Roof edge metal can decide whether a low-slope roof holds
Wind hits roof corners and edges harder than the center. Roofing contractors should check product ratings, code rules, and warranty terms before they bid or build the perimeter.
The edge of a low-slope roof is a key defense against wind. If its metal flashing comes loose, the roof covering and insulation can follow. Water may then reach the building, according to Roofing Contractor.
The risk is not small. Roofing system failures made up about 80% of the wind loss dollars paid by commercial property insurer FM during a recent 10-year period. The annual cost was about $520 million, according to the outlet.
Wind does not press on every part of a roof in the same way. Forces can be more than 2.5 times greater at corners than in the roof’s interior. They can be more than 1.5 times greater along the perimeter.
Two standards matter
Two standards cover wind resistance around a low-slope roof perimeter. ES-1 applies to metal fascia, gravel stops, drip edges, and coping systems. GT-1 covers external gutter assemblies, including gutters, hangers, fasteners, and their connection to the building.
Gutters matter because wind can lift them. If a gutter pulls up connected edge metal, that movement can start a wider roof failure. A contractor should not treat the gutter and roof edge as separate issues during planning.
ES-1 and GT-1 are testing standards, not simple product certificates. Manufacturers send products to independent labs for testing. The right wind rating depends on the project, not just the product name.
Project details include the building’s ZIP code, height, exposure, and risk level. Exposure can change between an urban or suburban site, a site with scattered obstructions, and one near open water. Those facts can change which perimeter products meet the required wind pressure.
Both standards appear in the International Building Code. ES-1 has been part of it since 2003, while GT-1 joined in 2021. Projects must use compliant products when the governing IBC edition, or an adopted state or local code, includes those rules.
Shop-made metal can add risk
Some contractors make edge metal and gutters in their shops or at the job. The article says many do good work. Still, most contractor-made products have not gone through the independent tests required to show compliance with ES-1 or GT-1.
That gap can affect more than an inspection. Most roofing system warranties require components to come from the manufacturer or have its approval. A contractor using shop-made edge metal may lose edge-to-edge warranty coverage unless the manufacturer approves it in writing.
A materials-only warranty may not remove the contractor’s risk. If self-made metal fails and lets water into the roof, the contractor may be responsible for the damage rather than the roofing manufacturer. That makes the perimeter choice a business decision as well as an install detail.
Manufacturer-made parts can also reduce field work. They are built in a controlled setting and may include pre-punched fastener holes or snap-on fascia. Buying them can leave crew members more time for other roof work and help them move to the next job sooner.
Match the product to the building
Edge metal is not one size fits all. Different profiles fit different sites, designs, and budgets. Contractors need to match the product rating to the actual building instead of reusing the same detail on every bid.
Manufacturers may offer site visits, measurement help, calculators, estimating sheets, and install guides. Their online tools can use a ZIP code and project details to list products that meet ES-1 or GT-1 requirements. Technical staff can also answer questions before material is ordered.
This week, an owner can take four steps:
- Add the building ZIP code, height, exposure, and risk level to every low-slope roof intake form.
- Check which IBC edition and local code govern each open bid.
- Ask the roofing manufacturer to confirm compliant edge metal and gutter products in writing.
- Review warranty terms before using any shop-made edge metal, and save all approvals in the job file.