House Wrap vs Fanfold vs Foam Board | EPHI

What House Wrap Does

House wrap acts as a water-resistive layer behind the siding when it is properly installed and flashed. It helps manage incidental moisture while allowing the wall system to dry in the way the product is designed to perform.

What Fanfold Does

Fanfold is a thin insulation or underlayment layer often used to create a smoother surface behind vinyl siding. It can help reduce small wall irregularities, but it is not a substitute for proper water management or damaged-wall repairs.

What Foam Board Does

Foam board can add continuous insulation and help improve the wall surface when selected for the right application. The product thickness, seams, flashing, and siding attachment details all need to be planned correctly.

Compare the Full Scope

A siding estimate should explain what will happen behind the old siding, not only what the new panels will look like. Compare house wrap vs fanfold vs foam board wall repair, flashing, moisture protection, insulation layers, and trim details before choosing an option.

House Wrap vs Fanfold vs Foam Board

• House Wrap Prioritizes Superior Moisture Management: House wrap acts as a breathable barrier designed specifically to keep liquid water out while letting interior water vapor escape. It does not provide any structural insulation value or stop thermal bridging through your exterior wall studs. You must install it directly over the wood sheathing to protect the home framework from rot.
• Fanfold Board Smooths Walls For Siding Updates: Fanfold insulation consists of thin, folded sheets of polystyrene usually measuring less than a half-inch thick. It is engineered primarily to create a flat, uniform surface over old siding before installing new vinyl panels. Because it is so thin, it provides only a minimal bump in thermal resistance.
• Foam Board Delivers Maximum Thermal Performance: Rigid foam board insulation comes in thick panels that drastically reduce energy loss by stopping thermal bridging completely. It seals the entire exterior frame of the house in a continuous layer of high R-value protection. This material works best during major renovations where maximizing climate control is the primary goal.
• Combining House Wrap and Rigid Foam Prevents Rot: Installing rigid foam board over a high-quality house wrap provides the ultimate combination of insulation and moisture protection. The wrap stops trapped water from touching the wood, while the outer foam panels block heavy winter drafts. Skipping the house wrap can trap damp air behind the dense foam panels.
• Fanfold Offers the Most Budget Friendly Solution: Fanfold materials cost significantly less than thick rigid foam boards and require much less labor to install over large surfaces. It allows contractors to upgrade the exterior wall flat line quickly without the heavy expense of thick insulation. It is the best choice when leveling walls matters more than insulation performance.

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