A Pretty Good House in Southern California
Big Bear Lake, CA
Location: Big Bear Lake, CA
Living Space : 2258 sqf
Cost (USD/sq. ft.): $107/sqf
Cost per square foot excludes the PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. system and all soft costs, and includes the 286-square-foot garage.
Foundation: Perimeter frost walls and slab on grade.
Foundation insulation: Horizontal layer of 6-in. EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest. under slab (R-25), with 2 in. of vertical EPS (R-8) at slab perimeter.
Above-grade walls: Double-stud walls (total thickness, 9 in.) with OSB sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. .
Above-grade wall insulation: 3.5 inches of open-cell spray foam and 5.5 inches of mineral wool (totaling R-34)
Siding: Fiber-cement and stone veneer.
Roof construction: Raised-heel scissors trusses, OSB sheathing, asphalt shingles.
Roof insulation: 18 in. (R-60) of blown-in cellulose.
Windows: Pella 350 windows with triple glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill.; U-factors range from 0.18 to 0.26.
Domestic hot water: Navien 199,000 BTUBritish thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature—about the heat content of one wooden kitchen match. One Btu is equivalent to 0.293 watt-hours or 1,055 joules. gas-fired condensing tankless water heater (Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners., 0.97 EF(EF). Efficiency measure for rating the energy performance of dishwashers, clothes washers, water heaters, and certain other appliances. The higher the energy factor, the greater the efficiency. In some appliances EF reflects the percentage of energy going into the appliance that is turned into useful energy.).
Mechanical ventilation: Exhaust-only system complying with ASHRAE 62.2A standard for residential mechanical ventilation systems established by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. Among other requirements, the standard requires a home to have a mechanical ventilation system capable of ventilating at a rate of 1 cfm for every 100 square feet of occupiable space plus 7.5 cfm per occupant..
Space heating: Two 12,000 BTU/h Mitsubishi Mr. Slim Hyperheat ductless minisplits.
Fire safety: Residential fire sprinkler system, all windows have tempered glass, non-ember admitting attic vents, fire-resistant exterior materials.
Blower door test results: 1.8 ach50
HERS Index: 53 (without PV), based on California’s 2008 Title 24 Energy Code (in effect until July 2014).
Photovoltaic system rated at 5 kW.
100% LEDLight-emitting diode. Illumination technology that produces light by running electrical current through a semiconductor diode. LED lamps are much longer lasting and much more energy efficient than incandescent lamps; unlike fluorescent lamps, LED lamps do not contain mercury and can be readily dimmed. lighting (except for 2 accent fixtures)
Low-flow water fixtures, 1.28 GPFGallons per flush. Measurement of water use in toilets. Since 1992, toilets sold in the United States have been restricted to 1.6 gpf or less. The standard for high-efficiency toilets (HETs) is 1.28 gpf. toilets, no outside irrigation system (100% native landscaping + gravel).
Indoor Air Quality
All paints and adhesives are low-VOC.
All furniture and cabinets are formaldehyde-free.
No carpeting; the upstairs flooring is wood laminate and downstairs flooring is tile.
A high-performance design for the mountains above Los Angeles
A few years into the housing bust, I started shopping around for a cabin to use as a getaway and vacation rental. I live in San Diego and I set my sights on the resort town of Big Bear Lake, in the San Bernardino mountains northeast of Los Angeles. Just 2½ hours away, it was a place where my family and I had spent many weekends skiing, snowboarding, mountain biking, and fishing.
During a leisurely on-and-off property search, I found several deals, but was generally underwhelmed by the quality of the housing stock from an energy perspective. Even the newer homes were of “barely legal” code minimum construction, and winter heating bills north of $500 per month were not unusual.
This was shocking to me, perhaps because my own mild coastal climate has a meager 1,200 heating degree days (HDDThe difference between the 24-hour average (daily) temperature and the base temperature for one year for each day that the average is below the base temperature. For heating degree days, the base is usually 65 degrees Fahrenheit. For example, if the average temperature for December 1, 2001 was 30 degrees Fahrenheit, then the number of heating degrees for that day was 35.) and 1,000 cooling degree days (CDD) per year. I typically use my furnace intermittently for a few months a year, and I don’t even own an air conditioner. Or maybe my expectations were just too high because my only exposure to cold climate construction came from reading Green Building Advisor!
Eventually, I started exploring the idea of building a house, but I soon learned that the going rate for new custom home construction (about $250 per square foot) was out of my price range. Things changed when I discovered several GBAGreenBuildingAdvisor.com articles about cost-effective, energy-efficient construction – most notably PostGreen’s 100K house, Eric Thomas’s house in Seattle, and Carter Scott’s work in Massachusetts. These case studies inspired me to pursue the project as owner/builder.
Outdoor temperatures can drop below zero
In the summer of 2013, I found a great deal on a bank-owned 50 ft. x 100 ft. lot with decent southern exposure, and set about designing the house. At this point my goal was to create a “Pretty Good House” that hopefully approached net zeroProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. Calculating net-zero energy can be difficult, particularly in grid-tied renewable energy systems, because of transmission losses in power lines and other considerations. energy use.
At an elevation of 6,800 feet, Big Bear has an alpine climate with 6,600 HDD and a Manual J design temperatureReasonably expected minimum (or maximum) temperature for a particular area; used to size heating and cooling equipment. Often, design temperatures are further defined as the X% temperature, meaning that it is the temperature that is exceeded X% of the time (for example, the 1% design temperature is that temperature that is exceeded, on average, 1% of the time, or 87.6 hours of the year). of -7°F. Yet it also boasts over 300 sunny days a year, and is even home to a solar observatory constructed by CalTech in 1969.
I eventually settled on a simple rectangular two-story shape, sandwiched between a huge oak in the front of the property and a small stand of pines in the rear. The design featured 2,200 square feet of conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. , with 3 bedrooms, a loft, 2½ bathrooms, and an attached one-car garage.
After performing some heat load calculations, I was confident that two minisplits could meet the heating demand, assuming a “pretty good” level of insulation and decent air sealing. With the help of a local architectural engineer, I soon had a minimal set of plans approved by the city.
“I never heard of that”
One of my biggest challenges (in addition to my own lack of time, experience, and money) was finding subcontractors and materials to implement the energy-efficient aspects of the design. For example, after weeks of calling around, I was unable to locate a company that could blow dense-packed cellulose into the framed walls. I guess in the land of R-13 walls, there isn't much demand for these installations.
Finding a dealer of high-density below-grade EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest. was an arduous task. But after working with a manufacturer's rep, I was able to find a local building supply company that special ordered it for me.
My framing sub was excellent and open-minded. I tracked down Rob after reading about his involvement in the construction of a local SIP(SIP) Building panel usually made of oriented strand board (OSB) skins surrounding a core of expanded polystyrene (EPS) foam insulation. SIPs can be erected very quickly with a crane to create an energy-efficient, sturdy home. house. But his crew had never heard of building gaskets, Zip sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. , blower door tests, double-stud walls, or textured housewrap. In Southern California, this would have been the case with any contractor, except for a few specialty builders.
So at every step of the design process I had to balance what I wanted to do with what materials and services were readily available.
Stemwalls and a slab on grade
My foundation consists of 3-foot-deep frost walls and a 4-inch slab on grade. The slab was insulated with a 6-inch layer of horizontal Type II EPS on a 6-inch-deep gravel bed, with 2 inches of vertical EPS at the perimeter between the frost walls and the slab. A layer of polyethylene was laid over the EPS before the slab was poured.
Even though my foundation contractor had never built an insulated slab before, the process was straightforward and he had no trouble pulling it off. However, I decided to take an angle grinder and smooth down the tops of the frost walls, so that my sill gaskets (from Conservation Technologies) would have a relatively smooth surface to rest on.
Double stud walls
My exterior walls were of double stud construction – an outer load-bearing 2x4 wall supporting TJI floor joists, and an inner 2x4 wall. The 2-inch gap between the two rows of studs created a 9-inch-thick wall.
Although most of the precipitation in this climate is in the form of snow rather than rain, I wanted to design my walls so that they could dry out to the exterior and interior. The walls were sheathed with OSB. James Hardie Plank siding was installed over a textured housewrap (Benjamin Obdyke's HydroGap).
To create an air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both., I installed 3.5 inches of open-cell spray foam on the interior side of the wall sheathing. Building gaskets and caulk completed the air barrier.
Between the two rows of studs we installed a 2-inch layer of continuous rock wool (CertainTeed Thermafiber). This was followed by 3.5 inches of rock wool in the inner wall stud bays (Roxul Comfort Batt). CertainTeed MemBrain (a “smart” vapor retarder) was installed on the interior side of the studs prior to drywall.
The roof was built with scissor trusses featuring 24-inch raised “energy” heels, 4/12 top chords, and 2/12 bottom chords.
The ceiling air barrier was a continuous sheet of taped polyethylene installed on the underside of the bottom chord of the roof trusses. The polyethylene extended to the top plateIn wood-frame construction, the framing member that forms the top of a wall. In advanced framing, a single top plate is often used in place of the more typical double top plate. of the outer wall, where it was sealed with staples and acoustical sealant. I had only a handful of second-floor ceiling penetrations.
The ceiling is insulated with 18 inches of loose-fill cellulose.
After agonizing over windows for months, I finally settled on Pella 350 vinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate). windows with triple-pane air-filled glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill.. The whole-window U-factors ranged from 0.26 to 0.18. To help capture passive heat in the winter, the windows on the south elevation had a SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. of 0.50.
I used a mixture of fixed, awning, and sliding windows. My entry doors were Masonite brand with U-factors ranging from 0.15 to 0.23.
The house has an exhaust-only ventilation system using an inline fan system purchased from Conservation Technologies. The fan has a maximum power draw of 38 watts (4.5 cfm/watt at 0.25 static pressure).
The exhaust air is pulled from three bathroom grilles that operate at a constant flow rate of 16 cfm each. However, each grille is equipped with a motion and humidity sensor that can signal the fan and boost airflow to 50 cfm at each location.
Two minisplits for heating
I calculated that my steady-state heat loss at -7°F (the Manual J outdoor design temperature) is about 20,000 BTUBritish thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature—about the heat content of one wooden kitchen match. One Btu is equivalent to 0.293 watt-hours or 1,055 joules. /h. So if it ever did get that cold (it never came close this season), my two 12,000 BTU/h Mitsubishi Mr. Slim minisplit units could keep up without much of a problem. Both are Hyper Heat units (indoor MSZ-FH15NA, outdoor MUZ-FH15NA) which can operate at full capacity down to 5°F, and drop to 80% of their rated capacity at -13°F.
The downstairs unit is on a RedLink thermostat than can be controlled with a smartphone app, and that unit alone should be able to heat the entire house most of the year. I plan to use the upstairs unit seasonally, during the worst months of winter.
I also installed an 18,000 BTU/h direct-vent gas fireplace as a backup heat source. The local electric utility, Bear Valley Electric, is known to suffer occasional outages in the winter, and the fireplace has a battery backup ignition system.
I took several measures to achieve better indoor air quality than a code-minimum house. Both of the home's combustion appliances (a tankless water heater and a fireplace) are sealed-combustion units, with all of the combustion air coming from the exterior.
My clothes dryer and other appliances, including the induction cooktop, are all electric. All paints and adhesives are low-VOCVolatile organic compound. An organic compound that evaporates readily into the atmosphere; as defined by the U.S. Environmental Protection Agency, VOCs are organic compounds that volatize and then become involved in photochemical smog production., and all furniture and cabinets are formaldehydeChemical found in many building products; most binders used for manufactured wood products are formaldehyde compounds. Reclassified by the United Nations International Agency for Research on Cancer (IARC) in 2004 as a “known human carcinogen."-free, which is a requirement of California’s “CalGreen” code. I also used no carpeting: the upstairs flooring is wood laminate and downstairs flooring is tile.
A 5-kW photovoltaic system
My solar array is composed of eighteen 280-watt American-made SolarWorld PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. modules, for a total system size of 5.04 kW. The PV array is connected to the electrical grid, and the local utility offers net meteringArrangement through which a homeowner who produces electricity using photovoltaics or wind power can sell excess electricity back to the utility company, running the electric meter backwards..
My hopes of achieving net zero energy use dwindled after a shading analysis downgraded my system’s expected performance to about 5,500 kWh per year. I expect that my minisplits will use 3,700 kWh per year, and everything else will come in at around 3,000 kWh. And that is not even including my natural gas usage. So the PV system will reduce, but not eliminate, the home's energy bills.
However, because the house is not fully occupied — it is a vacation rental — my net metering calculations show a huge surplus. In each of the last 6 months I have only had to pay the minimum electrical bill ($6), and I still have 1,800 kWh “in the bank”. March 2016 was a particularly encouraging month. With the thermostat set at 69°F for the entire month, my total electrical usage was 477 kWh, and the PV system generated 467 kWh. My gas bill averages $20. So while the house would most likely not operate at net zero under normal occupancy, I did end up with a rental property with very low utility bills.
About $107 per square foot before PV
I'm pleased with the house. It looks great and has stayed toasty during the worst months of winter. So far, all of my rental guests have enjoyed the house and found it comfortable.
I was able to keep construction costs down by being the general contractor and micromanaging all of the energy-efficient details surrounding the construction. I also did a lot of the interior finish work myself, about 6 weeks of labor in total over a period of a year or so.
Not including my own labor or the PV system, I spent about $107 per square foot in hard costs for the house and garage.
Exhaust fans. Although I think the constant pressure exhaust-only fan from Conservation Technologies is a very elegant system, if I did it over again, I would go with something simpler like Panasonic WhisperQuiet exhaust fans in each bathroom. The Conservation Technologies fan required a lot of ducting and is not as quiet as I had hoped. Although it is rated at only 55 decibels, I had to really work on isolating the fan from the mounting and the ducting to get the noise to where it was barely noticeable through an insulated wall. But I think a bigger issue with the fan is that it is such a specialized product, what happens when it needs to be serviced or replaced? If I had used standard bath fans, that would not be an issue. I doubt any HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. companies in Big Bear would touch my “crazy” inline Swedish fan system.
Mysterious air leaks. My air leakage rate (1.8 ach50) came in a lot higher than I had hoped for. At some point I would love to do some follow-up testing to try to figure out where the leakage points are. I don’t think that the air leakage has impacted my performance very much, since I am using an exhaust-only ventilationMechanical ventilation system in which one or more fans are used to exhaust air from a house and make-up air is supplied passively. Exhaust-only ventilation creates slight depressurization of the home; its impact on vented gas appliances should be considered. system that (hopefully) results in a negatively pressured interior with very little infiltration. I suspect that there are leaks at my sliding windows and my sliding glass door, as these are generally more leaky than awning windows. Another factor is the number of exterior doors; I have four but I probably could have made the house work with two.
I should have specified Zip sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. . Another thing I would have changed is my air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. and insulation choices. Seeing all the trimmed-off foam being packed up in trash bags and hauled away seemed like a sickening waste. I would have been better off using Zip sheathing as my air barrier, and some kind of cellulose (I have since found a contractor who installs damp-spray cellulose) or 100% rock wool as my wall insulation.
I should have included energy monitoring equipment. I wish I had invested in a simple energy monitoring system. I am looking to install one before next winter, so I can at least track the energy use of my minisplits.
Minisplits are fairly quiet, but have some noticeable sound. The minisplit indoor units are extremely quiet and unassuming. The outside fan coils are also very quiet, if you are standing right next to them. But because my exterior units were hung on the exterior wall, I do notice some sound vibrations through the wall when the exterior units are really working. So I can see the wisdom of mounting the exterior units on a concrete pad not attached to the house.
Stu Turner, M.S. Architecture, is an occasional environmental science T.A. at the NewSchool of Architecture + Design. He is also a member of the residential committee of the San Diego chapter of the USGBCUnited States Green Building Council (USGBC). Organization devoted to promoting and certifying green buildings. USGBC created the LEED rating systems..
- Stu Turner
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