Coming from a wood background, it is a bit disappointing that most (low- to mid-rise) curtain-walls or storefront glazed walls contain only aluminum mullions as their support around here (US). It appears that many architects simply don’t specify these in wood. This fact came to my attention again last weekend when I visited the recently completed Koch Center at the Deerfield Academy in Deerfiled, MA (by Skidmore, Owings and Merrill). Contrary to common building practice, this building actually uses wood for the mullions of its glazed facade.
Overall, this building has many nice features. For example, there is a beautiful solid masonry wall theme and curved light bands throughout all floors. In addition, it proudly sports a (slightly oversized) “LEED Gold” plaque close to the central atrium. In the context of its materiality and claim to resource efficiency, it is perfectly justified to find the mullions for all glazed walls made of glulam.
These vertical mullions span only from floor to floor, so wind loads shouldn’t be too high. What surprised me was that the glazing is actually supported by aluminum “mini-mullion” profiles, which in turn are attached to the glulams (see images left and below for detail). While I am sure there was a reason for doing it this way, I believe this is not necessary. As shown in one of the images below, curtain wall manufacturers (Kawneer in this example) make profiles that can directly be screwed into a supporting mullion. In that case, the entire structural support would be provided by the glulam and the aesthetics (and manufacturing) would be simplified.
Since these wood-glass facade systems are a bit more common in Europe, manufacturers over there have solved some of the tricky details already. For example, the connection between horizontal and vertical mullions can be done very elegantly using Knapp’s hidden Ricon connector (see image below).
In case you are in need of arguments for using wood for curtain walls or glazed facades, consider these:
- Aluminum has far higher embodied energy than wood. Also, wood can be harvested from sustainable sources.
- Wood mullions can reduce problems with thermal bridging and condensation.
- Wood mullions look good and give a warmer appearance than aluminum.
- Kawneer 1600 System – Going by the drawing above, their screw-on option is not marketed for use with wood. But there shouldn’t be a reason why it wouldn’t work.
- Alcoa AA 100 – A similar system by Alcoa.
- Knapp connections – Their Ricon connector is perfectly suited for connecting wooden horizontal and vertical mullions in a hidden “snap-in” application. (North American distributor: Stafast).
- Fassaden window systems – This company looks like a European import (located in PA) and offers complete wood-glass facade systems of many sizes. Look for technical details on their website. They also offer a wood clip-on cover as an option.
- Deerfield Academy Natatorium – Another wooden structure by SOM in the same location.