The advantages of having the curtain wall mullions on the EXTERIOR of the building.

Since Contravex is about so much more than just Bitcoin, child-rearing, liqueur fashioning, small “p” politics, big “P” politics, movie reviews, travels, travails, or the latest overpriced shit I bought,i let’s talk about architecture and engineering! Specifically let’s talk about curtain walls, which, weirdly, I happen to know a thing or two about.ii

While in no way commonly conceived, much less commonly implemented, in the commercial, institutional, or multi-family construction industries today, the “backwards” approach of placing the mullion of the curtain wall system on the EXTERIOR of the building is not only incredibly rare, but in fact has some striking advantages over the conventional interior placement of the mullions.

Such advantages include :

1. Parallax visual effectiii
2. Anchoring for window washers on skyscrapersiv
3. Reducing interior visual impact while enhancing exterior visual impactv
4. Maintaining strengthvi
5. Minimising physical intrusions into interior space, maximise valuable interior square footage
6. Minimising radiant heating and cooling into interior, improve occupant comfortvii

Though exterior mullions are not without their attendant disadvantages :

1. Thermal bridgingviii
2. Combustibility issues if using wood or fibreglass projectionsix
3. Premature weathering if using wood or fibreglassx
4. Manufacturer lead times and costsxi
5. Trade abilities and competencies with customised curtain walls are hen’s teethxii

See ? More advantages than disadvantages. Democracy wins!

Now where were we…
___ ___ ___

  1. Fine, if you’re really curious, the recent list of overpriced shit I’ve bought includes a retired-florida-jew-esque Paul Smith track suit, a couple Comme Des Garcons t-shirts (with the adorable little hearts and fait au Japon!), some NIKEiD Frees (left shoe says “LEFT,” right shoe says “RIGHT” just in case), two pairs of prescription Oakleys, and a pair of Starck-Mikli eyeglasses with blue-tinted nerd lenses as well as these dope “shoulder-inspired” double-hinges that mean they’re basically immune to being broken whenever I’m hit in the face, which as you can imagine happens with some regularity.

    A couple bigger-ticket items are heading this way in the next 6-9 months, some of which have been teased already, but all of which (coincidentally) have their roots in the 1970’s even though they’re all 2018 editions/interpretations thereof. Funny how that happens eh. Now where were we!  

  2. Reimagining the Metlife Building was but a glimpse. 
  3. Parallex is just a fancy word for the optical illusion wherein an object at rest appears to be displaced when the observer moves their position relative to the resting object. Mies’ Seagram Building accomplishes this effect with the use of exterior bronze I-beams, which act to reinforce the vertical curtain wall mullions. seagram bronze curtain wall mullions

  4. Don’t underestimate the impact that janitorial and maintenance managers have on the design of a new building. It’s actually a bit frightening at times, particularly on public projects where “all voices matter equally.” Not that skyscraper maintenance is anything to sneeze at. There are plenty of tall buildings that have permanent window washing crews that start at the top, work their way to the bottom, and start all over again – year in and year out.  
  5. Compare a typical skycraper interior :

    typical skyscraper interiorWith Mies’ Seagram Building (a building I inexplicably spend an inordinate amount of time thinking and reading about despite my general detest for modernism and too-tall buildings, possibly because it featured a gorgeously detailed stick-built curtain wall system whereas practically every skyscraper since has used commodity unitised systems, or possibly because the heart just loves what it loves) :

    seagram building interior

  6. Curtain walls only handles wind load – much like a shower curtain acts only as an elemental barrier, not as a structural system. By definition, a curtain wall is suspended off the edge of the slab (floor plate) and so handles no dead load. A window wall, by contrast, while it can be made to look like a curtain wall from the exterior, is in fact gravity suspended and rests upon the edge of the floor plate. You can usually tell them apart from the depths of their vertical mullions : curtain wall systems are 6″+ whereas window wall systems might be as shallow as 3″.
  7. Conductive heating and cooling are unaffected by the placement of the curtain wall mullion on either the interior or the exterior, all else being equal, but the radiative effects are magnified by the intrusion of a metal mullion (usually aluminum) into the interior.
  8. Where do you put the thermal break ? While plastic can be used in the neck of the system between the two glazing panels, a fibreglass pressure plate has nowhere to go.  
  9. kengo kuma one omotesando exterior

    One Ometasando in Tokyo by Kengo Kuma, built in 2003 for LVMH office and retail, used exterior wood mullions made of laminated larch that would’ve been prohibited by the local fire codes had Kuma obtained an exemption by installing an exterior sprinkler system.

    kengo kuma one omotesando curtain wall detailThe temperate climate of Tokyo allowed for only double-glazing. Kuma also contrasted the prominent and pronounced vertical fins with structural silicone glazed (SSG) horizontal seals. SSG was a technology not available to Mies a half-century ago but is widely used in both two-sided applications as seen here as well as four-sided applications seen commonly on skyscrapers.

  10. This weathering may not even be undesirable. Modern buildings don’t typically shy away from the fact that they have finite lifespans. This isn’t the First Bank of the United States we’re building here. Those days are over.
  11. These are not off-the-shelf systems and are priced accordingly.
  12. You’ll note that both featured projects hereabove were completed in global mega-cities for clients intent on leaving a legacy no matter the cost. You may be interested to know that the Seagram Building, owned by the run-rumming Canadian family that made out like bandits during Prohibition, was the most expensive building ever built when it was completed in 1958.

    N.B. This distinction obviously precludes the Pyramids at Giza et al. because how much does a slave army even cost ?  

2 thoughts on “The advantages of having the curtain wall mullions on the EXTERIOR of the building.

  1. […] of greater sinuousness. As to the facade, the continuous balconies around the exterior preclude proper curtain wall that would span from slab edge to slab edge, and in so doing vastly simplifies the window wall […]

  2. […] external curtain wall mullions – rendered here in steel instead of the OTT bronze of the earth-shattering Seagram Building […]

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