Net Zero Energy Simplified Using SIPs for a High-Performance Building Envelope
Want to build a net zero energy home? Forget about the solar panels; they come later—much later!
Now that I have your attention, let me clarify. I teach many classes on net zero construction through the National Association of Home Builders and other trade groups, and participants often come in assuming I’ll focus on renewable energy. But in many climate zones, you simply cannot install enough solar panels on a home to power all of its energy needs, unless you cut all the other loads first.
While on-site renewables like solar and wind certainly play a role in net zero and energy-positive homes, they come into play only after you’ve addressed a host of siting, materials, and equipment issues (see “Twelve Essential Steps to Net Zero”).
For this article I’ll highlight one of the most essential characteristics you will need to include in any ultra-energy-efficient home: a tight building envelope.
The Envelope, Please
While heating and cooling account for a lower share of total home energy use than they did historically, they still consume upward of half of a “normal” home’s energy. To optimize and reduce this energy load, it is crucial to ensure a tight, well-insulated building envelope.
A simple way to achieve this is with high-performance building materials such as structural insulated panels (SIPs) and insulating concrete forms (ICFs).
If you’re not familiar with them, SIPs are building panels consisting of a core of structural insulating foam sandwiched between two structural facings, typically a composite board such as oriented strand board (OSB). SIPs combine in one package the interior and exterior sheathing and the insulation.
In addition to providing continuous insulation throughout much of the structure, SIPs come in very large panels (up to 8 feet x 24 feet), leaving very few joints to seal. By sealing those joints very carefully, instead of losing up to 30% of your energy due to air leakage as you might with other building methods, you lose only 1% or 2%.
SIPs’ energy performance has been shown both in the lab and in real-world applications. In the lab, DOE’s Oak Ridge National Laboratory (ORNL) found that SIP structures are up to 15 times more airtight than stick-framed walls insulated with fiberglass batts. Its tests showed that a SIP structure leaked only 8 CFM50 compared to stick framing, which leaked 121 CFM50. For walls of a similar thickness, SIPs also were 47% better at resisting heat flow than stick framing. A 3-1/2-inch-thick foam core SIP wall had a 14.09 R-value, versus a 9.58 R-value for 2 × 4 studs at 16 inches on center (OC) with fiberglass insulation. The SIP structure’s 14.09 whole-wall R-value even outperformed the 13.69 R-value of advanced framing with 2 × 6 studs at 24 inches OC.
TWELVE ESSENTIAL STEPS TO NET ZERO
An ultra-energy-efficient home depends on twelve mutually reinforcing factors. In a climate dominated by heating days, these factors are
- Building orientation. The home’s ridge line needs to run east-west, so you have a south-facing roof slope for placing solar panels to power the house and for south-facing windows to capture sunlight in the winter.
- Simple design. Homes that are nearly square limit exterior surface area to reduce energy loss and minimize construction costs, thereby freeing up money for other energy-saving features.
- Window orientation. Placing most windows on the home’s south side captures solar energy and daylight in winter, and minimizes heat loss through north-facing windows. Appropriately sized overhangs help prevent excess solar heat gain in summer.
- Thermal mass. The correct thermal mass, such as thermal mass floors and countertops, is essential for storing solar heat during the day, and for heating the home at night.
- Tight building envelope. Limiting air leakage is crucial for energy efficiency. Systems such as SIPS help create an airtight house and have fewer joints to seal than other building methods, such as stick construction.
- Balanced insulation. Walls, windows, and roof all must have sufficient insulation for a highly energy-efficient home. Overinsulating the roof at the expense of the walls and windows is not cost-effective or energy wise.
- Balanced ventilation. In a tight home, ventilation is essential. The CFM of kitchen and bath exhaust fans should be balanced with the home’s air intake fans, which ensures sufficient fresh air without wasting energy.
- Heating and cooling equipment. Once you’ve got the envelope right, the next step is to install efficient heating and cooling equipment. Examples include ground source heat pumps and inverter-driven heat pumps.
- Domestic hot water. To reduce electricity and natural gas consumption, DHW can be provided by a ground source heat pump or solar panels.
- Efficient appliances. Energy Star is a good place to start, but be sure to review each appliance’s Energy Use statistics, and shop carefully for the lowest- consuming units, from kitchen to laundry room.
- Efficient lighting. The key to energy-efficient lighting is to remember that your goal is to is to light surfaces, such as countertops and work spaces, rather than lighting entire spaces. Light-emitting diodes are the most energy-efficient light option.
- Alternative energy. The first eleven steps must be done correctly to lower the home’s energy consumption to the point where all of it can be provided by on-site renewables, such as solar panels.
For more information, watch this video.
Today’s Neopor SIPs, with core insulation values of R-4.7 per inch, outperform the panels tested at Oak Ridge by another 21%, which would be the equivalent of adding R-5 foam sheathing on the outside of the advanced-framing wall. When you move up from 3.5 in core to 5.5 in core thicknesses, the Neopor SIPS are even more impressive, providing an R-29 wall assembly when drywall and siding are included in the calculations.
Case Study: Isler Residence
Lab testing helps show the superior performance of SIP-built envelopes. But more importantly, homeowners see tangible results in their homes.
One example is a home I built in Coupeville, Washington (see Table 1). Located in climate zone 4 Marine, the Isler residence was the 2013 DOE Challenge Home Winner for Housing Innovation.
Projected annual utility costs
Annual energy savings
Projected total annual energy cost savings (compared to 2006 IECC)
The 2,900 ft2, three-bedroom home on Washington’s Whidbey Island relies on SIPs as part of a comprehensive set of efficiency measures to achieve a HERS index of 34 (without solar PV). The walls are 5-5/8-inch-thick R-26 SIPs, the pitched roof is 9-3/8-inch- thick R-41 SIPs, and the flatter roof sections are 11-3/8-inch-thick R-50 SIPs. In a blower door test, the home achieved 1.32 ACH50.
While we building professionals care about these metrics to compare building methods, what matters to the homeowners is what they see on their utility bills. The 2013 projected annual energy cost savings without solar was $1,532, compared to a home built to the 2006 International Energy Conservation Code (IECC). Adding solar, the savings balloon to $2,850 per year—enough to afford a nice vacation every year!
The DOE studies mentioned in this article are available for download at “Heating and Blower Door Tests of the Rooms for the SIPA/Reiker Project,” Oak Ridge National Laboratory, March 15, 2002.
Get more information on the Isler home(PDF).
Learn more about Ted Clifton and Zero-Energy Plans, LLC.
Working with SIPs
Not only do SIPs help create a high-performance building envelope, but they’re also easy to build with. The large panel sizes allow you to set an entire wall, with the windows and doors pre-cut out at the factory, in just a few minutes.
To get started, I send the SIP manufacturer (Premier SIPs, Puyallup, Washington) my home plans, and it produces shop drawings showing the panel details—number and size. It then makes the panels in a controlled, indoor environment, and numbers each one to show where it goes in the home.
If you haven’t built with SIPs yourself, the learning curve is pretty short, as it’s pretty easy to set and attach the panels. Crews fasten the panels together with nails, screws, or staples, and special adhesives, using standard power tools. And as SIPs are presized to your specifications, cutting them is usually not necessary, although you can field trim them as needed to fit the foundation and other parts of the structure.
While home design and construction continues to evolve toward net zero energy homes, many of us are now pushing the envelope toward energy-positive homes. With a high-performance building envelope, energy-efficient equipment and lighting, other measures, and on-site renewable power generation, not only will your homeowner customers receive a check from the power company instead of sending one in, but they also will never have to stop at the gas pump again!
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