Prioritizing Building Envelope ResilienceThis post was written as a collaboration between 475 and ZeroEnergy Design ZeroEnergy Design (ZED) is one of the northeast's leaders in high performance residential design. A self-described "modern green architecture and mechanical design firm", ZED is a rare firm that puts modern and green together into a cohesive whole. At ZED, green means "exceptional energy performance". Case in point: they list energy use intensity in kBtu/sf/yr on their project portfolio pages. ZED customers don't have to choose between "high design" and "high performance".
If you take the time to delve into ZED project web pages, you'll always find plenty of information about energy performance and other details related to sustainability. When it comes to building envelopes, super-insulation, airtightness, triple-pane windows and other high performance items are "non-negotiable". That's because resilience is ZED's ultimate goal. And 475's Pro Clima airtightness and weather protection systems play an outsize role in ZED's resilient enclosure details.
Resilience via the building envelopeResilience can be defined as the "capacity to recover quickly from difficulties". Or simply: toughness. The natural order of the universe is entropy, which means a decline into disorder. It's a given that both the outside environment and interior conditions change continually, often in ways that place the building and occupants under stress. Resilience is the force that rights the ship and keeps the building operating optimally, especially when the seas are rough. When the enclosure is resilient, the long-term durability and thermal performance of the building enclosure is assured. And by keeping the building structure warm, dry and protected, resilience has a multiplying effect that enables the following additional benefits:
Case Study: Lincoln Net Positive FarmhouseTo achieve resilience, ZED has developed proven envelope strategies centered on airtightness and super-insulation. A perfect illustration of ZED's strategies is their recent single-family residence in Lincoln, Massachusetts. Built by Thoughtforms Corporation, the home won Fine Homebuilding's 2017 Best Energy-Smart Home Award. While evoking the "nostalgia of a traditional Massachusetts farmhouse", it meets ZED's 21st-century demands for energy performance and resilience. ZED went with their "go-to assembly" that has been a proven performer on many of their residential projects. The basic ingredients are exceptional airtightness, insulation and moisture protection. Other passive factors such as orientation, form, layout and window locations also play important roles, as well as efficient active systems.
1. High performance moisture protectionThe first step for a resilient enclosure is keeping the weather out with a robust weather resistant barrier (WRB). ZED starts with Solitex Mento 1000 as their multi-tasking air barrier, and also the most advanced WRB on the market. It's a 3-layer monolithic membrane that’s so waterproof it resists a 33-foot water column - far beyond conventional micro-porous housewrap performance. At the same time, it's reliably vapor open to allow moisture to dry outward well into the future. Mento 1000 is applied shingle-style for uninterrupted drainage from the roof ridge all the way to the foundation. Seams are taped with Tescon Vana airtight tape - tape that is also waterproof and vapor open to help optimize the enclosure drying potential.
2. Exceptional air sealingThe Lincoln Farmhouse tested at 0.27 ACH50 - one of the better blower door test results in the US! At ZED, airtightness routinely comes in significantly better than the 0.6 ACH50 required for Passive House. Planning together early as a team with Thoughtforms helped to ensure success. Airtightness has multiple benefits. First, it allows the installed insulation to perform to its full potential. Without airtightness, insulation performance can be degraded by as much as 80%. But improved insulation performance is just the beginning. Airtightness also provides greater comfort, resilience and cost savings – essentially for free. Once a robust airtightness strategy is in place -and contractors work together to implement it - getting from 0.6 to 0.3 ACH50 gets easier. And each airtightness improvement means less moisture in the walls and roof, which translates to a drier and more resilient enclosure. Another important feature of the airtight layer on ZED projects is that it's well protected and kept warm by exterior insulation. But in the end, the longevity of the materials themselves is the primary concern. 475 talks about “permanent airtightness”, which means one thing: airtight materials should be airtight for longer than the building is expected to last. And we don’t mean 30-40 years as for conventional homes - we mean high performance buildings that will last 100+ years. This permanent adhesion of Tescon Vana tape has been independently verified by the University of Kassel using accelerated aging tests.
3. Continuous exterior super-insulation and high performance windowsWhen it comes to insulation, ZED routinely goes way beyond code, and the Lincoln Farmhouse is no exception. The roof is R-69 and the walls are R-44. The entire enclosure is thermal bridge free, with continuous lapped rigid polyiso foam insulation boards at the exterior. This means no kinked isotherms where cold spots could lead to condensation. Spray foam is avoided entirely. Instead, dense-pack cellulose fills the wall and roof bays with ecological, low-embodied energy insulation that helps the enclosure to dry inward. High performance triple-pane windows complete the super-insulated enclosure. Location of openings are optimized for daylighting and passive solar gain, while losses are minimized with airtight integration to the Mento 1000 airtight wrap. Exterior Tescon Vana and Profil window flashing tapes are waterproof yet vapor-open to ensure the windows stay as dry as possible and avoid mold. Self-sealing Extoseal Encors sill tape is a guarantee that any moisture around the windows can't get into the building. Avoiding moisture at windows is one of the keystones of resiliency. The super-insulated airtight envelope means that during a storm with a power outage, heat loss will be very slow – taking multiple days to drop to 60 degrees even with no heat source. This form of resiliency - also called Passive Survivability - means far better comfort, even in the most extreme or catastrophic conditions.
4. High performance all-electric systemsHigh efficiency all-electric systems complement the high performance building envelope. The HVAC system, comprised of a Mitsubishi air source heat pump (ASHP) and a Zehnder energy recovery ventilator (ERV), ensures that the house stays warm in the winter, cool in the summer, and provides a constant supply of fresh, clean air throughout the year. Ducted distribution systems serve the first and second floor while floor-mounted ductless consoles serve the conditioned basement and attic. Domestic hot water is provided by a heat pump water heater from Stiebel Eltron that operates about 3 times more efficiently than a conventional electric hot water heater. High efficiency appliance examples include induction cooking in the kitchen and a condensing dryer for laundry. A circuit-by-circuit energy monitoring system allows the owners to track their energy consumption, production, and troubleshoot anomalies. The all-electric home consumes 70% less energy than a code-built house, and with a 13.8kW array of solar panels produces 67% more energy annually than it consumes, making it a “net positive” home.
PerformanceOn a monthly basis, the home operates at an energy surplus 10 months out of the year. Energy consumption exceeds production only during the coldest and darkest months (December and January). For the trailing 12 months ending April 2017, the home’s actual energy consumption was 10,146 kWh total (7.9 kbtu/ft2 EUI) while the actual energy production was 17,151 kWh total. This yielded an annual energy surplus of 7,005 kWh, enough to power an electric car for 20,000-30,000 miles per year.