Urban Multifamily Passive House in the Northeast Corridor

Condos and Rental Buildings in Washington, DC, Philadelphia, New York City, and Boston

As you may know, the Passive House standard applies to all building types, not just single-family houses. In fact, the first Passive House was a block of four townhouses built in 1991. The Northeast Corridor is a great location for multifamily buildings that meet the Passive House standard due to the high cost of energy, relatively mild climate, and good solar access. The Northeast Corridor also generally has great transit access, which reduces transportation costs and increases home values.

Passive House Design Basics

Form and orientation: Multifamily buildings in this region don’t have to be simple boxes facing south. Site and zoning constraints will likely determine the shape and size of the building more than energy performance concerns. That’s OK because larger buildings have relatively less surface volume, so they lose less heat. As an example, one multifamily Passive House retrofit project Duncan Architect consulted on in Brooklyn had the majority of its solar gain from north-facing windows, but we were still able to reduce the annual heat demand by 90 percent.

Structural System: Wood has less embodied energy and a smaller carbon footprint than steel or concrete. However, fire codes prevent the use of wood structures in many urban areas. Fortunately, the Passive House standard allows any structural material as long as thermal bridges (interruptions in the insulation) are avoided.

Windows: High performance triple-glazed windows are comfortably warm to the touch even on the coldest winter days. South facing windows can actually provide a net heat gain in the winter. Properly designed exterior shading will keep the apartments from overheating in the summer. Passive solar gains can offset some of the heating costs of the building, but because of their expense, windows should not be oversized. Residents can open their windows as they wish, but they don’t have to in order to get fresh air because a special ventilation and air filtration system is part of the Passive House package. Triple-glazed, airtight windows also reduce street noise, which is an important selling point in urban areas. The Passive House Institute certifies windows for “cool, temperate” and colder climates. On this map “cool, temperate” is shown in cyan and includes most of the US. weltkarte_und_klimazonenhttp://www.passiv.de/_images/03/00_zertifizierungskriterien/01_transparente_bauteile/weltkarte_und_klimazonen.jpg

Insulation: Passive House designers optimize the thickness of insulation using an energy modeling tool called PHPP. In brownstones, rowhouses, and midrise apartment buildings, this typically results in walls that are as thick as the traditional buildings in the area. In New York City developers can take advantage of floor area deductions for high-performance walls more than 8” [200 mm] thick. A zoning analysis by Duncan Architect for a proposed hotel tower in Brooklyn showed its developers that they could add an entire floor by improving the performance of the walls.

Thermal mass can help regulate temperature. However, it is more useful in regions other than the Northeast, where there are cool summer nights.

Airtightness is a key requirement of the Passive House standard. An airtight building enclosure with proper ventilation and walls that can dry out if they get wet prevents “sick building syndrome”. An airtight building is also more comfortable because there are no drafts. Last but not least, it costs less to operate because there is virtually no heat loss (or heat gain in the summer) due to uncontrolled air infiltration.


Special ventilation units provide constant fresh filtered outdoor air to the apartments while exhausting kitchens and bathrooms without significant heat loss. They are called heat recovery ventilators (HRVs). Some also recover humidity and are called energy (or enthalpy) recovery ventilators (ERVs). Humidity recovery allows mechanical ventilation without drying the air too much in the winter or bringing in too much humidity in the summer.

Heating: Within a Passive House building enclosure any type of heating system is possible. Radiators under the windows are not required for comfort in a Passive House, so the heat source can be located anywhere. Mini-split air source heat pumps provide heat two to three times as efficiently as direct electric radiators. Electric warming mats under tile in the bathroom are nice luxury features that don’t cost a lot to install. Gas boilers can provide heat and domestic hot water. Natural gas is currently a fairly inexpensive fuel, but that may change in the future with carbon taxes on fossil fuels. Ground source heat pumps are typically overkill for a single-family Passive House because the heat loads are so small. However, a large multifamily may be able to take advantage of the economies of scale. Rental buildings should include heat in the rent to avoid the costs of individual metering and to match market expectations. Condo buyers, on the other hand, are more accustomed to paying for their heat and owning their heating equipment. In this case it makes sense to provide decentralized heating units and to market the extremely low heating bills.

Air conditioning is needed in DC, Philadelphia, and NYC. In Boston many apartment dwellers survive without A/C, but the summer humidity does exceed recommended levels. Central air is expected for condos while being an opportunity for market distinction for rental buildings.


Affordable housing should take into account heating and cooling costs as well as transportation costs. Urban multifamily Passive House addresses both. For luxury apartments, the Passive House standard assures unparalleled comfort and healthy indoor air. (And, yes, affordable apartments get those benefits, too.)

Contact us to design your next urban multifamily Passive House. Email greg@duncanarchitectpllc.com for more information.


Deutsche Bank Towers Renovated to Use 89% Less CO2

The German magazine Detail provides a very detailed—naturally—summary of this LEED Platinum retrofit.

The 155-meter tall towers were completed in 1985 and renovated this year to the USGBC’s highest rating, while also achieving certification by the German DGNB.

Recycling: 98% of the construction debris was recycled.

Heating and Cooling: 67% reduction in energy for heating and cooling.

Electicity: 55% less electricity required.

Water: 74% less water.

Carbon Dioxide: 89% less CO2 per year (equivalent to removing 6000 cars from the road).

Bridge School wins Aga Khan Award for Architecture

Bridge School (c) Aga Khan Award for Architecture / Li Xiaodong

Hanging Bridge (c) Aga Khan Award for Architecture / Li Xiaodong

The “Bridge School” bridges the two parts of the small village of Xiashi that lie on either side of a small creek that runs through the village. The structure is created by two steel trusses that span the creek with the space between them housing the functions of the school. Suspended from the structure and running below it is a pedestrian bridge for the people of the village to use.  more…

Location: Xiashi, Fujian Province, China (Asia)
Architect: Li Xiaodong (Atelier)
Client: Xiashi Village
Completed: 2008
Design: 2008
Site size: 240 m²

This combination school, public library, and pedestrian bridge is simple, beautiful, and beneficial to the community.  It is one of five winners of the Aga Khan Award for Architecture.  See the video on the Aga Khan website.

Photos from Nathan Harger Opening

Nathan Harger's Opening Reception

I found out about this photography exhibit on the ArtCat website.  Nathan Harger does amazing black and white photos of architecture and urban infrastructure.  His photo below of the Wonder Wheel at Coney Island recalls Futurist paintings and Constructivist designs while allowing the object of the amusement ride to be recognizable.  The opening reception is at the Hasted Kraeutler gallery in West Chelsea on Thursday, December 9, at 6:00 pm.

Nathan Harger's Wonder Wheel, Brooklyn, NY 2009

Nathan Harger's Wonder Wheel, Brooklyn, NY 2009

Books I'm Reading

Recreating the American Home: The Passive House Approach, by Mary James

The diversity of the ten projects in this book is pretty amazing — from the restoration of an historic 19th century brownstone in Brooklyn, NY, to a large single-family home in the high desert of Salt Lake City, Utah.  The book also includes affordable housing and a house in the hot and humid climate of Louisiana.  Aesthetically, the houses are very diverse as well, although they are all fairly conservative.

Grid Rocks!, by George Duncan

chaotic exuberance, stochastic turbulence, architectural surrealism

This book is based on the art displayed in his solo exhibition at the Artistas de Santa Fe Gallery in New Mexico.

Mastering Autodesk Revit 2011, by Eddy Krygiel, Phil Read, and James Vandezande

I love this book because it’s easy to follow and contains real-world examples of how to use building information modeling (BIM) processes, not just software.

Green Building Myths

10 Green Building Myths by Green Building Advisor

1. New York City is an environmental nightmare
2. Walls have to breathe
3. Renovation is less expensive than new construction
4. Spray polyurethane foam creates an air barrier
5. Caulking the exterior of a house reduces air leakage
6. R-value tests only measure conductive heat flow
7. Air conditioned homes don’t need a dehumidifier
8. Efficiency Rating Labels On Appliances Account For All Types of Energy
9. In-floor radiant heating systems save energy
10. Green building helps save the environment

USA wins again


At 214 square meters new American homes are almost three times as large as British ones.  Average household sizes are about the same in America, Australia, and the UK, so that doesn’t explain the difference.

A post by Jayne Merkel in the New York Times talks about “When Less Was More” in American homes.


Guatemala Volcano

An active volcano seen from Alotenango, Guatemala in 2006.  The Orange Crush stand is literally a decorated shed, utilitarian and expressive like much of Guatemala.

Ametrica! Metric America

In 2006 Amy Wang won an Adobe Design Achievement Award for her student work in graphic design advocating metrication in the US.


In her last year at SVA, Wang drew together her diverse experiences — cultural, social, and academic — to come up with what later seemed an inevitable thesis. Ametrica! is a cheeky but helpful campaign to convince the United States to join the rest of the world in converting to the metric system. It won an Adobe Design Achievement Award (ADAA) in the Environmental Design and Packaging category, as well as a grant from the Sappi Ideas That Matter program to print the project as a book. Soon she will mail the 1,000 copies to members of Congress and key industry leaders. Ametrica! also earned her a place in STEP Inside Design’s 2007 Field Guide to Emerging Design Talent.

Ametrica! project by Amy Wang

Ametrica! project by Amy Wang