I'm trying to figure out if I can bypass requirement for tempered glass.

I have 3 windows 40x69 ea, installed in a row separated by 1 1/2 inch material (2x8), all of this is installed in a rough opening in the front of the house. (most people have a bay/bow window there, in that rough opening, but the house I bought has these 3 windows)

The interior seat (sill) is only 15 inches from the floor.

2018 International Building Code (2406.4.3) specifies that tempered (safety) glass is needed if all these conditions exist:

  1. The exposed area of an individual pane is greater than 9 square feet (0.84 m2).
  2. The bottom edge of the glazing is less than 18 inches (457 mm) above the floor.
  3. The top edge of the glazing is greater than 36 inches (914 mm) above the floor.
  4. One or more walking surface(s) are within 36 inches (914 mm), measured horizontally and in a straight line, of the plane of the glazing.

Now I want to replace these 3 windows with possibly 5 windows to bypass rule (1) - 9sq ft area rule. By splitting that huge opening into 5 (instead of the current 3), the window glass pane area of each window could possibly be below 9 sq. ft.

Is this acceptable?

  • What problem is the safety-glass requirement posing for you? Mar 27, 2019 at 2:32
  • Just trying to ascertain if I can save money where possible... There are lots of projects to do in this house. I do want to meet codes though.
    – tino
    Mar 27, 2019 at 2:36

5 Answers 5


Some areas may allow you to apply a safety window film. I have only seen it on heritage houses where the original windows are essential to the character of the house but I hear it's common in commercial applications. It's worth looking into. As long as it is up to your local codes.

  • 1
    Thanks for this suggestion. I called Licence and Inspections and they do allow it in Philadelphia. This is a cheaper way to attain safety comparable with tempered glass.
    – tino
    Apr 5, 2019 at 0:46
  • Awesome I'm really happy that I helped you save thousands of dollars!!
    – Joe Fala
    Apr 5, 2019 at 1:28

No, it is not acceptable to use non-tempered glass, because the “seat” area is within 18” of the floor.

The Code doesn’t say the window sill must be directly above the walking surface or if it could be recessed (like a window seat), etc.

Plus, you don’t want to put family and friends in jeopardy by having them next to such a hazardous situation. (What If a child walked along the seat?)

Btw, this code requirement requires the homeowner to change immediately. It is not “grandfathered” in as compliant. (There are 2 items in the Code that require the homeowner to up grade immediately: 1) tempered glass, and 2) smoke detectors.)

  • I thought that all 4 conditions need to exist for it to become a requirement. Hence the idea to divide it into 5 casement windows so that not one single IGU panel is over 9sq ft. On a side note, on the outside the window is only a few feet from the ground level.
    – tino
    Mar 28, 2019 at 0:32
  • @tino No, any one of the conditions will trigger the requirement to replace with safety glass (tempered or laminated).
    – Lee Sam
    Mar 28, 2019 at 2:07
  • It explicitly says the word "all" in 2406.4.3 We ended up going with tempered glass costing us $3000 installed... for quality low-E/argon/thermal break... and transferable lifetime warranty (including breakage warranty) installed by a reputable company. We're getting 2 casements and picture window in the middle...it was the wifey :)
    – tino
    Apr 5, 2019 at 0:53
  • @tino Ouch...expensive, but you can sleep at night. Happy wife, happy life.
    – Lee Sam
    Apr 5, 2019 at 3:55

I would suggest instead use sealed units made for patio doors. That 69 x 40 is very close to the size patio door used in condos, where you have a step over sill between the room and the balcony. Since you are buying a standard size unit, you get the prices of mass production instead of a custom made sealed unit.

If your climate permits non-sealed units, you can often get glass units that been replaced. These units are often free or very cheap. With work you can split the two panes sliding a putty knife, or trim pry-bar in the seal.

(I ahve a stack of 70 39.5" x 66" x 5/32" that I got for $50. Idea was for a green house)


ALL FOUR REQUIREMENTS HAVE TO BE MET OR YOU DO NOT TEMPER. If the window is a double hung then the 9 sq ft rule only applies to the bottom sash. Even if the bottom sash is larger than 9 sq ft then ONLY the bottom sash needs to be tempered. You also have the option of installing an oriel single hung so that the bottom sash is smaller than the top sash and falls under the 9 sq ft rule. Your windows do NOT have to be changed to meet new codes for tempering. If you replace the old window then you have to adhere to the new requirements.


If the bottom edge of glazing is 3" or more higher than the seat then you may be exempt? The requirement seems to be: The bottom edge of the glazing (not the seat) is less than 18 inches (457 mm) above the floor. 2018 International Building Code (2406.4.3)

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