Curtain Walls, Storefronts & Windows - Tech Tips Published

First the comparison is excellent, you do a very good job at analyzing what you approach.

I wish that you would expand the December issue to include “Window Walls” in addition to the others – there is a great deal of misunderstand in the profession about CW versus WW

Thank you

Steve Falk

Stephen H. Falk, emertius aia, ccs, csi, scip
Falk Associates, Inc.

Thank you for contributing your comments. I believe you make a good point. We did not consider Window Wall as another option that needed to be discussed. This is not a term that we see our clients using, although, I can certainly see the need to address the issue.

I have seen Window Wall refer to several different things. It may mean ribbon windows that are common in speculative office buildings. It may mean a multiple windows filling a large opening in a residence. And it is sometimes used, incorrectly in my opinion, to mean curtain wall. I searched the internet and our construction dictionaries. I found two different definitions in our construction dictionaries:

Windowwall: The opening in a wall surface which contains a window assembly or wall of assemblies.

Window Wall: A type of curtain wall, usually composed of vertical and horizontal metal framing members containing fixed lights, operable windows, or opaque panels or a combination thereof.

The dictionary with the second definition did not shed any light on what distinguishes a Window Wall as a type of curtain wall. The definition of curtain wall was essentially the same. Terminology is one of the principal causes of confusion in this industry. Depending on the region of the country, Window Wall and curtain wall could be interpreted as different things. The major metal fenestration manufacturers do not offer Window Walls as a product or system.

Considering the term itself, Window Walls should be punched openings within a single floor of a building, akin to windows. When multiple windows are joined to occupy all or nearly all of a single wall in a room, Window Wall may be an appropriate description. However the windows are still fitted into an opening within the exterior wall rather than forming the wall itself. This is consistent with the wood fenestration manufacturers' illustrations of residential Window Walls.

Depending on the scale of the opening, the Window Wall may be created using windows, storefronts, or even curtain walls. Curtain wall framing could be used for the larger scale visual appearance or to meet the span rating required for the opening. But the framing would still be limited to an opening within a single floor, rather than spanning multiple floors.

I appreciate this opportunity for additional discussion. I hope you continue to share your thoughts and experiences with us.

I'm glad that Steve brought up the issue of window wall, but I was hoping the answer would be a direct refuatation that such an animal exists. We have had contractors, clients, and some of our own architects insist that we include a specification section for "Window Wall." We (the spec department) have resisted this, based on the fact that the manufacturers rarely, if ever, call their products by that name. As David mentions, the term seems to apply to many different things, and once we figure out what the contractor, designer, or owner is talking about we write the proper specification. We have made some effort within our firm to educate the designers that "window wall" does not exist. Sometimes, however, resistance is futile.

Though your article did not address this issue, I think your response to Steve's question does cover it, and I appreciate that. Again, though, I would like to see us all agree that we should not be using the term.

Linton, I am glad you confirm that there is no consensus for what a "Window Wall" may be. Like you, we try to steer our clients away from this term because of the confusion it tends to create. We agree "Window Wall" should not be used on construction drawings or in the specifications.

Just recently came across your discussion while searching on another topic and thought I would add my two cents. My comments come from the perspective of a façade consultant. I’m sorry to report that in the façade industry, the term window wall does have a specific meaning and is distinctly different from a curtain wall system.

Window wall generally refers to a building enclosure system that is installed between the floor slabs of a building. The floor slab edges may be left exposed or may be covered with a cladding element (i.e., a slab edge cover). On the other hand, a curtain wall system is generally suspended from and spans outboard of the floor slab edges. Window wall systems have found favor in residential condo and apartment projects due to the solid floor to floor barrier formed by setting the wall system between the floor slabs.

Other than the slab edge covers, the two systems are designed in similar ways and utilize many of the same components. The performance requirements for the two systems can be identical. So your curtain wall specification can just as equally apply to a window wall project as long as the slab edge cover (if, required) is defined.

My believe is that the term “window wall” originated when fabricators took their standard window units (fixed and operable) and ganged them together using a continuous starter sill on top of the slab and a continuous head track mounted to the underside of the slab above. Literally, they formed a wall system out of individual window units. The head track (similar to the stack joint of a unitized curtain wall system) is used to absorb thermal movements of the window wall units as well as building structure deflections.

Today, the window wall system can comprise the same framing elements used in the construction of unitized curtain wall systems. You will also run into “hybrid” systems that combine the virtues of the two wall types.

Hope this helps clarify the differences between window walls and curtain walls.