Design Architecture Should Architects Say Bye to the Bay Window? By Lloyd Alter Design Editor University of Toronto Lloyd Alter is Design Editor for Treehugger and teaches Sustainable Design at Ryerson University in Toronto. our editorial process Facebook Facebook Twitter Twitter Lloyd Alter Updated October 11, 2018 ©. Platform 5 Architects Share Twitter Pinterest Email Design Tiny Homes Architecture Interior Design Green Design Urban Design Architect Elrond Burrell points to Studio MM’s website, where they extoll the virtue of the modern bay window, defined as “a window built to project outward from an outside wall.” She calls them “beautifully modern and cozy,” showing a lovely box bay on a renovation in London by Platform 5 Architects. But are they? I have a bay window in my home, albeit not modern, but also not cozy. The increase in surface area and the fact that it is cantilevered out with an uninsulated floor makes it impossibly cold in winter. And mine has storm windows inside and out. Lloyd Alter/CC BY 2.0 After the tweets started flying I remembered the one that I photographed a few years ago, on Diamond and Schmitt’s Bahen Centre at the University of Toronto. Lloyd Alter/CC BY 2.0 I just kept looking at this and thinking it makes no sense; not only is it all single glazed held together with metal brackets and caulk, which is bad enough, but it has those wicked cantilevered glass radiator fins just to make it extra cold. The only way it could be habitable is if it is pouring heat out of that grill that you see the underside of here. Lloyd Alter/CC BY 2.0 At the time I wondered, are architects who do these kinds of things even thinking about energy? About comfort? Or are they just thinking about how cool that cantilevered glass looks? © Coupdeville Architects via Culmax Really, the same thing can be said about many of the residential box bays that are so popular. They look terrific, but dramatically increase the surface area and heat loss through the glass. They are often single-glazed because it is really hard to join double glazed units without a heavy frame. If they are ever cozy, it is for a very small portion of the year. Elrond Burrell commented on the MM site: Unfortunately, it’s a vernacular that is in serious need of updating. Putting a hole in your thermal envelope is one thing (windows and doors) and it can be done well with high-performance components. But pushing that hole out beyond the thermal envelope makes it perform even worse for heat loss, energy use, comfort and hygiene. So, looks good, but performs very badly! Perhaps it is time to say ‘bye to the box bay window- it looks good but we can’t afford it anymore.