The impressive thermal performance and R-values of this SIP home in Colorado resulted in significant energy savings and comfort.

After visiting Colorado on several vacations, Joan and Brian Moriarty knew they’d relocate from western Connecticut to build a timber frame home there. Timber frame construction fit in naturally with their desire to build a mountain home with an open floor plan for frequent entertaining of guests. What they didn’t know was how well their timber frame, wrapped in Structural Insulated Panels (SIPs), would perform in the cold winters and warm summers.

Their 3/4-acre lot, located at a 9,100-foot elevation overlooking the community, is perfect. The south-facing site takes advantage of the ample Colorado sun (which boasts an average of 69.67 percent sunshine1) for passive solar heating; only a few of the native aspen and lodgepole pine trees had to be cut to locate the house properly.

Brian Moriarty, an engineer, was impressed by the structural integrity of timber framing, but acknowledged “there is a certain artistry to timber framing – it’s not pure engineering.” As a result, they hired architect Karen Smuland to put their design ideas on paper. Smuland, never having worked on a timber frame before, bought books to become familiar with timber framing and structural insulated panels.

After interviewing several timber frame companies, Davis Frame Co. (Claremont, N.H.) was chosen to provide the exterior shell material, including the Douglas Fir timber frame, SIPs, and Loewen (Steinbach, Manitoba) windows and exterior doors.

The Moriartys, Smuland, Davis Frame President Jeff Davis, and builder Calvin Stewart of Alpine Concepts (Silverthorne, Colo.) had several meetings and conference calls to coordinate not only the architectural plans with the timber frame, but the details of putting up the timber frame and installing the SIPs with local timber framer Rich Hackett of Great Divide Builders. Stewart, who had only repaired old timber frame buildings, caught on quickly to the timber frame plans, likening the “grid packet” to the metal buildings he used to build.

Understanding SIPs

SIPs, first tested in 1935, have become more popular in the last decade as attention focuses on green building and energy efficiency. SIPs are prefabricated insulated structural elements used for building walls, ceilings, roofs and floors that replace conventional stud and batt construction.

Structural wall panels are an engineered “sandwich” or laminate filled with polyisocyanurate (called in “polyiso” or “urethane”), expanded-polystyrene (EPS), or extruded polystyrene (XPS) with structural facing or sheathing (usually OSB) on each side. Panels are either 4 or 8 feet wide, and come in lengths varying from 8 to 24 feet long in 2-foot increments.

“Urethane” or polyiso panels (polyisocyanurate) are made two ways. In one method, chemicals are simultaneously mixed together and inserted between two sheets of OSB. As the chemicals react, they expand and bond directly to the OSB. The other is to laminate pre-formed polyiso between the panel skins. External pressure is continuously applied to the panel, creating an ultra-dense closed cell panel with a Class 1 fire rating.

EPS and XPS panels (expanded-polystyrene and extruded polystyrene) are composed of continuous rigid foam insulation laminated between two layers of structural facing or sheathing with an adhesive. EPS and XPS panels have a lower R-value vs. the same size polyiso or “urethane” panel, but are less expensive and equally as efficient.

In general, R-values vary from R-15 to R-38, depending on the type, and thickness of panel used. The Oak Ridge National Laboratory (ORNL), a multi-program science and technology laboratory managed for the U.S. Department of Energy, set a new standard in calculating R-values when it completed a study on thermal performance and whole wall R-value comparison. Most R-values are calculated at “center of cavity,” a point in the wall’s cross-section containing the most insulation, or “clear wall,” the exterior wall area containing only insulation and necessary framing materials for a clear section with no fenestrations, corners or connections between other envelope elements such as roof, foundations and other walls.

Oak Ridge reports: “For builders and building owners to appreciate the added thermal benefits of many of the alternatives to conventional wood-frame wall construction, it is necessary to use a whole-wall R-value. The market focus on clear-wall or even worse center-of-cavity R-value, is misleading and inhibiting the market penetration of high-performance wall systems into the residential construction industry.”2

Oak Ridge compared a 6-inch EPS Structural Insulated Panel wall with a 2 by 4-inch and 2 by 6-inch stick and batt construction wall. In terms of whole wall thermal performance, the SIP wall significantly outperformed the conventional wall. Because SIPs are continuous wall systems, there are no breaks every 16 or 24 inches, which creates a superior thermal envelope.

ORNL’s advanced whole wall comparison method finds the other standard components in stick and batt construction can reduce R-values in as much as 30 percent of the wall area, while SIPs perform at approximately 97 percent of their stated R-value overall, losing only 3 percent to nail holes, seams, and splines. Even wiring chases that are precut or preformed into the foam core do not disrupt the continuous layer of insulation.

In addition to comparing whole wall R-values, ORNL also looked at interior wall surface temperatures of both a SIP wall and a stick and batt construction wall. The stick wall’s interior surface temperature dropped significantly at every stud connection, while the SIP wall remained consistent across the entire surface. Consistent interior temperatures translate into even, balanced comfort in the home. In addition to drafts and cold spots in the home, inconsistent wall temperatures cause “ghosting,” an accumulation of dust and soot in regular patterns on walls.

Tackling SIP Concerns

Concerns over the presence of formaldehyde in SIPs have been met head-on. The adhesives used in SIPs contain phenol formaldehyde. Paul Malko, a mechanical engineer at Foard Panel (West Chesterfield, N.H.), explains, “These adhesives have proven to be highly durable, water proof, and do not release significant amounts of formaldehyde like the urea formaldehyde that made people sick. The formaldehyde in OSB is phenol-formaldehyde, which has not shown the same health effects as urea-formaldehyde.”

The U.S. Department of Housing and Urban Development (HUD) has set a limit on formaldehyde levels in manufactured housing. While setting limits of 0.2 PPM in plywood products and 0.3 PPM in particleboard products, OSB has been exempted from the testing and certification because the formaldehyde limits are so low. While in general formaldehyde exposure does not cause health problems, limiting exposure to urea formaldehyde building products and phenolic resins can only help. “When compared to furniture, carpets, cabinetry, and many household wood finishing products, the SIPS are not a significant formaldehyde contributor to the indoor air. Because of this and many other factors it is critical to properly ventilate the home” Malko concludes. “This will reduce all indoor pollutants and create a healthier home.”

Some building contractors express concern over installing the wiring and plumbing in a panel home. Doug Anderson, sales manager at Winter Panel, Inc. (Brattleboro, Vt.), confirms this is the first question people ask about panels, and most are surprised at the simple solutions: “As far as running the electrical wires, there are several options. Some electricians simply push the wire through a horizontal wire chase pre-drilled into the foam core of the panel, while others make a vertical rout through the OSB from the outlet down to the floor level and push the wire in before the drywall is installed.”

Winter Panel’s R-25 urethane wall panels and R-38 roof panels were purchased for the Moriarty’s home. Winter Panel manufactures SIPs for commercial and residential construction designed to be energy efficient; the company’s OSB board is certified by the Sustainable Forestry Initiative.

An additional technique, according to Malko, “is to create a wire chase between the edge of the flooring and the wall that gets covered up later with baseboard trim. It is then easy to fish a wire from the electrical box to this chase.”

Plumbing is not a concern. “There are almost no differences between plumbing in a panel home and a conventionally-framed house. Plumbing runs should be kept in interior conventionally framed partition walls or in specially constructed plumbing chases,” Anderson says.

Thermal performance and R-value are only two of the benefits of using panels. Because the SIPs are installed and connected using splines and high expanding foam, the house is both framed and insulated at the same time and are installed within a matter of days, reducing labor costs and the materials’ exposure to the weather. Stewart says, “Before the tar paper and ice and water shield were in place, the roof didn’t leak — even during a rainstorm.”

In areas with high wind and snow loads, SIPs offer substantially greater strength than conventional construction, and can even protect the house from the elements. Stewart knows firsthand it’s common in Colorado to have ice dams on roofs, which are hard on the shingles (in fact he has one on his own conventional house) but, he notes, “the SIPs on Brian and Joan’s roof have prevented ice buildup, protecting the roof.” Additional information is available via “The Best Defense Against Ice Dams: Energy Efficient Roofs” at http://www.ornl.gov/sci/roofs+walls/articles/icedams/index.html.

SIPs also meet building codes and pass ASTM International standards for fire safety. Best of all to the homeowner, SIPs energy efficiency means reduced heating and cooling costs, as Brian and Joan Moriarty experience firsthand.

Moriarty Energy Savings

When the Moriartys compared heating costs with their neighbors in Colorado, they were pleased to discover huge savings. They report using 6.57 BTUs for heating and cooking.

According to the Structural Insulated Panel Association (SIPA), homeowners can cut energy costs by up to 50 percent. “Because SIPs create a tighter building envelope than conventional insulation, the size of heating and cooling equipment can be reduced. That reduced costs immediately,” says Bill Wachtler, executive director, SIPA. Most importantly, though, adds Wachtler, is that “SIPs keep your costs down from season to season, year after year.”

The Moriartys have already seen the benefit of their SIPs on their 4,200-square-foot home. At first when they heard their neighbors comparing heating costs, Brian and Joan Moriarty went back to check their bills because they were spending far less than any of their neighbors, some who live in timber frame homes, but with conventional batt insulation, not SIPs.

In 1997, the U.S. Department of Energy surveyed single-family homes using propane or natural gas in the Northeast, Midwest, and West. Moriarty’s usage of 6.57 BTUs (which includes cooking) is in the lowest 10th percentage. And when it comes to energy-efficiency, there’s always room for improvement.

Joan and Brian Moriarty sum it all up: “The degree of efficiency of our timber frame home is an unanticipated benefit which we are now appreciating. We knew it would be more efficient than stud-framed homes, but didn’t fully appreciate how much better it would be. We’re very happy with our choice!”

Stewart, too, was surprised at how low their energy bill was, adding, “It is definitely due to the panels in the roof and walls – and the fact that we sealed every joint with foam.”

Other Energy-Efficient Materials Used

Other materials contribute to the energy-efficiency of the Moriarty home, as well. After learning of the many benefits of the SIPs, the couple’s focus became the energy-efficiency of the home. Builder Calvin Stewart suggested an insulated concrete form (ICF) foundation system manufactured by Quad-Lock Building Systems (Surrey, B.C.), having seen excellent ICF performance in many of the conventional homes he’s built over the years.

In addition, Joan and Brian Moriarty chose ENERGY STAR Loewen Douglas Fir windows and doors, which consistently have excellent U-Value and design performance (DP) ratings. They also added Loewen’s HeatSmart windows casement, awning and custom triangle windows, as well as Loewen terrace doors in the great room and dining room to take advantage of their beautiful surroundings.