GreenGuard Q250 Fanfold Underlayment

Does fanfold provide good insulation value?

The primary purpose of fanfold is to level out the walls, so the new siding goes on straight. Fanfold does provide some additional R-Value to the wall depending on the thickness. 

Should the reflective surface be placed to the outside or the inside?

Since reflective surfaces are designed to reflect radiant heat, it is common practice to install the radiant surface to the predominantly warm side of the wall. In an extremely cold climate, that would mean installing with the reflective surface inward. In a hot climate, it would be installed with the radiant surface outward. In climates that are more balanced, it may be installed either way, depending on whether the objective is to reduce heat loss in winter or reduce heat gain in summer.

Some GreenGuard siding underlayments have a reflective surface and claim a higher R-Value. How does this work?

Reflective surfaces reflect (do not emit) radiant heat. For example, our 3/8” thick siding underlayment has an R-Value of 1.5. With a reflective surface, the effective R-Value of that product can be as high as 3.5, when installed using a ½” uniform, parallel dead air space on the reflective side. This follows the “ASHRAE Handbook of Fundamentals” basic principles of reflective insulation properties. With the air space partially achieved, the effective R-Value is something between the 1.5 of the foam and the maximum 3.5. Be aware that some manufacturers may make misleading claims of very high R-Values achieved with reflective surfaces. 

Should I install the fanfold or building wrap first?

Depends. If you are doing a full siding tear off and replacing the whole window units it is recommended to install the fanfold first and then the building wrap on top. You will then install the windows on top of these layers and flash accordingly. If you are keeping the existing windows, it is often easier to install the building wrap first to flash it to the existing window and then install the layer of fanfold on top.

Can fanfold siding underlayment be used in place of building wrap?

GreenGuard siding underlayments are in compliance with the ICC-ES “Acceptance Criteria for Foam Plastic Sheathing Panels Used as Weather–resistive Barriers” (AC71). This means that GreenGuard fanfold siding underlayments may be used in either new or retrofit construction applications without an additional water-resistive barrier (felt building paper or building wrap), when they are installed in strict accordance with the installation instructions.

Documents

1. Insulation Board Line Sheets
2. Product Data Sheet
3. Safety Data Sheet (SDS)
4. Installation Guides

Technical Info

• GreenGuard Q250 Fanfold can be used in the residential, commercial, etc. applications.
• GreenGuard is Extruded Polystyrene (XPS)
• GreenGuard Q250 is 4' and 48' long

Code Compliance

• Code Compliance Research Reports: CCRR-1022