Field Notes

Can You See Me Now?

By Chuck Knickerbocker

Assuming, for the purposes of this discussion, that most custom curtainwall and/or window projects will require visual mock-ups, some of us involved in the process aren’t always sure what we’re shooting for. This topic came up at a recent conference, and it bears some further development. The original conversation started out about glass samples and how to view that glass on the job, but we might want to broaden it to involve the framing that will support the selected glass.

First, let’s consider the glass. I think all of us can agree that the standard 12-inch by 12-inch glass samples from the glass supplier, when viewed in the sample room, aren’t going to be representative of how the glass will appear in actual service life. When placed on the outside of a building, lighting conditions will be different. If you don’t believe that, try getting your summer tan started under the florescent lighting in the office, as opposed to going outside and getting some rays the way Mother Nature intended.

That begs the question: can you take the samples outside and view them? And, would the result be representative of the aesthetics of the glass? The answer to both is no, because when the glass is on the building, the inside lighting of the occupied space combined with exposure to the sun and different cloud conditions will affect the appearance of any glass, irrespective of its thickness, coating(s) and/or construction.

How then would you mimic those conditions? Usually, the best way is to get actual project-sized glass and mount it in a sample wall that has an interior space, closed off from the back, that’s lighted similarly to replicate the project’s interior space conditions. You may need to engage the lighting consultant to re-create these conditions, and do that construction for both the vision and the spandrel areas, if you employ both glass types.

It also helps if the visual mock-up is on a turntable, so that you can view the glass from different elevations, mimicking the project’s elevations. If time permits, this method also allows the chance to view the samples under different weather and cloud conditions. Gray, overcast and sunny, clear skies might surprise you as to how different a glass sample will appear. And don’t forget to view the glass at night. Turn the lights on, look at the glass and see if it’s what you expected in appearance. Be sure to view it with the interior lights turned off, too.

While you’re at it, if there’s any question as to which glass to select, getting samples of each type under consideration can give the owner and architect another opportunity to see the glass possibilities in “real world” conditions.

It’s a bit more problematic if the visual mock-up must also evaluate the framing. Using a standard frame isn’t as much of a concern, since materials can be procured quickly, fabricated and installed. However, in custom walls where new shapes are required, allowing time for tooling and production runs has to be reconciled against potential changes the visual mock-up may require to project schedules. The choice is between mimicking the custom extrusions with formed material in combinations with other extruded shapes or waiting for the actual production of the new shapes. Both paths will have an impact on schedules. If changes to the extrusions are considered after the visual mock-up, should the previous dies to be so much scrap? What, if any, performance mock-up and/or production runs have started for the job? It’s a hornet’s nest.

When specifying visual mock-ups, please include the conditions upon which the sample wall is to be viewed and state the goals that will be met by performing the mock-up. One, it will give those of us on this side the chance to accurately estimate the cost. Two, we can develop realistic schedules of how the visual mock-up will impact the job if changes are to be considered as the result of the mock-up. And three, it will also allow all the players—owners, architects and subcontractors—to actually see what the wall will look like at the end of the job earlier in a project’s life.

This column was adapted from Chuck Knickerbocker’s August 29, 2019, USGNN™ “Field Notes” blog post.

Chuck Knickerbocker is the curtainwall manager for Technical Glass Products (TGP), a supplier of fire-rated glass and framing systems, along with specialty architectural glazing products. With more than 35 years of curtainwall experience, he has worked successfully with numerous architects, building owners and subcontractors from development of schematic design through installation. He can be contacted via email at

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