What Are Structural Insulated Panels (SIPs)?

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I designed and built a house in 1985 in northern New England. The carpenter I hired had been trained at the Shelter Institute in Maine, well known for post and beam construction. I chose this carpenter, because he had built a home similar to what I had designed – passive solar and super-insulated. When I went to see it, I practically hired him on the spot.

SIPs: what they are and what they do best

When I was writing about the construction of this house a couple years ago, I looked up the Shelter Institute. I discovered that, instead of framing with two layers of 2x4s, they are now using SIPs, Structural Insulated Panels. That was wonderful to see! SIPs offer excellent insulation, and construction goes much faster.

Instead of framing twice and insulating small spaces by hand, walls are built off-site and brought to the home to be installed. Door and window openings are cut at the factory. Electrical and HVAC channels are cut into the wall at the factory, too, making the finish work simple at the job site. What a breeze it must be to put up a Shelter Institute post and beam house now!

From the Structural Insulated Panel Association (SIPA) website:

Structural insulated panels (SIPs) are high performance building panels used in floors, walls, and roofs for residential and light commercial buildings. The panels are typically made by sandwiching a core of rigid foam plastic insulation between two structural skins of oriented strand board (OSB). Other skin material can be used for specific purposes. SIPs are manufactured under factory-controlled conditions and can be custom designed for each home. The result is a building system that is extremely strong, energy efficient and cost effective. Building with SIPs will save you time, money and labor.

Insulation, R-value and an air-tight envelope are the most important factors to reduce energy costs and increase comfort. SIPs provide all of these.

The R-value of a SIPs panel ranges from 14.4 – 58.3 depending on the insulating material and its thickness. Fiberglass batts range from 11 – 38 for the same range of thicknesses. Quite the difference!

SIPs, thermal bridging, and air infiltration

According to SIPA, SIPs out-perform fiberglass insulation and retain their R-value for the life of the home. They reduce thermal bridging and air infiltration, and fight off extreme temperatures. Thermal bridging is the transfer of air from a stud where it meets an exterior wall. Lumber is a poor insulator and acts as a bridge between the interior and exterior. SIPs also perform better in cold temperatures, because cold air can move through the air spaces of fiberglass.

Because a SIPs building envelope is air-tight, fresh air needs to be incorporated into it. A heat recovery ventilator (HRV) is installed to exchange indoor and outdoor air several times a day without affecting the heating or cooling of the space. There’s no need to crack a window for fresh air and lose your heat, thereby wasting energy.

SIPs, energy efficiency, and savings

Because of the high R-value of SIPs and the airtight envelope it creates, a home’s energy needs can be reduced by as much as 50%. Besides that energy efficiency, SIPs are responsibly made. The rigid foam core uses minimal petroleum, because it is 98% air. The foam insulation is made using a non-CFC blowing agent.

I have used a lot of building materials over the years, but never SIPs. I have been in a SIPs home, and the feel is similar to strawbale – airtight with great acoustics. I think this is a green building material that needs to become more mainstream as fuel prices continue to rise.

SIP timelapse construction:

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Nan Fischer

Nan Fischer has been living and building green for over 35 years. Nan’s emphasis on the BuildDirect blog is about how to make your dollar stretch further, while also moving toward a more sustainable lifestyle, as well as upcoming and existing technology to help us live in an ecologically-friendly way. Nan also authors posts on the website of her seed business, sweetly seeds.