GreenGuard XP38 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.

How can I use foam sheathing in place of wood sheathing and maintain structural stability?

XPS foam sheathing not only offers better insulation than wood sheathing, but it also provides water resistance. You can use GreenGuard XPS foam sheathing in place of wood sheathing by employing alternate bracing methods such as “let-in bracing” or steel strapping to achieve structural properties. Another alternative is to use wood sheathing in the corners to achieve structural properties and foam sheathing in the non-structural portions of the wall. This approach is done following the “prescriptive method” outlined in the codes. Another simple option is to sheath the house completely in wood and install a layer of XPS insulation on the exterior as added insulation. Please reference our Technical Evaluation Report - TER 1410-09 / Attachment of Exterior Wall Coverings through Kingspan GreenGuard XPS Sheathing to Wood or Steel Wall Framing.

Some GreenGuard siding underlayments have a relfective 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.

Documents

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

Technical Info

• GreenGuard XP38 Fanfold can be used in the residential, commercial, etc. applications.
• GreenGuard is Extruded Polystyrene (XPS)
• GreenGuard XP38 is 4' wide and 50' long

Code Compliance

• Code Compliance Research Reports: CCRR-1022