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Bringing Energy-Efficient Construction into the Mainstream
By John Suppes and Bryan Osborn
From Title 24 to CALGreen, California is at the forefront of setting standards for energy-efficient home and commercial building construction. As with any new regulations, builders are naturally looking for solutions. The question: How will the green building push impact construction costs and profitability?
For nearly a decade, Palo Alto-based Clarum Homes has been committed to innovative construction technologies for high energy efficiency, healthy indoor air, comfortable living spaces and lower energy bills. Clarum's experience has shown that homes with these and other positive environmental attributes are more affordable than builders and homeowners may think.
Clarum is currently building two Northern California homes that demonstrate what is possible with energy-efficient construction and how it can be successfully applied in a range of home types.
Improved Energy Efficiency
While cutting-edge technologies and the latest gadgets get most of the attention in green building circles, builders already know the key to an energy-efficient home: build a tight, well-insulated envelope. The trick is doing that despite variations in floor plans, sites, climates, materials and crewmember capabilities.
Clarum has used Structural Insulated Panels (SIPs) in many of its homes to create high-performance building envelopes. With SIPs, it is much easier to reduce air leaks than with stick framing, since the panels are produced in a controlled setting and arrive at the jobsite in large, ready-to-install sections. The panels also have continuous insulation across their height, width and depth, along with fewer thermal bridges. The result is up to a 60 percent reduction in heating and cooling costs, plus healthier indoor air from sealing out dust, pollen and other irritants.
SIPs from Premier Building Systems figure prominently in Clarum’s two new developments. One custom home is under construction at The Enclave at Cypress Grove on the Monterey Peninsula at the Bayonet and Black Horse golf courses where 30 custom homes are planned. One custom home in Menlo Park will be built to stringent Passive House standards. Both projects were designed by architect Stuart Welte of Environmental Innovations in Design in Corte Madera, and exceed the CALGreen standards by a wide margin.
The Cypress Grove homes use SIP walls and roofs and are designed to be 50 percent to 60 percent more energy efficient than Title 24 requirements. These are custom homes but demonstrate that high energy efficiency can be achieved without taking extreme measures. Clarum plans to take the lessons learned from previous SIP projects and these homes and extend them into the production home environment.
Pushing the envelope on energy efficiency, the Menlo Park home is designed to meet Passive House standards, which target a 90 percent reduction in heating and cooling energy consumption -- with total energy savings of about 60 percent to 70 percent -- compared to typical building methods. The Passive House standards were developed in Germany in the mid-1990s and are starting to get more attention in the U.S.
Clarum’s Menlo Park Passive Home will be one of only a handful in California to meet the standard, and is believed to be the first certified Passive House residence in the Bay Area.
One thing that sets the Passive House standards apart from other green building programs is they are performance-based, rather than prescriptive. Instead of meeting the criteria on a checklist as with LEED for Homes and similar programs, project teams must demonstrate that specific goals have been met:
• An airtight building shell with less than 0.6 air changes per hour at 50 pascal pressure, measured by a blower-door test.
• Annual heating requirements less than 15 kWh/sq m/year (4.75 kBtu/sf/year).
• Primary energy use less than 120 kWh/sq m/year (38.1 kBtu/sf/year).
The Menlo Park Passive Home is a 3,300-square-foot, mid-level, single-story home with four bedrooms and 3.5 baths. To create the tight building envelope required under Passive House standards, the design calls for 6-inch-thick SIP walls (R-28) with 1.5-inch-thick Extruded Expanded Polystyrene (XEPS) foam “outsulation” added to the exterior, which also provides for continuous air migration adjacent to the OSB. The wall system provides a complete thermal envelope with no breaks.
The roof will be constructed using 12-inch thick SIPs (R-48). Other key elements for energy efficiency include no unconditioned spaces, double- and triple-glaze windows (down to U-21), insulated concrete slab, and clerestory windows to create a natural cooling effect.
For energy generation, the home will include photovoltaic panels and solar water heating. A Heat Recovery Ventilator (HRV) will recapture about 85 percent of indoor heat while providing fresh air at a rate of about 200 cfm and nine air changes per day. The HRV will operate almost continuously. When heating, the unit’s hydronic coil consumes only 60 watts of electricity on slow mode, which is comparable to a common hair dryer.
All told, it will be a net-zero energy home, also providing a more comfortable and consistent indoor temperature than standard homes. It includes energy-efficiency features that go beyond most current home designs, but that will likely become more common as homeowners and codes call for lower energy consumption.
Energy efficiency testing
The U.S. Department of Energy’s Oak Ridge National Laboratory has conducted blower door tests that show SIPs are 15 times more airtight than stick framing. The SIPs' structure had a leakage rate of only 8 cfm at 50 pascals compared to 121 cfm at 50 pascals for conventional wood framing.
SIPs also provide higher whole-wall R-values than stick construction. The lab evaluated entire wall assemblies, including heat transfer through studs and other structural members, at corners and joints, and around openings. For similar thickness walls, the SIPs were 47 percent better at resisting heat flow. A 3.5-inch-thick foam core SIP wall had a 14.09 R-value versus 9.58 R-value for 2x4 studs at 16 inches on center with fiberglass insulation.
The lab’s research showed that the SIPs even outperformed 2x6 studs at 24 inches on center, which had a 13.69 R-value. Clarum Homes’ own research also demonstrates SIPs’ energy-saving benefits. A case in point is a series of test homes built in Borrego Springs in conjunction with several partners under the DOE’s Building America Program (BAP). The SIPs helped contribute to a 61% whole-house energy savings compared to a BAP benchmark home.
SIPs component wall systems minimize waste, provide an extremely tight building envelope, provide a reduction in thermal bridging due to less studs, and offer very high R-values for the prescribed wall thicknesses.
The solution to achieving high energy-efficient homes exists right now. SIPs are really just a framing product used in conjunction with typical stick framing techniques. Builders typically use them in the exterior envelope only, and install them using splines and plates of nominal lumber sizes. In California, interior walls and floors normally are typical wood framing.
Because SIPs work in conjunction with established wood framing techniques, it takes very little training for experienced crews to master SIP installation.
With wood prices down from years past, SIPs are slightly more expensive compared to stick framing. However, this small increase in cost is only involving the exterior envelop. The immediate and long-term energy savings more than offset this cost difference for homeowners.
From a builder’s perspective, SIPs also install faster, helping reduce project cycle time and associated financing costs. Clarum, for example, anticipates being able to dry-in the Menlo Park Passive Home in only three weeks, helping save one month on the overall construction schedule.
The bottom line is that energy-efficient, durable construction doesn’t have to break the bank and there are an increasing number of project examples to learn from.
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Menlo Park Passive Home At-a-Glance
• 3,300 square feet; 4 bedrooms, 3.5 baths; single story
• 6-inch-thick SIP walls (R-28) with 1.5-inch XEPS “outsulation”
• 12-inch-thick SIP roof (R-48)
• Insulated concrete slab
• Heat Recovery Ventilator (HRV) with 85% heat recapture
• Clerestory windows for a natural cooling effect
• Photovoltaic panels and solar-heated water
Clarum Homes, Palo Alto
Environmental Innovations in Design, Corte Madera
Premier Building Systems, Dixon and Fife, Wash.
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John Suppes is the founder and President of Palo Alto-based Clarum Homes and Byldan Corporation, an early adopter of green building methods that has built more than 1,000 attractive and high-performance Enviro-Homes™ in Northern California. Find out more at www.clarum.com. Bryan Osborn is the Northern California and Hawaii sales representative for Premier Building Systems and is based in Sebastopol. Find out more at www.pbssips.com/bc.