Quote:
Originally Posted by maccoinnich
It is very difficult (impossible?) to do a completely clear glass building under today's energy codes. The closest you can get is a mix of clear and spandrel glass, with insulation behind the spandrel glass. This is what they're doing at Cosmopolitan. In some lights it's difficult to see the difference between the clear and spandrel glass; in other lights the difference is pretty noticeable.
From the renders of the NV I incorrectly assumed that they were using spandrel glass at the floor slabs. Looking through the Design Review drawings I see that it is indeed grey painted metal panel.
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This isn't really answering you directly, but rather more informational for others, as I suspect you know most of it:
Yes. Near impossible. That's why when you see Cosmo from the Fremont it looks like a giant tower of tinfoil when it reflects the sky. The glass has to be so reflective. Same as Ladd Tower or Atwater. Backlit at dusk it will look great though.
The sheer cost of curtain wall verses window wall or framed wall w/punched windows is a huge consideration. It starts at over $80.00 a square foot for a Benson Industries equivalent such as Allen or a Chinese sourced system (What you see on 12West, Park Avenue West, Cosmopolitan are likely Benson...at more than $80 bucks). Compare that to $50 for a window wall (Toro or similar, like on NV, part of the Strand, Benson Tower or The Civic), there's a huge delta to cover in the building budget. Cosmo can afford it with $800/sf average sale prices. Most projects now, cannot.
As for the energy code, baseline target is about 30% total building glazing to make it through a prescriptive path analysis. Doesn't sound like much, does it? It isn't. That's why many buildings look like they have such small windows. Most developers target this threshold, as exceeding the prescriptive path limits requires a trade-off approach or even more time and money consuming... a whole building 'modeled' analysis. This takes a surprising amount of the aforementioned 'time and money', and is more subjective (Ironic considering it's still ultimately applied math) ergo, less surety. It can certainly jeopardize a project schedule and a budget. Partuicularly when the analyzer concludes differently than expected.
Of note, I recall a spandrel curtain wall gets you about an R4 value in insulation so it still often requires a stud wall cavity behind with inboard insulation or rigid exterior insulation to assist in meeting code. More $.
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