“Two eight five two, six over six, seven eighths muntins, four and nine jamb, with three and a half flat casing… four times.” This is what I said to Mary as she typed in the estimate—without skipping a beat. While this dialogue would be foreign to anyone outside of the fenestration industry, I bet it made perfect sense to most of you.
Not only is dimensional accuracy important, but so too is how the dimensions are interpreted. Some sizing interpretation is pretty clear—for example, muntin bar width. However, window “call-out sizing” can be interpreted in several different ways, and this is an opportunity for error.
The architect, purchaser, manufacturer and even the framer must interpret the call-out size exactly the same way without making any assumptions. Window frame material, manufacturer, and sometimes even region can define the call-out system. This calls for proactive communication.
Let’s look at the four call-out systems.
Frame size—Logically, window size would measure (or specify) the overall width and overall height of the frame. This frame size call-out is probably the most easily understood and clearly communicated call-out sizing system. The dimensions are tangible and most easily converted to rough opening dimensions.
It can be subjective, though, such as clarifying if the subsill is included (on some all-wood windows) with the frame height. This is a common call-out system for just about any window frame material and operator type, but not exclusive.
Sash opening—The sash opening call-out is a traditional system, usually communicated in feet and inches. It is limited to wood hung windows.
I happen to love this system for three reasons. First, this was the first system I learned. It’s automatic for me as replacement targets are flooded with all-wood double hungs. Second, understanding the sash opening of a wood double hung is also helpful when sizing a replacement insert or replacement sash kit, although the height is measured slightly differently for each replacement type. Lastly the “standard sizing” for this system is very consistent, typically using round numbers, which makes sizing easier to remember.
Glass size—This call-out is a system used less frequently, but still very popular. This, of course, is not daylight, but actual glass. From what I’ve experienced, a glass size call-out (in inches) is usually in round numbers, which makes it easier. I’ve seen this used in wood and wood-clad for both hung and swinging window types.
Glass sizing is probably the least helpful dimension for a replacement contractor, but there are some patterns that start to make sense once you get used to a brand that uses this system. Also, conversion tables provided by manufacturers can lead to more useful dimensions such as one of the above.
Rough opening—A fairly common call-out for non-wood products, this is the required rough opening for a specific product. This is convenient for new construction but can easily cause a mishap in replacement if you’re not aware. Be aware also that this can be called out in feet and inches, or just inches, yet possibly written exactly the same way for each. So, “3060” could be interpreted as “3-feet, 0-inches by 6-feet 0-inches” or “30 inches by 60 inches”—a huge difference!
Deciding which call-out system to use is not a personal decision; it’s really compliance to the manufacturers’ systems. Consult with the manufacturer for each particular product because many manufacturers use more than one system based on product type and product material. Regardless, make sure all involved are on the same system from the very start.
Jim Snyder is an AAMA-certified FenestrationMaster and InstallationMaster who shares his years of installation field experience as an industry writer, speaker, trainer and project/product consultant for dealers and manufacturers. A member of various industry organizations, Snyder also is involved in instructional document creation and revision. Contact him at firstname.lastname@example.org.