Building True Value
The Passive House Building Standard requires an integrated design process. By Michelle Apigian
With its laser focus on exceptional energy reduction, the Passive House Building Standard is the world’s most energy efficient. Applicable to all building types and uses, it not only dramatically reduces utility bills, operating costs and our carbon footprint, but its natural byproduct is buildings that are far more durable, phenomenally comfortable and healthy to be in, and highly resilient. Just as important, this superior quality and performance does not require a comparable increase in cost. What it does require is an integrated design process committed to a holistic approach toward building envelope and systems. It also encourages a partnership between designer and builder and a return to the craft of building, where attention to detail and pride of quality are truly valued.
ICON Architecture is just completing the largest Passive House project in Massachusetts, and one of the first of its scale New England. The Distillery was conceived as a demonstration project intended to set a replicable standard for high-quality, low-carbon development. This infill development in South Boston, Mass., will ultimately provide 65 new artist live-work units that enhance an existing, vibrant artist and business community in an adjacent historic distillery mill. The first phase, expected to be completed at the end of 2016, includes 28 units with parking, new commercial space, a roof deck and a large shared courtyard.
What Does the Standard Require?
Passive House is based on specific, measurable criteria that establish an explicitly low energy budget by setting a maximum limit on space heating and cooling demand, air tightness and primary energy. Heating and cooling loads are effectively the miles per gallon of our buildings, as heating and cooling typically comprise roughly one half of a building’s total energy use. Air tightness is critical to energy but is also fundamental to building durability and moisture control. Primary energy represents our true carbon footprint, taking into account not only all energy used on site, but also how we source our energy and what is lost in translation.
Together, these three criteria ensure that we are building true value – high-quality buildings that are intended to endure and to perform optimally both for the occupants and the owners. While the specific numbers associated with each of the criteria may be difficult to digest, their exceptional nature becomes clearly apparent in comparison. Relative to these criteria, a Passive House building typically performs four to five times better than its code compliant counterparts, and still two to three times better than comparable LEED Platinum projects.
How Does a Project Like the Distillery Get There?
Through radical simplicity and rigorous attention to detail, a Passive House project combines a super insulated, airtight envelope with an intelligent ventilation system and passive solar strategies. Collectively, these integrated measures substantially minimize heating and cooling loads by 80 to 90 percent, reducing overall energy demand by up to 50 to 60 percent and realizing extreme thermal stability.
The Distillery is designed to carefully incorporate these principles through traditional building methods and readily available products. The building is podium construction – a wood-framed (Type 5) building over a concrete and steel (Type 1) deck. Four stories of panelized wood construction, with wood stud walls and prefabricated open web trusses, sit above two levels of garage and commercial space. This standard construction methodology is employed with careful emphasis on the components critical to realizing a Passive House project:
1. Thermal Protection – The building envelope’s walls, roof and floor are designed with enhanced insulation both within cavities and continuously at the exterior to minimize thermal bridging. The 2×8 wood stud walls filled with cellulose insulation are augmented with three inches of rock wool on the exterior for an R-value of 37. At the roof, two inches of minimum continuous EPS sits on top, and the open web roof truss cavity is filled with cellulose for an R-value of over 70. At the separation between the parking and commercial space and the residences above, six inches of continuous EPS provide an R-value of 30.
2. Air Tightness – A continuous airtight barrier carefully wraps the entire Passive House envelope. Zip sheathing at the walls and roof is tied to both liquid applied air barriers at elevator shafts and a continuous poly vapor barrier at the floor. Joints are lapped and taped. With air tightness, the products are simple, but the attention to detail and the sequencing become critical to ensure continuity and therefore performance.
3. Windows/Doors – As the largest penetrations in a thermal/air-tight envelope, appropriately sized and quality windows are fundamental. Thermally broken, triple-glazed windows and doors within the PH envelope ensure an optimal envelope. The percentage and location of glazing are carefully considered, and shading is provided to ensure appropriate amounts of solar gain when needed.
4. Continuous Ventilation – With infiltration all but eliminated, the incorporation of Heat Recovery or Energy Recovery Ventilator (ERV) is essential. Not only does it continuously supply filtered air and exhaust stale air, but by passing incoming and outgoing air through this heat exchanger, it also minimizes the temperature delta of the incoming air. In the Distillery, each unit has a small ERVs in a closet at the exterior wall, which minimizes the insulated intake and exhaust ducts.
5. Heating/Cooling – Minimal active heating or cooling systems are then required, and provided in the form of individual air source heat pumps at each unit.
Radical But Realistic
While the enhanced thermal envelope and detailing can be a premium, this is offset by much reduced heating and cooling equipment and associated ductwork. When we take into account a substantial life-time reduction in operating cost, any initial cost premium should see a payback of only a few years. Should renewable energy be an option, Net-Zero or Net-Positive becomes easily feasible.
In the context of properties that will be owned and managed for years to come, this makes particularly eminent sense. Coupling the lifetime of savings in energy use and associated operation costs with the substantially higher level of comfort and indoor air quality, the Passive House standard would seem to be ideally suited for multifamily housing and any other long term assets.
Michelle Apigian AIA, AICP, LEED AP, CPHC Associate is an architect, planner and urban designer who combines optimism and pragmatism to design sustainable environments that strengthen communities and celebrate the uniqueness of place. She has worked on a broad array of project types and scales, from large, multi-phase master plans and design and construction of new multifamily developments to strategic infill, adaptive reuse and modernization projects. Her work has achieved LEED certification at numerous levels as well as one of the first Passive House certified multifamily projects in New England. She is a frequent speaker on topics including Building Reuse and Passive House design. She received a B.A. from Dartmouth and an M.Arch and Master of City Planning from MIT.