Panel Type	Side Overlap Rule	Sealant/Fastener Note
Corrugated	Higher Rib Over Lower Valley	1–2 Ribs Overlap; Seal Valleys
Exposed-Fastener	Overlapping Edge Covers Fasteners Of Underlap	Butyl Tape; Fasteners On Flats
Standing Seam	Panels Interlock Vertically; Follow Seam Direction	Mechanical Seaming; Clips Under Seam

Keywords And SEO Notes

This article targets the search phrase “Which Side Of Metal Roofing Overlaps” and related queries such as “metal roofing overlap direction,” “corrugated panel overlap,” and “standing seam overlap.” Clear answers and action steps improve search relevance for homeowners and installers seeking guidance on overlap orientation.

For best results on a particular project, cross-reference this guidance with the metal roofing manufacturer’s installation manual and applicable local building codes.