A Passivhaus Retrofit in Minnesota
A remodeling project in Minneapolis is on track to become one of the first in the U.S. to meet Passivhaus Institut’s EnerPHit standard
Paul Brazelton’s introduction to Passivhaus principles was well timed. He and his wife, Desiree, were contemplating a possible expansion of their 1,400-sq.-ft. three-bedroom home in south Minneapolis when Paul paid a visit to Hudson, Wisconsin, where construction was underway on a 1,945-sq.-ft. three-bedroom that came to be known as Passive House in the Woods.
The notion of building an energy efficient house to a high standard – and relying relatively little on the grid – inspired the Brazeltons to consult with the architect on the Hudson project, Tim Eian, of TE Studio in Minneapolis, about the possibility of applying Passivhaus principles to their remodel. Eian used Passive House Planning Package software to create and update a performance model of the house as the couple suggested a progression of improvements for it, including substantial increases in shell insulation and airtightness.
In the end, the Brazeltons calculated that they could afford to renovate the house to meet Passivhaus Institut’s EnerPHit standard, a version of the Passivhaus standard intended for older homes whose construction features and siting might not accommodate all of the Passivhaus requirements that apply to new construction.
At the EnerPHit forefront
The annual heating limit set by EnerPHit, for example, is 25 kWh per square meter (vs. 15 kWh per square meter for Passivhaus) and the maximum air infiltration rate is 1 air change per hour at 50 Pascals (vs. 0.6 achACH stands for Air Changes per Hour. This is a metric of house air tightness. ACH is often expressed as ACH50, which is the air changes per hour when the house is depressurized to -50 pascals during a blower door test. The term ACHn or NACH refers to "natural" air changes per hour, meaning the rate of air leakage without blower door pressurization or depressurization. While many in the building science community detest this term and its use (because there is no such thing as "normal" or "natural" air leakage; that changes all the time with weather and other conditions), ACHn or NACH is used by many in the residential HVAC industry for their system sizing calculations. @ 50pa for Passivhaus). Based on blogs the the Brazeltons have posted to a website that Paul, a software engineer, created to document progress on the project, it appears as if they’re on target to meet their EnerPHit performance goal and their expansion goal, which will bring the house to about 2,000 sq. ft. and more comfortably accommodate the couple, their three small children, and their dogs.
Right now, the project – which will have R-44 exterior walls and an R-80 roof – is still a work in progress, so the family is essentially part of the design-and-construction team, which includes Eian and Ryan Stegora, a builder based in Apple Valley, Minnesota, who was not initially familiar with Passivhaus builds and retrofits, but, as noted in a recent Minneapolis Star-Tribune story about the renovation, has had little trouble finding his way.
Eian, who trained as an architect in Germany, told the paper that EnerPHit retrofits can cost has much as $50 to $100 per square foot, given the materials and construction details involved, which in this case included insulating the slab and floors with expanded polystyrene, insulating the exterior walls with cellulose, and polyurethane spray foam in the basement.
Once the retrofit is complete, it is expected to become among the first certified EnerPHit remodels in the U.S., joining a list that includes many others in other countries and, if all goes as planned, a retrofit in Harlem, in New York City.
- Paul Brazelton
Dec 6, 2011 11:47 PM ET