Nice Shades: 24 Storey Passive House Tower Built in Manhattan

ZH architects faced a lot of serious challenges here, and came up with innovative solutions.

Passive House design does not mean it's just for houses; more taller buildings are being done to the tough standard now. One of the most interesting, and one that busts a whole lot of misconceptions, is 211W29, a 24 storey mixed use building in midtown Manhattan. ZH Architects explain why:

Not only committed to developing a building that reflects the diversity of NYC, 211W29 also endeavors to provide a new standard of comfort in rental apartments by meeting the Passive House criteria. Passive House construction delivers a higher quality of construction which includes continuous filtered air, triple glazed windows to reduced street noise, and an overall lower consumption of energy for the entire building.

© Stas explaining building/ Monte Paulsen

But it's not easy to do, especially when sandwiched between two other buildings on a lot only 45 feet wide. During the North American Passive House conference in New York City I toured the building with ZH principal Stas Zakrzewski.

One of the biggest problems in building between buildings is how you build a wall right up against the neighbour. Standard practice is to lay up concrete blocks, which you can do totally from the inside.

© AAC block/ Monte Paulsen

But concrete block walls do not have a very high insulating value, so to build a Passive House quality wall with all the required insulation would get very thick, a problem on such a narrow lot. Stas took a really interesting approach by using Autoclaved aerated concrete (AAC) blocks. A Swedish invention, they are made of a type of foamed concrete with quartz sand, gypsum, cement and a bit of aluminum powder, which reacts with calcium hydroxide to make hydrogen bubbles. It's then cut into blocks and hardened in a steamy autoclave. The blocks are 80 percent air (the hydrogen escapes and is replaced by air) and weigh far less than conventional blocks.

But its most important feature in the Passive House world is its R-10 rating for an 6-inch block. That is a big chunk of the way toward a passive house rated wall (the exterior walls here average R-33). It's also fireproof and it provides a great surface for the yellow liquid-applied Sto Gold air barrier. AAC blocks have been around for years and are common in Europe; read more about them on Green Building Advisor.

Nice Shades

Flatiron Building in 1909/Public Domain

Another important issue in Passive House design is solar control; because of the energy consumption from air conditioning, you want to deal with the solar gain before it gets in instead of paying to remove it after. That's why so many New York buildings used to have awnings put up every summer, like in this 1909 photo of the Flatiron Building.

Lloyd Alter/ note the shadows on the windows and building/CC BY 2.0

You also don't want the windows to be too big; these Schucco triple-glazed windows are very expensive, and and even the best window is not as good as a regular wall. That can make it hard to make a building architecturally interesting. (See in praise of the dumb box.) Stas and his team came up with a great solution to both solar control and architectural design: little permanent metal awnings and shading devices around all the windows. You can see in the photo how well they work on a sunny afternoon.

Pipes and conduits on blocks of insulation / Lloyd Alter/CC BY 2.0

There are so many little things that you have to think about with Passive House design, and you have to get all the trades working together. A favourite example from the mechanical spaces: these pipes and conduits get installed early in the construction, long before the wall enclosing the space gets built. So instead of just being bolted onto the structure, they are mounted on big blocks of rigid foam that act as thermal breaks, and will get buried in the final wall. I can imagine that the trades thought somebody was nuts to specify such a thing, but that's how you have to plan ahead for Passive House.

Lloyd Alter/CC BY 2.0

I don't have a lot of photos of the interior, because I did not get into any finished spaces, but I do know that these will be very nice apartments, without a lot of street noise, but with lots of ventilation and managed fresh air. I suspect that in a few years, this will be the standard that everybody wants and might even pay a premium for. It's worth it.