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Green Building News

Aiming for Passivhaus in Boston

Powahouse, a three-unit, three-story condominium under construction in the city’s Roxbury neighborhood, is on track to meet the standard

Airtight on a corner lot in Boston. This three-story, three-unit condominium in the Roxbury section of Boston is being built to meet the Passivhaus standard. The design-and-construction team, Placetailor, expects the building to be ready for occupancy in August.
Image Credit: Placetailor
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Airtight on a corner lot in Boston. This three-story, three-unit condominium in the Roxbury section of Boston is being built to meet the Passivhaus standard. The design-and-construction team, Placetailor, expects the building to be ready for occupancy in August.
Image Credit: Placetailor
Unit X, one of three condominium units in Powahouse, is a 1,000-sq.-ft. two-bedroom. It listed at $247,000. Powahouse’s Unit Y, a 1,100-sq.-ft. two-bedroom, listed at $279,000. Because temperatures were close to freezing in February, when the slab was poured, arrangements were made to keep the concrete above 50 degrees Fahrenheit for at least 48 hours – long enough for it to properly cure. Walls started going up in early February. Exterior walls of Powahouse are insulated to R-59.

It might have left a few people feeling especially uneasy about climate change, but the Northeast’s strangely dry, mild winter did at least allow construction to continue at a relatively brisk pace on Powahouse, a three-unit condominium going up on a corner lot in Boston’s Roxbury neighborhood.

Excavation began on December 9. By January 23, a frost wall had been poured just outside the slab perimeter and the construction crew, led by local design-build firm Placetailor, had prepped a 2,000-sq.-ft. area inside the frost wall for the pouring of the ground-floor “raft” slab. The security fence surrounding the site had been draped with tarps. Powerful heaters were brought in to help warm the area, and 40 cubic yards of concrete were preheated and mixed with an accelerator to help the mixture set faster once it was poured into place.

The pour was a success, the winter weather continued to more or less cooperate, and the pace of construction now has Placetailor predicting that the three-story building will be ready for occupancy by the end of August. Not long after that, Powahouse is expected to qualify for Passivhaus certification.

Promising performance numbers

Designed in collaboration with Schneider Studio Design, the project originally included four units, notes Placetailor principal Simon Hare, but two of the units were sold early on to a single buyer and were then redesigned for the buyer into a townhouse-style home that, at about 2,000 sq. ft., comprises roughly half of the building’s interior floor space. The other two units, featuring floor plans that interlock with each other, were marketed by a Realtor and recently sold. One, Unit Y, is a 1,100-sq.-ft. two-bedroom that was priced at $279,000; the other, Unit X, is a 1,000-sq.-ft. two-bedroom that was priced at $247,000.

Hare adds that, so far, the building appears to be on track to meet performance expectations. An initial blower-door test, conducted on May 4, showed 0.28 air changes per hour at 50 Pascal pressure difference. The project’s Passive House Planning Package modeling puts the under-slab insulation value at R-37 and R-21 around the slab edge. Exterior walls are R-59, the party wall is R-40, and the roof is a minimum of R-77.

Placetailor went with Schuco SI82 triple-glazed, tilt-turn windows, Schuco doors for two of the main entries, and another Schuco door for access to a third-floor patio. Makrowin doors are used for one main entry and another patio-level entry. Each unit is equipped with a heat recovery ventilator – a Zehnder ComfoAir 350 for the large condo, a ComfoAir 200 for Unit X and one for Unit Y. Auxiliary heat will come from Mitsubishi Mr. Slim 9000-btu mini-split heat pumps – one for each unit.

A project that blogs for itself

Hare explained that a previous Placetailor project – the reconstruction of Pratt House, a former gunsmith shop built in Roxbury in the 19th century – caught the attention of an angel investor, who agreed to help back the builder should an opportunity emerge in Roxbury for a Passivhaus condo project. Three years later, that project materialized as Powahouse (a play on Powerhouse, with a Boston accent), with Placetailor serving as developer and builder.

The project got another nudge forward with the early sale of the first two units, now combined into a four-bedroom and known as Unit Z, for $490,000. That price, Hare notes in an email to GBA, reflects a discount because the offer included a “very generous cash down payment.” At this point, Hare says, projected construction costs are $135 per sq. ft., excluding the cost of the lot and “soft costs” such as fees for consultants, design, zoning, management, and insurance.

A Powahouse blog, including plenty of photos, has, with Placetailor’s help, created a “voice” for the building — a first-person (first-building?) narrative that highlights construction details and celebrates small victories. Click here for a look at the building’s development so far.

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