What makes a high-performing house?
By Chris Briley & Heather Chandler
THERE ARE A LOT of loosely defined terms used to describe how “green” a house is. Luckily, some professionals in our industry have worked very hard to find ways to quantify this almost intangible quality, and in so doing, have generated new nomenclature that can often sound foreign to those outside the industry.
Net Zero refers to the building’s energy consumption and means that the building produces as much energy as it consumes. This is achieved through the use of renewable energy systems, most likely in the form of photovoltaic solar panels. It is also very likely that the home’s energy demand has been reduced by increasing the building’s insulation, system performance, and air tightness values. If a home produces MORE than it uses, it is said to be Net Positive.
Net Zero Ready is a term that is applied to a home or building that has done everything necessary to become Net Zero except add the renewables. One might think that solar panels are the most important part of this equation, but in fact, it is the act of reducing the energy demand of the house that is far more critical. Skimping on insulation or air leakage, or reducing the performance of the windows, could mean one would need to double the amount of solar panels on the roof.
The term Passive House or Passivhaus (not to be confused with passive solar design which refers to a design strategy) is an international standard focusing on the building’s energy demand, or how much energy a house uses. A certified Passivhaus uses about 90% less energy than a typical code compliant house, meaning in essence that it can be heated in the dead of winter with the same amount of energy a single hair dryer consumes, or about the same amount of heat given off by a small dinner party. Impressive indeed!
When a home is EnergyStar certified, a series of energy modeling, inspections, and testing provide the completed home with a score on the HERS (Home Energy Rating System) index. The U.S. Department of Energy has determined that a typical, code-compliant, well-built home has a HERS score of 100. So if you hear of a house having a score of 80, that home uses only 80% of the energy of the typical home. The lower the score, the less energy it consumes. If a home has a score of 0, then it is a net zero home. A HERS score below zero means the house is net positive.
An energy efficient house is also a tight house, meaning that it has very few leaks where air can pass from the interior to the exterior (or vice versa). Air sealing is one of the most costeffective measures one can take to deliver high performance. This is achieved by careful planning of the construction details and also by vigilant building professionals armed with an assortment of tapes and sealants, who patch every hole and seam in their path.
But how is air tightness measured? A blower door test is performed by removing an entrance door and replacing it with a special door with a large fan in it that then depressurizes the house. It also measures the rate at which air flows into the house to replace the air being displaced by the fan. This metric is known as ACH50 (air changes per hour at 50 pascals of pressure). The lower the number, the better. The average home for sale has an ACH50 of 3.9; for new homes it’s 2.5. To be a passive house, however, a building must have an ACH50 of 0.6!
Of course, many homes do not seek certifications or third party verification, but they do implement many of the same strategies as those that do. Often their proof is evidenced in their low utility bills or in their ease of comfort on those brutal Maine winter nights. These homes fall into the category of Pretty Good House, a popular colloquial term.
The homes featured on the following pages all address sustainability and deliver high performance as compared to a typical home. Whether they pursue certification or not, a high performance home is one that implements the same strategies: they reduce energy demand by insulating; air-sealing; choosing well-insulated, climate appropriate windows; choosing efficient mechanical systems; balancing air ventilation; choosing efficient fixtures and appliances; and incorporating renewable energy systems if possible.
Every home has an impact on our environment: some great and some slight; some negative, some positive. A high performing home is one that is leading the building industry in a positive direction.
Editor’s Note: The submissions for homes featured in this article came from home owners, builders, architects and renewable energy professionals across the state. We reviewed data for the submissions received and selected the six homes that you will see featured in this issue. As you will see, they represent a diversity of size, style, geography, methodologies, price and performance, showcasing a variety of options for Maine homeowners.
Five of this year’s submissions are newly constructed properties and one is a re-build. In every case, energy and performance was a goal of the design and build from the start. For each project, you’ll find an overview of the home, a summary of what we like about it from a technical perspective, details about the approaches implemented in the house and the performance it has achieved.
New England farmhouse charm
AN APPAREL AND textile designer-turned developer, homeowner Patrice Miller cut her teeth developing the well-loved Matterhorn Ski Bar in Newry, Maine. Since then, she has developed four more projects and this house is the first of what is planned to be a small community of super-efficient solar homes in Cumberland—a vision inspired by those first passive solar projects in Newry and executed in tandem with Mottram Architecture. Inspired by vintage and architectural salvage pieces, Miller seeks to create homes that not only convey warmth in design but also maximize the energy and warmth provided by the sun.
The 1700 sf Cumberland house is currently operating Near Zero, with the intention to be Net Zero when a third row of solar panels is installed in the future. The 3-bedroom house is home to Patrice and her two children, with room to turn the basement or room above the garage into bonus space. The garage is wired for an electric car charging station in the future.
Miller believes that homes and the earth are sacred spaces and as such, they should be integrated. The home features natural materials, including pine floors, and low window sills allow sunshine to stream across the floor and minimize the boundary between home and outside world.
Why we like it: With this project, Mottram and Live Solar Maine had a strong focus on delivering a highly energy-efficient house, in a simple approachable aesthetic, for a highly marketable price. It is not easy to find a net zero ready home for $205/sq ft, much less one with such comfortable New England charm. The home’s simple structure are time tested vernacular forms and expertly combined with higher levels of insulation and tight construction.
EFFICIENCY: HERS score—10. Net Zero ready (20 panel solar array installed, net zero when the last 10 are installed later). It costs only $378/yr. for heat and electricity.
BUILDING ENVELOPE: Foundation—poured concrete with 4” of Extruded Polystyrene Foam. R-20. Walls—9.25” thick walls of dense packed cellulose insulation and 2” XPS strips at every stud bay as a thermal break. R-40. Roof—R-60 on flat ceiling and vaulted ceiling over master has 2×12 rafters padded with 2×4’s to create a 15” thick cavity packed with cellulose insulation to R-50. Windows—Double pane Low-E. Air Tightness—ACH50 – 1.5
SYSTEMS: Heating and Cooling—ductless mini-split heat pumps, wood stove back-up. Domestic Hot Water—heat pump water heater. Ventilation—exhaust only system; passive air intake portals and 3 bath vent fans.
RENEWABLES: 20 panel solar array
SIZE: 1726 sq ft with an attached 88 sq ft breezeway (Total 1814 sq ft) with an attached 26×24 garage
COST: $202/ sq ft
- DESIGNER: Live Solar Maine / Mottram Architecture
- BUILDER: Live Solar Maine
- RENEWABLES: Teel Green Energy
- ENERGY/PERFORMANCE CONSULTANT: Mottram Architecture
A “Pretty Good House”
AS MANY PEOPLE do when approaching retirement, the Sheehys decided it was time to downsize from their 4000 sf home. Not only was it no longer serving their needs, but the energy costs to run the house were as high as $6000 a year. They wanted a comfortable single level home that was easy to live in, low maintenance, and most of all, energy efficient.
The Sheehys had done a lot of research into high performance building practices, and while they respected the contribution that certifications such as LEED, Energy Star and Passive House brought to the market, they felt they could achieve similar results without the added expense of certification. So they chose to follow the Pretty Good House guidelines (see page 26), a model developed by a group of Maine building professionals in 2009 that seeks to find the sweet spot between price and performance in implementing energy efficient, high performing homes.
Working with Kaplan Thompson Architects, they utilized the Passive House Planning Package modeling software to compare the impacts that various design choices would have on the home’s energy use and cost. The result, a home that is airtight enough to test out at ACH50–0.59, a rating that qualifies for Passive House certification (though they have not pursued it). The house features Intus triple-pane windows and doors.
Why we like it: This Pretty Good House uses a clever double stud wall assembly with an interior air/vapor barrier membrane in the middle of the wall (but toward the interior where it is still on the warm side). This allows plumbers and electricians to make penetrations in the interior wall without compromising the air tightness of the home. It also delivers excellent energy efficiency.
EFFICIENCY: Near Net Zero. $337 annual estimated cost for heat.
BUILDING ENVELOPE: Slab—4” concrete over 4” of rigid EPS insulation R-20. Walls—Double stud walls with dense packed cellulose and batt insulation R-42. Roof—Truss system with loose fill cellulose R-70. Windows—Triple pane European tilt-turn. Airtightness—ACH50 – 0.59
SYSTEMS: Heating and Cooling—ductless mini-split heat pumps with additional radiant heat under bathroom tile. Ventilation—Zehnder ERV
RENEWABLES: 6.5kw solar array
SIZE: 1920 sq ft
COST: $242/ sq ft
- DESIGNER: Kaplan Thompson Architects
- BUILDER: Greenleaf Building
- RENEWABLES: Maine Energy Performance Solutions
- ENERGY/PERFORMANCE CONSULTANT: Kaplan Thompson Architects
Highly energy-efficient in a classic coastal neighborhood
South Portland, Maine
INSPIRED BY THEIR lovely coastal neighborhood in South Portland, the owners wanted to create a high performing home that matched the classic aesthetic of the surrounding area, rather than the boxy style that is common with many contemporary homes. The home needed to be large enough to accommodate the owners full time and their children who visit them often, along with a two-car garage.
Faced with a small buildable area and 26’ height limitation, the solution was to build a one and a half story home over a sunken garage. The result, a Net Zero Ready, cedar shingleclad beauty, adorned with natural stone and exposed rafters that looks like it belongs here.
The smart 3-bedroom home features 4” of foam under the basement slab, a thick double-stud wall assembly, and an energy recovery ventilator that works in tandem with the tightly sealed exterior envelope.
Why we like it: This home follows the Pretty Good House philosophy. Meeting metrics was not the primary goal, but creating a comfortable, highly energy-efficient home that fits into the neighborhood on this tight site was the guiding star. The home features a 12” double stud wall assembly, triple pane tilt-turn windows, and copious amounts of insulation. While the driveway snow melt system (necessary for the belowgrade garage) is markedly not energy-efficient, the home itself performs impressively.
EFFICIENCY: Net Zero Ready
BUILDING ENVELOPE: Slab—4” concrete over 4” of rigid EPS insulation R-20. Foundation Walls—10” poured concrete with 3 1/2” rigid insulation R-22. Walls—Double stud walls with dense packed cellulose R-35. Roof—Flash and batt rafters (spray foam and dense packed cellulose) R-52. Windows—Triple pane American tilt-turn windows. Airtightness—untested
SYSTEMS: Heating and Cooling—High efficiency natural gas condensing boiler. Ventilation—Venmar ERV
SIZE: 3566 sq ft
COST: $240/ sq ft
- DESIGNER: Briburn
- BUILDER: Rainbow Construction
- RENEWABLES: none currently
- ENERGY/PERFORMANCE CONSULTANT: Briburn
Locally sourced Passive House timber frame
THIS FOUR-BEDROOM PASSIVE House is home to a family of three, and includes space for an in-home massage practice and yoga room. The Newsoms chose the property to be near close friends who share their desire to protect the environment and live as much as possible off the land. To this end, many of the materials used in the house were sourced from the area, including locally-harvested pine siding and timbers for the frame, as well as the stair treads and railings. Neighbors cut the timber frames and were involved in erecting the frame as part of a community event.
The house features many non-toxic materials including concrete countertops and stained concrete floors with zero VOC wax, zero VOC paints, bamboo flooring on the second floor and natural linoleum in the upstairs bathroom.
Why we like it: As a passive house, this home enjoys impressive performance and comfort. The home uses a vapor-open truss wall assembly and Danish triple pane windows. It also features a ground loop system that prewarms (or cools) the incoming fresh air for the energy recovery systems (ERV). The home is very tightly sealed with extremely high insulation values and is topped off with an evacuated tube solar thermal system for domestic hot water.
EFFICIENCY: Certified Passive House. $596 annual cost for heat and electricity.
BUILDING ENVELOPE: Slab—8” concrete over 12” of rigid EPS insulation R-72. Walls—9.5” TJI (wood I-joist) studs combined with 2×6 wall construction filled with dense packed cellulose insulation R-50. Roof—Truss system with 36” of loose fill cellulose R-120. Windows—Triple pane Danish tilt-turn. Airtightness—ACH50 – 0.6
SYSTEMS: Heating and Cooling—ductless mini-split heat pump. Ventilation—Zehnder ERV with ground loop system. Hot Water—Evacuated solar thermal tube array and storage.
SIZE: 2016 sq ft
COST: $156/ sq ft (includes solar hot water, but not PV)
- DESIGNER: Maine Passive House
- BUILDER: Maine Passive House
- RENEWABLES: Revision Energy (Solar hot water), Garbo-Kane (solar PV)
- ENERGY/PERFORMANCE CONSULTANT: Maine Passive House
High performance in a quiet modern aesthetic
CUSTOMIZED VERSION of GO Logic’s 1600 sf predesigned high performance home model, this 3-bedroom house features exceptionally low energy costs, amounting to $600 a year in electricity and just $200 additional for biobricks for the wood stove. It features an open interior with exposed concrete flooring throughout, an important element of the home’s energy performance that helps to regulate interior temperatures.
Making use of passive solar gain and a highly-insulated shell, the home was built to the German Passive House Standard, which offers a 90% improvement to space heating when compared to a code compliant home. It has a near zero approach to energy usage, meaning that the energy produced by the 4.6 kwh solar panels nearly covers the total energy needs for the house.
“The house is draft free and comfortable all the time,” said the owner, commenting further that as of Dec. 21, they had yet to turn on the heat and the temperature in the house had not dipped below 65 degrees.
Why we like it: While not technically a Passive House, this home was designed to meet the passive house standards. This home delivers high performance in a quiet modern aesthetic. As expected with a Passive House, the building envelope features high levels of insulation, but its more unique construction method can be found at its foundation: a raft slab of concrete and granular fill that rests on a sub-slab of 8” of expanded polystyrene insulation that turns up 90 degrees at the foundation edge to maintain a continuous exterior layer of insulation around the entire home.
EFFICIENCY: Near Passive House standards. Heating energy demand – 4.5 kBtu/ sq ft per year. $600 annual cost for electricity and $200 for biobricks for the wood stove.
BUILDING ENVELOPE: Slab—4” concrete over 8” of rigid EPS insulation R-40. Walls—2 x 6 with 8” SIP using EPS foam R-50. Roof—Truss system with 24” of loose fill cellulose R-78. Windows—Triple pane German tilt-turn. Airtightness—ACH50 – 0.5
SYSTEMS: Heating and Cooling—Electric baseboard + wood stove. Ventilation—Zehnder ERV.
RENEWABLES: 4.6 KW Photovoltaic array.
SIZE: 1680 sq ft, not including open deck and garage
COST: $250/sq ft including site, garage, deck, solar
- DESIGNER: GO Logic
- BUILDER: GO Logic
- RENEWABLES: ReVision Energy
- ENERGY/PERFORMANCE CONSULTANT: GO Logic
Cozy cabin with nearly unparalleled performance
THIS OCEANFRONT HOME was designed by George Penniman, principal at George Penniman Architects, along with his wife and landscape architect, Anne Penniman. George was inspired to build a Passive House after training as a Certified Passive House Designer with the Passive House Academy in Brooklyn, NY & Ireland.
The house was built on helical piers, affording a very light environmental footprint. There is no slab or basement, eliminating the need for heavy site work. Utilities run underground and up through an insulated pod which begins 4’ below grade and continues up through the heavily insulated floor system.
All finish materials were sourced as locally as possible. The exterior white cedar and hemlock, the pine that was used on the interior walls and the ash floors were all sourced from Maine forests. Additionally, stone in the entry and the tile backsplash is Englishman’s Bay granite quarried in Maine. Other materials chosen for their sustainable and non-toxic qualities include PaperStone countertops, Vermont Natural floor stain and finish, low VOC paints, and plant-based oil for natural wood wall finish.
The house was designed to accommodate a future addition.
Why we like it: This home is excellent proof that pre-fab construction can more than match the performance of onsite custom construction. This home is built using extremely tight vaporopen assembly panels (including the floor) and erected in place on site. The all-wood triple pane windows add to its performance and New England cabin charm. The super insulated structure is then founded using helical piers that lift it off grade. The result is a modern, cozy cabin that has nearly unparalleled energy performance.
EFFICIENCY: Pre-Certified Passive House. Heating demand – 4.1kBtu/sq ft per year. Primary Energy demand- 36.8 kBtu/sq ft. $400 Estimated annual cost for heat and electricity.
BUILDING ENVELOPE: Foundation—Built on helical piers. 24” TJIs with dense pack cellulose under floor R-81. Walls—Panelized 117/8” TJI (wood I-joist) studs combined with 2×4 wall construction filled with dense packed cellulose insulation, covered with mineral wool R-55. Roof—cathedral truss rafters filled with dense packed cellulose R-111. Windows—Triple pane European tilt-turn. Airtightness—ACH50 – 0.4
SYSTEMS: Heating and Cooling—ductless mini-split heat pump. Ventilation—Zehnder ERV.
SIZE: 1,300 sq ft
- DESIGNER: George Penniman Architects / Anne Penniman Associates
- BUILDER: Ecocor High Performance Buildings
- RENEWABLES: solar planned for future
- ENERGY/PERFORMANCE CONSULTANT: Ecocor High Performance Buildings