By Jonas Risen
Energy efficient, sustainable, housing means different things to different people. To some, it provides a way to live self sufficiently—off the grid. To others, it suggests a way to strike a balance with the natural environment. And yet to others, it offers the chance to watch the utility meter run in reverse and get paid by the utility company! But for the most part, the products and systems associated with sustainable housing come with price tags that sour the notion of building green. Now a green building standard called Passive House makes it possible to meet these expectations and more at a cost affordable to almost anyone in the market to build a custom home.
According to Katrin Klingenberg, executive director of the non-profit Passive House Institute US (PHIUS), Passive House is the most energy efficient building standard in the world today, and they “can be heated with the energy it takes to operate a hair drier.” Translation: a savings up to 90 percent on heating and cooling costs when compared with a traditional house. This feat is achieved by designing an almost air-tight, highly-insulated house that combines the use of free energy from the sun with a small, efficient mechanical system that regulates indoor air temperature. Beyond just vaguely suggesting that builders attack energy-efficiency with caulk and insulation, the Passive House building standard is guided by a clearly defined method for designing and building energy efficiency. It even leaves popular green strategies like recycled materials and green roofs up to the individual homeowner to prioritize and instead focuses strictly on energy consumption.
Other than the guidelines for maximizing energy efficiency, the Passive House standard leaves all other decision-making up to the individual. It does not suggest style, have a set of materials, imply a building shape, or dictate how homeowners should live. The building standard is flexible enough to accommodate a number of different looks and can incorporate common elements such as porches, large windows and pitched roofs. One unique consideration is the orientation and shading of the home. Passive House uses the sun as a primary heating source, so siting the building to maximize solar gain in the winter and shade in the summer is important and can make some locations more feasible than others.
Not optional in Passive House however is the quality of the indoor environment. A properly designed Passive House will have exceptional indoor air quality and maintain steady, comfortable indoor temperatures even during the dead of winter. Said another way, no cold spots, no drafts, and no dangerous buildup of toxic elements in the indoor air.
Passive House is effective because it is an integrated system. The Passive House consultant, an essential team member specially trained in the Passive House method, takes into account a set of factors including the project location, the weather, the sun, building size, windows, and the composition of walls, slab, and roof. They also review the interior space layout, mechanical system, and number of occupants for their impact on the energy performance of the house as a whole.
Organizing all of this information would be daunting were it not for a unique piece of software called the Passive House Planning Package. This software simulates a house’s indoor air quality, thermal comfort and energy efficiency before anything is built. It also allows the design team to test various design options in an effort to balance energy efficiency with budget and feasibility constraints.
According to the US Department of Energy, while “uncontrolled and scattered air leakage’’ provides ventilation to control indoor air quality, it consumes roughly one-third of the energy used to heat and cool the home. Blower door tests, which test air leakage, and thermal cameras, which can spot heat escaping through the exterior walls, are tools that ensure a Passive House performs as designed. A Passive House consultant uses these tools, at set times during construction, to identify problem areas and make adjustments while changes are easiest to make. Construction is generally more rigorous than for typical home because of the stringent requirements, and this means that the entire project team must be chosen based on experience and willingness to work in accordance with Passive House. A Passive House certification is granted only once the home meets requirements of both the simulation software and the blower door tests.
Past efforts to build “super-insulated” homes were unsuccessful because of overheating, stale air, and poor moisture control. To make up for the “fresh air” lost by tightening the building envelop, Passive Houses use a ventilation system which continuously brings in 100 percent clean, filtered, outside air to replace air being exhausted to the exterior. The result is interior air quality higher than in many traditional houses, which only bring in fresh air through leaks—don’t worry, you can still open windows for outside air in a Passive House.
Passive House is designed to be the Volkswagen of housing, making energy efficiency affordable for many home owners. That said, an initial investment in energy efficiency is necessary. Based on experience, the premium for insulation and better building components is between 5 to 7 percent of the construction cost when compared to a similar non-Passive House. A Passive House consultant’s work also carries fees not included in most projects and is in addition to the extra construction cost. The argument Passive House experts make is, however, that the higher initial investment is offset by savings from a smaller mechanical system, a growing set of tax incentive programs for energy efficiency, and lifetime of low utility bills. Alternately, cutting just a few square feet out of the house can go a long way to pay for the energy efficiency provided by Passive House.
Jonas Risén is an Architect and Passive House consultant with Ziger/Snead, LLP Architects in Baltimore, Maryland. (zigersnead.com or 410-576-9131)