How to Install RoofingFoil™ with Spray Foam Insulation in New Construction

New Construction Installation Guide

Create a reflective air gap beneath new roof decking while preparing the attic for a sealed, spray-foamed roofline.

This method installs RoofingFoil™ + Underlayment across exposed rafters, with foam spacer strips above it to separate the foil from the roof deck. The attic-side surface can then be incorporated into a professionally designed spray foam insulation assembly.

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What RoofingFoil Does

The aluminum foil surface reflects up to 97% of radiant heat incident on it. The reflective face needs an adjacent air gap to reduce radiant heat transfer.

What Spray Foam Does

A properly designed spray foam system provides thermal resistance and helps establish a continuous air barrier at the roofline. The two products address different heat-transfer mechanisms.

What You'll Need

RoofingFoil™ + Underlayment All-in-One
Rigid foam board cut into approximately 2-inch-wide by ½-inch-thick strips
Plastic cap roofing nails or other suitable temporary fasteners
Optional spray adhesive for temporarily positioning spacer strips
Measuring tape and utility knife
Roof decking and engineered fastening materials

Air Gap: Plan for a minimum ½-inch separation between the reflective foil surface and the underside of the roof decking. The cavity can be designed as vented or unvented; the attic below remains sealed.

Step-by-Step Installation

Prepare the Exposed Roof Rafters

Begin before roof decking is installed. For a vented cavity, plan an inlet near the eaves and a corresponding outlet at the ridge.

Start the RoofingFoil a few inches back from the drip-edge area only where the roof design provides a protected, continuous inlet path.

Detail the inlet to resist rain, pests, and debris. If the cavity is unvented, do not leave unintended exterior openings.

Roll RoofingFoil Across the Rafters

Pull RoofingFoil™ + Underlayment across the tops of the rafters, with the reflective aluminum side facing upward toward the future airspace.

Keep it reasonably taut and secure temporarily with a few plastic cap nails. Overlap adjacent runs approximately 4–6 inches, following applicable product instructions for seams.

Install the Foam Spacer Strips

Cut rigid foam board into strips approximately 2 inches wide and at least ½ inch thick.

Position the strips over the rafters on top of RoofingFoil. A small amount of spray adhesive or temporary cap nails can hold them until the roof deck is installed.

The strips maintain the air gap between the foil and the underside of the roof deck. A larger separation may be used when accounted for in the roof design.

Structural Note: Foam spacer strips are not structural battens. A qualified designer should confirm sheathing support, fastener length, uplift resistance, and local code compliance before construction. The approved fastening design must account for the spacer thickness and provide proper attachment to structural framing.

Install the Roof Decking

Install the decking above the foam spacers using the approved structural fastening plan.

Maintain the designed cavity without crushing or blocking the air gap.

If the roof is designed for soffit-to-ridge airflow, preserve a continuous channel and leave the required ridge opening for the specified ventilation system.

Complete the Roofing System

Finish the roof with the specified roof-covering underlayment, flashing, vents, and roofing material.

In this assembly, RoofingFoil is located below the structural decking. It does not replace any water-shedding underlayment required above the decking.

Prepare the Attic Side for Spray Foam

After the roof is completed, the insulation contractor can evaluate the attic-side RoofingFoil surface for application of the specified spray foam system.

The finished insulation and air-barrier assembly should connect to the adjoining walls to create a sealed attic enclosure.

Confirm product compatibility and the approved assembly with the insulation contractor before application.

Roof Assembly: Top to Bottom

Roof Covering + Required Underlayment
Structural Roof Decking
½-Inch Minimum Air Gap (Optionally Vented)
RoofingFoil™ + Underlayment, Reflective Side Up
Roof Rafters + Specified Spray Foam Assembly
Sealed Attic / Interior

Spacer strips sit over the rafters between RoofingFoil and the decking. This is a conceptual layer order, not a structural or code-approved construction detail.

Vented Air Gap

Outside air can enter at a properly protected eave inlet, pass above RoofingFoil, and exit near the ridge.

This may help remove heat from beneath the roof deck. The channel must remain separate from the sealed attic.

Unvented Air Gap

RoofingFoil still works as a radiant barrier when an air gap is maintained without airflow.

The roof assembly must be designed for its intended unvented configuration.

How Does This Compare with a Double-Deck Roof?

A double-deck system uses an additional layer of structural sheathing separated by framing or furring to create a cavity.

It can accommodate radiant barrier materials and a spray-foamed roofline, but requires additional decking, materials, and labor, and adds roof weight.

The RoofingFoil + spacer approach described here creates the reflective airspace without a second complete layer of roof decking. Its structural details still need project-specific approval.

Before You Begin: Coordinate this roof assembly with your builder, roofing contractor, structural designer, and spray foam installer. A qualified designer should confirm sheathing support, fastener length, uplift resistance, and local code compliance. Verify material compatibility, fire-safety requirements, and the complete roof assembly before installation.

Build Radiant Heat Control Into Your New Roof

Installing RoofingFoil during framing lets you create a reflective air gap before decking goes on, while preparing for a sealed, spray-foamed attic below.

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Questions about your project? Call 1-800-595-8772.