Overview

Fanfold insulation — typically 0.5-inch polyisocyanurate or expanded polystyrene panels — is used as a base layer beneath TPO membrane on mechanically fastened flat roofing systems. It provides a smooth, uniform substrate for the membrane and a thermal improvement over bare decking. At Trust Roofing, fanfold installation follows a specific process to ensure the panels are laid flat, tight, and properly staggered before membrane installation begins.

Our Field Standards

Fanfold insulation installation follows Trust Roofing field standards.

Field standards include:
* The existing deck surface is inspected and confirmed clean, dry, and structurally sound before fanfold is installed
* Panels are installed perpendicular to the direction of the TPO rolls above
* Joints between panels are staggered — no continuous seam across the full deck width
* Panels are fastened or adhered per the project specification — confirm with the project manager
* No gaps larger than 0.25 inches between panels are allowed
* Completed fanfold installation is confirmed flat before TPO installation begins

Our Process

Preparing the Deck

* Walk the entire deck and confirm it is clean, dry, and free of sharp protrusions
* Remove any debris, nails, or material that would create a high point under the fanfold
* Confirm there is no standing water or moisture on the deck surface

Installing Fanfold Panels

1. Begin at one edge of the deck and work toward the opposite side
2. Orient panels perpendicular to the planned TPO roll direction
3. Stagger panel joints — offset adjacent rows by at least 12 inches
4. Press each panel flat against the deck surface — no bowing or gaps at edges
5. Fasten or adhere per the project specification

Managing Penetrations

* Cut panels to fit tightly around all penetrations — pipes, vents, curbs
* No more than 0.25 inches of gap around any penetration
* Fill gaps at penetrations with compatible insulation material

Final Inspection

* Walk the full deck — confirm no panels are rocking, bowing, or poorly aligned
* Check all edges and perimeter areas — panels must be tight to the deck edge
* Photograph the completed fanfold installation before membrane is rolled out

Roofing Terms

Fanfold Insulation

Thin rigid insulation panels, typically 0.5-inch polyisocyanurate or expanded polystyrene, used as a base layer beneath TPO membrane on mechanically fastened flat roofing systems to provide a smooth, uniform substrate.

TPO (Thermoplastic Polyolefin)

A single-ply roofing membrane used on flat and low-slope roofs, welded at seams with hot air to create a continuous, watertight surface. The most widely installed flat roofing membrane system on commercial and residential flat roofs in Florida.

Mechanically Fastened System

A TPO installation method where the membrane is attached to the roof deck using metal fastener plates driven through the membrane edge, as opposed to fully adhered or ballasted systems.

Substrate

The surface over which roofing materials are installed, in a mechanically fastened TPO system, the fanfold insulation layer serves as the substrate for the membrane and must be flat and continuous.

Florida Building Code Flat Roof Requirements

FBC requires flat roofing systems to achieve a minimum drainage slope and meet specific membrane attachment standards, including fastener density requirements that increase at perimeter and corner zones due to higher wind uplift loads.

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