Trailside Net Zero
Trailside Net Positive Home
At the apex of a quiet cul de sac, footsteps away from the Brunswick Commons trail, was a picturesque plot of land. This was the spot our clients, an active retired couple, chose to build their forever home. As environmentally conscious people, it was crucial to them that their home be as efficient as possible, with at least 100% of its energy coming from a rooftop solar array. A wall of pine trees line the property, making this no easy feat. We were eager to take on the challenge though, and with a thoughtful design by Michael Maines, we created a net positive energy home. Forty-eight solar panels line the roof, bringing in more than enough energy to power the home and give the couple credits to use towards powering their camp in northern Maine. While building this home, we made air sealing a priority, which paid off, giving it a blower door shell test of .125 SCH50 (a passive house requires below .60 ACH50). With twelve inch thick, double stud walls packed tight with recycled cellulose insulation, and heat pumps to cool and heat the interior, this house stays comfortable all year round.
- Design: Michael Maines Residential Design
- Kitchen Design: Balance Design Studio
- Solar and Heat Pumps: Revision Energy
- Tile and Counter Tops: Morningstar Stone and Tile
- Painting: Osprey Painting
- Windows: Logic by Pinnacle Window Solutions
- Images: Carol Liscovitz Photography
The Story
Our clients originally wanted their home to be a certified Passive House, but we quickly discovered that certain characteristics of the property would make it difficult to meet the exact criteria. A mature stand of eastern white pines bordered the site on town land, blocking direct sunlight for much of the day and limiting the amount of solar exposure. This would prove to be our biggest challenge when designing the home, but the trees were community property and there for everybody to enjoy, so they were there to stay. We decided our best course of action would be to build a more conventional design that would still meet, and in the end exceed, our efficiency goals, and would fit in with the existing homes in the neighborhood. We looked to the Passive House principles when designing and building the home and drew upon many aspects of the criteria, including: maximizing solar gain, minimizing heat loss through northern glazing, creating an airtight space, and using triple paned European-style tilt-turn windows.
We began framing the house in December of 2017, the start of a particularly cold and snowy winter. The sealants and tapes used to create an extremely airtight space perform best at temperatures around or above freezing. We were working in conditions below 20 degrees nearly everyday, while also fighting snow and ice build up, which often hinders adhesion. Our team stepped up and met these challenges with fierce determination, taking extreme care to ensure the air sealing process was done right despite the difficult conditions. In the end, our hard work paid off and this turned out to be the most airtight home we have ever built.
One of the most important decisions we made along the way was to use CDX plywood for sheathing. This material is more vapor-open than the more common plywoods used, meaning that if the walls suffered from a leak, they would dry out quickly. There was some skepticism in the building community about the ability to make CDX airtight, but this project proved that it was indeed possible. We also used a vapor open weather resistant barrier from Pro Clima called Mento 1000, which when taped with Pro Clima Vana ensures robust protection from the elements while maintaining the integrity of the vapor-open assembly.
In addition to creating energy efficient homes, we strongly believe in using the most sustainable materials. Over the years we have seen plastic and cementitious materials increasingly replace wood, especially in exterior applications. These materials have a great environmental cost and can be harmful to work with. For example, cementitious products often contain fly ash, which creates a dust that is harmful when inhaled. We believe that wood remains the superior building material for the health of both the environment, and our workers. We worked closely with our clients when building this home to select the wood product that would best serve their needs, and ultimately decided on Western Hemlock for the siding and trim.
The moment we knew this was a high performing home was in the heat of the summer when the drywall was being installed. We placed a regular old window AC unit in a doorway to temper the climate and help reduce the humidity. This single unit was able to keep the entire 2,200 square feet cool and comfortable, with no additional support. We can look at all the numbers and tests, but this moment truly showed the results of our efforts to create a net positive home.
Building this home was a dream project both for us and our clients. They were engaged every step of the way, and their investment in, and excitement about every little detail made the process that much more gratifying. They not only appreciated our attention to detail in the fine finishes, but also in the framing and air sealing. One wintery day as we were building wall panels, one of our clients said “Oh! You’re filling EVERY nail hole? Thank you!” We love building houses, but ultimately our true passion is for pursuing perfection and making our clients’ visions come to life.
Trailside NetZero by the Numbers
Footprint: 2205 square feet
Carbon Offset: Estimated 14,600 lbs of CO2 per year via solar power
Air tightness: .125 ACH50 shell
Air Barrier System:
- Ceiling: Pro Clima Intello smart barrier
- Walls: CDX plywood taped with 3M 8067 and nail holes sealed, each layer of connection to foundation gasketed with sealant
- Windows: Bucks taped with Pro Clima Vana, windows taped to bucks with Pro Clima Profil
- Foundation: concrete
- Sub slab: 10 mm polyethylene vapor barrier taped to foundation with Siga Fentrim
Insulation:
- Roof: (R-65) Loose blown cellulose above ceiling
- Walls: (R-42) 12″ dense packed cellulose
- Windows: (R-5.6) Logic tilt-turn triple-glazed
- Foundation: (R–26) 4″ of Thermax foam
- Subslab: (R-16) 4″ EPS foam
Net positive electrical System:
- Grid tied photovoltaic: 14.34 KW PV production per year from 48 solar panels
Heating System:
- Primary: Three Mitsubishi mini split heat pumps with wall cassettes
- Accessory: High efficiency Rais wood stove
Ventilation: Zehnder Comfoair 350 ERV
Eco friendly materials:
- Cellulose insulation from recycled newspaper
- Wood siding and exterior trim
- Low VOC paint
Local Materials:
- Ash flooring from Fat Andy’s Hardwood
- Eastern white cedar from Yoder’s Sawmill for exterior entryway
- Landscaping pavers from Genest Concrete.