Structurally Insulated Panels

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Structurally Insulated Panels - SIPs

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SIP panels can create a highly thermally insulated and tight home envelopes. SIPs can be used for both residential and for commercial building.

The key to high thermal efficiency of a SIP is the thick foam core that is sandwiched between two layers of oriented strand board (OSB). This core is either made of EPS (expanded polystyrene), XPS (extruded polystyrene) or polyurethane. High thermal properties of foam core come from a closed cell structure that has a higher insulating value per inch then fiberglass insulation, which is an open cell structure. Rigid foam core in SIPs is also a solid and continuous layer that fills the wall cavity completely unlike fiberglass that is air permeable and prone to installation flaws that can lead to thermal losses due to convection loops in stud bays.

Since there are no studs in the wall, SIPs do not have a problem with thermal bridges which decrease thermal efficiency. SIPs are considered Green since the materials used in their manufacture are natural and non-toxic. EPS foam does not contain any Formaldehyde or C.F.C's while OSB sheeting uses less wood for a given wall then the frame build house. Also, about 95% of the tree is used to create wood chips for the OSB, where in case of solid timber we can use only about 60%. OSBs usually contain softwoods, such as poplar and aspen which are fast growing and harvested on a tree farm when young.

SIPs are made in factories and therefore handled in the safe, dry and climate controlled environment with minimal material waste. The panels are made straighter, stronger and greener providing many benefits for the builders and home owners. Once the panels are assembled, only minimal waste is left on the site, usually support blocks and straps that are used during transportation.

In terms of insulating properties, the common knowledge is that SIPs filled with EPS (expanded polystyrene) have R-value of 3.5 per inch. XPS (extruded polystyrene) reaches R-value of 5 per inch. Finally, polyurethane has closed cells filled with one of the thermally low conductive gasses (usually one of CFCs or HFCFCs thus not being very green) which are inert enough to give this insulation an R-value of 7-8 per inch.

Tech Talk!

What is U-Value?

Measure of material's heat-conducting properties: Heat conduction rate per unit surface area per unit temperature difference between its two sides.

How do I convert U-Value from SI units to English units?

Divide the SI number by 5.678. For example, If U=1.4 W/m²K in SI units, then 1.4/5.678 = 0.246 Btu/hr-sf-°F in English units.

Conversely to convert from English to SI, multiply by 5.678: 0.246*5.678 = 1.4 W/m²K.

What is R-Value?

R = 1/U-Value

A measure of the capacity of a material, such as insulation, to impede heat flow, with increasing values indicating a greater capacity

I have seen SIP manufacturers make comparisons between SIPs and traditional stick built walls with fiberglass insulation. Depending on the thickness of the wall, some values that are being advertised show, for example that a 4.5" thick wall (as a system) can achieve R-values of ~15 in case of EPS core and R-value of ~19 with XPS core. For thicker walls (6.5" and 8.25") there values go up to R-29 and R-37 for XPS core respectively.

Building with SIPs is a fast process. One does not need any especially skilled labor to assemble the outer envelope of the house and the time needed for assembly can be up to 5 times faster then with traditionally stud-framed method. Light crane is used to assist the crew in lifting and holding panels while they are fastened to each other.

SIP house made of SIP panels

One can find many types of panels on the market today according to their specific purpose. There are structural panels that are used for walls and roofs. Structural panels can also be clad with drywall on the inside to expedite finishing of interior spaces. There are also non-structural types that are used for internal non-load bearing walls or for external sheeting and insulation applications.

Structural SIP panel Drywall clad SIP panel

Structural panel Dry wall clad

Non-structral insulated wall panel Nail base wall insulated wall panel

Non-structural panel Nail base wall

I would say that building with SIPs would make for a stronger, more energy efficient, quieter and draft free home. I would rank high on the list of preferred materials if built my next energy efficient home today.

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