The Macon Telegraph
Home Hunter - North
August 18, 1999

Just What Are Structural Insulated Panels?
by John Ricketson

Generally speaking, structural insulated panels (or SIPs , as they are usually called) are composed of a continuous core of rigid foam insulation which is laminated between two layers, (or skins) of a structural sheathing to form a single, solid building panel. You could compare the resulting strength to that of an I-beam, with the sheathing functioning as the flanges and the foam core acting as the web. The bottom line is that of a simple and very efficient structural system that provides much better thermal performance and substantially superior strength than conventional stick-frame construction offers.

The first insulated panel structure was built in the 1930’s by the USDA Forest Products Lab and in the late 1950’s the National Association of Home Builders used SIPs in their demonstration research homes. With many years of low energy costs, abundant labor, subsidized lumber, casual construction schedules, and high profit margins…….there was not much incentive for builders to use SIPs. Now, all that has changed and the advantages offered by structural panels address all of those issues much better than framed walls which are made up of approximately 20% solid wood. SIPs, on the other hand, are composed of about 2% solid wood and can be pre-cut before delivery to the building site with the waste being recycled right at the manufacturing plant.

Structural Insulated Panels are built in sizes ranging from 4 feet by 8 feet all the way up to 8 feet by 24 feet. These are one piece with no seams in the sheathing, you can imagine the decreased air infiltration due to just a few places where the panels are joined together. At these connections, the foam core is bonded to the other foam core with an expanding sealant and no interruptions in the insulation blanket around the entire building as compared to an insulation interruption and thermal bridging problem every 14-1/2 inches around a stick built home!

There are two main types of foam cores available, the beauty of both of these are that the insulating value is stable, meaning that it does not decrease with age as is the case with fiberglass and other loose fill insulation materials due to moisture accumulation, dust infiltration, and settling. Expanded Polystyrene (or EPS) is very inexpensive, easy to work with and yields a stable R-value of about 4.1 per inch giving the thinnest panel made a total insulating value of R=16 which is quite impressive compared to the average aged R-value of a 2x4 insulated stud wall being in the R=9 range. The other type of foam core is polyisocyanurate, a type of urethane foam developed for NASA when they needed a very high R-value per inch of installed insulation for space travel and a high resistance to flame spread for safety. Panels of this type are available up to R=38 with a total wall or roof thickness of only 5-1/2"

John Ricketson
Project Manager
120 Carriage Drive, Macon, GA  31210
(877) 662-6135 Toll Free
(478) 474-9370 or FAX (478) 477-6535


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