Mechanically attached

Plain-English definition

A membrane attachment method using rows of screws and plates driven through the membrane edge into the roof deck. The next sheet overlaps and is sealed over the fastener row, so the finished roof shows no exposed fasteners — they are hidden inside the seams.

Why it matters to you

Verified: Mechanical attachment is generally the fastest and most economical way to secure a single-ply membrane, which is why it is so common on large roofs (GAF — single-ply attachment methods). The trade-off is that the membrane is only held at the fastener rows, so wind can pull air into the assembly and make the sheet billow and flutter between rows — behavior that fully adhered and induction-welded systems reduce or eliminate. For owners, the practical questions are whether the proposed fastener pattern matches the calculated wind uplift pressures for your building’s zones, and whether the fasteners are compatible with your deck type — a bid that is cheaper because it thins out the fastening is not a bargain (see adhered vs. mechanically attached).

Technical detail

Fastener row spacing and in-row spacing are engineering outputs, not installer preference: manufacturer requirements and building codes set the pattern, and under ANSI/SPRI WD-1 (2025) the tested uplift capacity of the assembly is compared against the design load for each roof zone. Because design pressures rise from the field to the perimeter and corners, fastening density typically tightens toward roof edges. Fastener pullout resistance depends on the deck (steel, wood, concrete), which is why deck condition and type are verified before this method is specified.