1 Bryant Park in New York, which opened recently to great fanfare as the first LEED Platinum skyscraper, highlights one of the biggest problems with LEED: Because it's a system of additive credits, you can accumulate credits in a number of ways while doing some really silly and unsustainable things, like building with a glass curtain wall. Let’s look at the glass wall problem first, then look at the LEED problem.
the Glass Problem
Here’s an image of 1 Bryant Park. The rest of the images are of other buildings in other cities, but it doesn’t really matter because it’s a problem everywhere that there’s a summer or a winter.
Why is this a problem? There are several reasons:
1. The smartest glazing I’m aware of is from a company called Serious Materials. They really live up to their name; everything they sell is very high-performance. Yet their best glass isn’t quite as good an insulator as a plain old 2x4 wood frame wall with fiberglass batt insulation. So the best glass you can buy leaks more energy than the cheapest tract house wall it’s legal to build in most places. And most glass isn’t nearly as good as Serious. Typical “high-performance” glass curtain walls leak three times as much energy.
2. Ask anyone on the street whether they like more light or less light in their workplace, and most of them say they like more light. Yet a solid wall of glass over-lights a room so badly on a sunny day that curtain walls are typically tinted or mirrored to exclude more than half of the light (often up to 2/3,) otherwise it would be so bright you couldn’t work. So clearly, you don’t need the entire wall to be made of windows in order to daylight the space. Windows with clear glass occupying 1/3 of the wall would provide the same amount of light as a wall of glass that lets in 1/3 of the light that shines on it. Old buildings did this naturally, it should be noted.
3. A typical office tower in most regions requires air conditioning year-round because of the amount of heat generated by lights, computers, equipment, people, etc. This means that these buildings never need any solar heat gain... yet half of the walls of a square tower face either east or west, and anyone who knows anything about passive heating and cooling knows that one of the very first things you want to do is to reduce east- or west-facing glass because that’s where the sun is low in the sky, shining directly in the windows.
4. Glass curtain wall buildings carry health consequences for their occupants that have been well documented over the years. There are a number of reasons for this that are beyond the scope of this blog post, but you may have heard of one of the big ones, which is Sick Building Syndrome (SBS.)
I did this rant on glass walls while at the AIA convention recently. More recently, Alex Wilson did an excellent and well-documented post on the problems of glass wall buildings on Building Green. You need a membership to get to the article, but his stuff is so good that it’s well worth the annual subscription. The bottom line is that fewer things you can do to a building are less green than coating it in glass... which brings us to the other item:
the LEED Problem
Before getting into the details, let me say that I’m a big supporter of the mission of the US Green Building Council, which is to provide incentives for building in a more sustainable fashion. As a matter of fact, I serve on a USGBC Technical Advisory Group that advises on issues having to do with building location and context. Our work primarily affects LEED-ND, the neighborhood rating system. So I’m not a typical LEED-basher... but the system isn’t perfect, either.
The glass wall problem shows one fault of an additive points-based system: you don’t have to consider far smarter systems that are fundamentally better, such as walls that are solid, punctuated with only enough windows to provide the light, ventilation, and view that we need. Instead, you can do something much less intelligent like a glass wall and score points for doing so more efficiently. In other words, it’s a system that encourages us to continue our enormously wasteful modern construction systems, so long as we build them a bit more efficiently.
Here’s another illustration of the weakness of an additive point-based system: adding a bike rack and a changing room scores as many points as re-using 75% of an existing building. Is biking to work good? Absolutely. But there’s no question which is easier for a developer to do: “crank up those bulldozers and trash the existing building, boys... we’ve got our LEED credit with the bike rack!”
It’s important to point out that these issues are not problems with LEED calibration. The USGBC hasn’t done a bad job fine-tuning LEED, in other words. Rather, these are structural flaws of additive points-based systems. It’s time to consider a change.
Note: If any of the images above are useful to you, they’re available at high resolution for printing or download on my Zenfolio site. Just click on the image and it’ll take you there. The only exception is the 1 Bryant Park image, which isn’t one of mine.
Friday, July 2, 2010 - 05:23 PM
Nice job of covering many of the arguments against glass curtain walls. Here is a blog post by Alex Wilson that summarizes some of the information in his Environmental Building News article. Why are architects and developers drawn to all-glass facades, despite their considerably worse performance in terms of energy and comfort? Wilson quotes a female architect who says it's a sexual thing: "A woman architect I interviewed for the article even suggested that architects are drawn toward all-glass buildings for the same reason they are attracted to women's lingerie--the façades being 'sleek, smooth, sexy, shimmering, simple--and simultaneously transparent and mirroring.' " Are all-glass building the Victoria's Secret of the architecture world?
Friday, July 2, 2010 - 06:33 PM
Add another point to your list... most of your pics are from Dallas and think about where all of that reflected energy goes when the buildings are skinned with mirrored glass precisely to prevent solar/light gain inside the walls... THE STREET! A paved city like Dallas with very few trees in downtown already has enough of a heat island effect without the bounce light/heat off the high rise offices. I've heard the condos around Gehry's Disney Concert Hall in LA become as much as 15 degrees warmer in the summer from reflected energy from the platinum skin, I wonder what these buildings to do Dallas's public realm.
Wednesday, July 28, 2010 - 10:52 AM
Those are some very compelling arguments. The glass curtain wall is definitely a hold-over from a more careless (or ignorant) phase in architecture. We shall see how long it remains popular. In the meantime, if you want to learn more about this type of construction, I'd check out the Sweets Network from McGraw-Hill, my employer. They have a great directory of glass curtain wall manufacturers that you can contact with questions.
Steve, thanks for the article. I do have some concerns about your first 4 points on all glass facades, especially if you are basing this on One Bryant Park.
1. Improving the skin performance on the exterior wall of a 2.2 million square foot skyscraper barely puts a dent in the overall energy consumption of the building. At One Bryant Park, only 6% of the buiding's total energy usage is directly related to the exterior wall (heating and cooling of the perimeter). This is, however, vastly different if you are talking about single-family residential where roughly 40%-50% of the energy usage is directly related to the exterior wall. So, even if you improved the performance of the exterior wall of One Bryant Park by 66%, which is drastic I think, you've only affected 4% of the buildings total energy profile. So, what they did at One Bryant Park was very smart: they create power for the building on site at three times the efficiency of the grid. Significantly less waste.
2. There is ceramic frit embedded in the curtain wall of OBP that solve the exact problem you are referring to. There are solutions to these issues you bring up.
3. It is true that it requires air conditioning all year long, however, not around the perimeter of the interiors. Those do, in fact, benefit from solar heat gain in the winter.
4. Sick Building Syndrome has nothing to do with glass walls. It is an indoor air quality issue related to construction/design methods. In fact, you also fail to mention the fact that the air inside One Bryant Park is cleaner and healthier for you than anywhere in Manhattan. The building is basically a giant air filter for NYC. The air going out is cleaner than the air going in.
If you'd like to discuss more, email me at 1rbrowne(at)gmail(dot)com.