Mechanically Fastened Systems
Mechanically attached EPDM installation including fastener and plate types, in-seam attachment methods, FM Global wind uplift zones, and fastener density calculations.
- Describe in-seam plate attachment and how it secures the EPDM membrane
- Calculate fastener spacing for FM 1-60, 1-90, and 1-120 wind uplift ratings
- Identify wind uplift zones (field, perimeter, corner) and explain why fastener density increases at edges
- Select correct fastener types and lengths for steel deck, wood deck, and concrete substrates
Lesson 1
How Mechanically Fastened EPDM Works
The Concept of In-Seam Attachment
In a mechanically fastened EPDM system, the membrane is not glued to the substrate. Instead, it is held in place by rows of fasteners and plates located at each seam overlap. The fastener penetrates the bottom EPDM sheet and anchors into the deck below, while the top sheet overlaps and is spliced over the fastener plates, concealing and waterproofing the attachment point.
This is called in-seam attachment because every fastener is hidden within a membrane seam. No fasteners penetrate the exposed top surface of the membrane.
The attachment plate (also called a barbed seam plate or membrane plate) is a round or rectangular metal disc, typically 2-3 inches in diameter, made from galvanized steel or stainless steel. Barbed plates have small teeth on the upper surface that grip the underside of the top membrane sheet, helping prevent wind-induced membrane flutter.
Advantages and Limitations
Mechanically fastened EPDM is the fastest attachment method, making it popular for large, open-field roof areas. It does not require adhesive (except at seams), so it can be installed in a wider range of weather conditions and temperatures. It also works with 45-mil membrane, reducing material costs.
However, mechanically fastened systems are more susceptible to membrane flutter (billowing) in high winds between the fastener rows. The membrane can fatigue over time at the fastener plate edges if wind uplift loads are underestimated. For this reason, fastener spacing must be calculated based on tested wind uplift ratings, not guesswork.
Membrane Sheet Width and Row Spacing
Standard EPDM membrane rolls come in widths of 10 feet, with available widths ranging from 5 to 50 feet. In a mechanically fastened system with 10-foot-wide sheets, the fastener rows are approximately 10 feet apart (one row per seam). Wider sheets mean fewer seam rows and fewer fasteners, but wider unsupported spans can increase flutter.
Mechanically fastened EPDM uses in-seam plates hidden beneath overlapping membrane sheets. Every fastener is concealed within a seam - no fasteners penetrate the exposed membrane surface.