Structural Insulated Panels at Carlisle

These foam-core panels at Carlisle will stand for a century and keep heating costs down
By Roseann Henry of This Old House TV

The news photos of Hurricane Charley’s impact on Florida made a lot of people wonder just how strong their own homes are. We don’t get a lot of hurricanes around Boston, although they do sometimes take their last gasp up here after the worst is over down south. We get our share of other storms, though, including some wicked nor’easters. And we think about building strength all the time anyway, since we want the houses we work on to still be standing 100 years or more from now, no matter what kinds of storms roar through.

Strength is one of the biggest arguments in favor of panel construction over traditional wood framing. In panel construction, beams and studs are replaced by structural insulated panels, or SIPs, which consist of a foam core sandwiched between layers of oriented strand board. We’ll admit that we’re traditionalists and, yes, we like to frame the old-fashioned way. But when you hear about panel buildings surviving hurricanes and earthquakes while their traditionally framed neighbors shatter into sticks, you have to take notice.

“SIPs are at least three times stronger than traditional wood frame construction,” says Frank Baker, president of Insulspan, which manufactures the panels we used on the Carlisle Project. “In some cases SIPs can be up to ten times stronger. For example, after the Kobe earthquake in Japan there were documented instances of SIP structures left standing intact surrounded by the rubble of non-SIP buildings.”

We’ve also been taking notice of the price of oil, which makes a second argument in favor of SIP construction. “Long after our SUV craze is over, we’ll be dealing with energy efficiency issues,” says Jim LeRoy, president of Panel Pros, the company that installed the Insulspan panels at Carlisle. “The roof panels are eight and a quarter inches thick, with an R value of 32. The walls are six and a half inches thick, with an R value of 25.” That kind of top-to-bottom insulation will translate directly into lower fuel bills for this energy-efficient house.
July 16, 2004: I-joist floor panels form a blank slate on which to build the new ell connecting farmhouse to barn.

General contractor Tom Silva notes that the R values of individual panels are only part of the story. “The real benefit of SIPs is that there’s no break in the insulation,” he says. “In typical framing there’s a stud every 16 inches in the wall, and the R value of a stud is lower than the R value of the insulated walls beside them. You add up all the studs in a wall, and that lowers the R value of the wall overall.”

Baker agrees. “With SIPs there’s nothing given up to framing members, just a spline every 24 feet as opposed to a stud every 16 inches, and there’s none of the lumber around windows and doors. The difference in performance is really dramatic. With gas headed for $50 a barrel and natural gas going up even more, that’s going to be a bigger and bigger issue.”

Panel construction isn’t a new technology, but the oil embargo of the 1970s gave the industry a boost, and by 2002 there were more than 12,000 new homes a year being built with SIPs. As August 2004 drew to a close, we were pleased to count the new ell and master bedroom extension at Carlisle among this year’s SIP totals. We used panels for the new barn floor, too, taking advantage of their superior strength to span its wide distance. Baker says that’s not an unheard-of use of his panels, which are more typically used for walls and roofs.

“We’ve seen our panels used as flooring when there’s a need for insulated floors—where you have living space over an unheated garage, for example, or in coastal regions, where homes may be built on piers,” he says. “And we’ve seen them used in applications like the barn at Carlisle, where they can span greater distances than you could cover with traditional framing.” Tom notes that the 40-foot-wide floor in the barn is supported by a trio of LVL (laminated veneer lumber) beams and support columns every 12 feet in the garage underneath.

Structural insulated panels (SIPs) consist of two layers of oriented strand board (OSB) sandwiching a layer of insulation.

Both Baker and LeRoy note that the construction industry is plagued with a dwindling supply of craftsmen, and experienced framers are getting harder and harder to come by.
The ability to assemble the panels in a controlled factory setting, then erect them on site as complete walls, reduces the need for framers at the job site. And less time in the field speeds up the job overall without compromising quality—always a plus.

“It took about nine days in the field to install the SIPs,” says Tom, “plus another day and a half or so to make the connections to the old house. When you add in the three days or so it took to fabricate the panels, we could have framed the house in about the same time. But those first few days were in the shop, which frees up the job site for other work. And once the walls are up, they’re already insulated, which saves us those days. I definitely see time saved on work days on the site.”

As if we needed another reason to be sold on SIPs, Baker points out that the panels are made from renewable resources, with wood grown and harvested for just this purpose. “These panels eliminate an enormous amount of lumber from a project,” he says. “And they use absolutely no old-growth timber, which is getting more and more scarce.”
Strong, efficient, fast—and green? What more could you ask for in a house? And the first time a New England blizzard buries the finished house under a pile of snow, we’ll be glad to think about the homeowners warm and safe inside.

August 6, 2004: The ell is just about complete, with fully insulated walls and roof in position, with cutouts ready to receive windows and doors.