fly-in

A fly-in is a method of installing roll materials, typically roofing membranes or underlayment, where the dry sheet is positioned and pressed directly into wet bitumen, adhesive, or mastic that has already been applied to the substrate. The installer unrolls the material from above and lowers it into place, allowing gravity and hand pressure to seat it into the adhesive bed. This contrasts with pre-glued membranes where adhesive is built into the back of the roll itself.

The technique is most common with asphalt-saturated felt, fiberglass reinforced membranes, and synthetic polymers used in low-slope roof systems. The adhesive is typically hot-applied bitumen, cold-process bitumastic, or water-based acrylics, depending on the material specification and climate. A single installer can manage the fly-in process by unrolling the dry sheet while a second worker applies adhesive to the deck in advance, creating an overlapping installation sequence that moves across the roof surface.

Adhesion and Failure Modes

Success in fly-in installation depends on achieving consistent contact between the dry material and the adhesive layer before the adhesive begins to set or skin over. If adhesive dries too quickly in warm conditions, the sheet will not embed fully and will develop wrinkles, voids, and weak spots prone to peeling. Conversely, excessive adhesive can telegraph through the membrane or cause material to slip during installation. The installer must judge timing carefully and apply adequate pressure, typically with a hand roller, to ensure full wetting of the entire sheet width.

Fly-in installation is faster than some alternatives and requires less specialized equipment than fully mechanized systems, making it economical for small to medium roof areas. However, it demands skilled labor and favorable weather. Wind can disturb the dry sheet before adhesion occurs, rain can contaminate the adhesive, and temperature extremes alter both the viscosity of the bitumen and the handling properties of the membrane. The method also generates more waste than pre-glued systems because trimming and overlaps must be handled on site.

The name reflects the literal action: the dry roll is "flown in" or suspended briefly above the adhesive before being laid down and bonded. This distinguishes the approach from "peel-and-stick" self-adhesive membranes and fully adhered systems where material and adhesive are unified before installation.