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Green Basics

Structural Insulated Panels

SIPs Provide Structure, Insulation, and Sheathing in One Package

A well-established building system

SIPs have a long history in the U.S. housing industry. Early versions were developed in the mid ’30s at the Forest Products Laboratory, and the first foam-core panel was produced more than a half century ago. SIPs have never quite broken into the housing mainstream, but they offer a number of advantages over conventional stick framing.

SIP construction is more expensive than standard frame construction, but because the resulting building envelope is tighter and insulation values potentially higher, using them may make it possible to downsize heating and cooling equipment. Lower operating costs over the life of the building should mean a net gain over conventional construction.

Most panels have foam cores

Expanded polystyrene.

By far the most common type of foam used in panels, expanded polystyrene (EPS) has an R-value of 3.6 per inch. Its low melting point is an advantage to builders who need to make field alterations with heated cutting tools. It has a fairly high perm rating of 3. EPS is the least expensive option.

Polyurethane and polyisocyanurate.

Nearly identical chemically, these foams have an R-value of about 6 or 7 per inch. They are more expensive and somewhat less widely available than EPS. Their higher melting point means that recesses for wiring and boxes must be drilled or routed instead of cut with a heated tool. They have a perm rating of 1, making them effective vapor barriers.

Extruded polystyrene.

At least three manufacturers make extruded polystyrene (XPS) panels. The foam is more expensive than EPS but has an R-value of 5 per inch and a perm rating of 1. It also has a high melting point. The companies are Foard Panel of New Hampshire, Murus of Pennsylvania, and Green Mountain Panel of Vermont.

Wheat and rice straw. At least one manufacturer now produces an SIP product…

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4 Comments

  1. Adam Stoddard | | #1

    Single Manufacturer?
    Murus also manufactures XPS panels contrary to what Foard panel claims.

  2. User avater GBA Editor
    Martin Holladay | | #2

    Response to Adam Stoddard
    Adam,
    Thanks for the information. I have updated the article to include Murus.

  3. User avater
    Ethan ; Climate Zone 5A ; ~6000HDD | | #3

    Has anyone used Agriboard?
    I'm interested in this product, but always wary of a one-supplier material.

  4. User avater GBA Editor
    Martin Holladay | | #4

    Response to Ethan T
    Ethan,
    Like you, I'm interested in hearing from any GBA readers who have used Agriboard.

    In general, it only makes sense to use SIPs if your building site is located near a SIP factory. The farther away from the SIP factory you are located, the less SIPs make sense (because trucking costs add up, and the fuel used for trucking undermines the environmental advantages that you are probably seeking).

    -- Martin Holladay

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