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How to Measure the Height of an Emergency Escape and Rescue Opening

jar546

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When installing emergency escape and rescue openings (often referred to as egress windows), IRC Section R310.2.3 specifies that the bottom of the clear opening must be no higher than 44 inches above the floor. Understanding exactly where to measure this height is critical to meet code compliance and safety requirements.

Critical Measurement Point: Bottom of the Clear Glazed Opening​

IRC Section R310.2.3 requires that the measurement be taken to the bottom of the clear, openable portion of the window—specifically, the lowest edge of the glass (glazing) itself. This height should not be measured to the bottom of the window frame or sash frame, as those parts do not contribute to the actual openable escape area. Instead, only the clear, unobstructed glazed area that provides the path for escape and rescue access should be considered.

To clarify:
  • Do not measure to the bottom of the frame or sash around the glass.
  • Measure to the lowest part of the openable glass (glazing), as this area provides the actual escape path.

Why This Distinction is Important​

This requirement is intended to ensure that the clear opening is low enough to be accessible without obstruction by additional framing, making escape and rescue easier.

Summary​

  • Code Reference: IRC Section R310.2.3
  • Measurement Point: Measure from the floor to the bottom of the clear, openable glazed area only—not the window frame or sash.
  • Purpose: Provides unobstructed, accessible space for emergency egress and rescue.
 
R310.2.2 says the net clear opening dimensions shall be the result of normal operation of the opening. It doesn’t say anything about glass.
In the 2021 IRC, this was in section R310.2.3.
In the 2024 IRC, this was moved to R319.2.3

This is the official opinion of the ICC as published in their Premium Answers. The intent is for a firefighter in full gear who may have to break the glazing to gain entry can easily get in and out, just as a person on the inside would have the ability to get out.

CC Opinion:​

This opinion is also applicable to the 2024 IRC.

In general, the net clear opening and minimum opening dimensions for an emergency escape and rescue opening are intended to provide a clear opening through which an occupant can pass to escape a building, or a firefighter (in full protective clothing with a breathing apparatus) can pass to enter a building for rescue or fire suppression activities. As such, the net clear area is the actual opening size, not the size of the window, including the window frame.

As stated in the 2021 IRC Section R310.2.3, the bottom of the “clear opening” shall not be greater than 44 inches measured from the floor. Therefore, the required 44 inches would be measured to the actual glazed opening and not to the bottom of the window frame.
 
In the 2021 IRC, this was in section R310.2.3.
In the 2024 IRC, this was moved to R319.2.3

This is the official opinion of the ICC as published in their Premium Answers. The intent is for a firefighter in full gear who may have to break the glazing to gain entry can easily get in and out, just as a person on the inside would have the ability to get out.

CC Opinion:​

This opinion is also applicable to the 2024 IRC.

In general, the net clear opening and minimum opening dimensions for an emergency escape and rescue opening are intended to provide a clear opening through which an occupant can pass to escape a building, or a firefighter (in full protective clothing with a breathing apparatus) can pass to enter a building for rescue or fire suppression activities. As such, the net clear area is the actual opening size, not the size of the window, including the window frame.

As stated in the 2021 IRC Section R310.2.3, the bottom of the “clear opening” shall not be greater than 44 inches measured from the floor. Therefore, the required 44 inches would be measured to the actual glazed opening and not to the bottom of the window frame.
This is not related to the bottom of the window frame. The code says clear opening and specifies that the clear opening is the result of normal operation, not breaking glass. The definition of emergency escape and rescue opening doesn’t even require glass.
 
This is not related to the bottom of the window frame. The code says clear opening and specifies that the clear opening is the result of normal operation, not breaking glass. The definition of emergency escape and rescue opening doesn’t even require glass.
It is specific to glazing and confirmed as the intent of the code, hence the word "net." Would you like to submit for a formal opinion, using this as an example that you don't agree with?
 
It is specific to glazing and confirmed as the intent of the code, hence the word "net." Would you like to submit for a formal opinion, using this as an example that you don't agree with?
Enforcement that is consistent with the language in the code is important to those of us using the code and required to comply with it. The word net is not described as an opening through broken glass. It is described as the result of normal operation. Normal operation would mean opening the window, not breaking the glass.

If the formal opinion means the code requires breakable glass and an opening of minimum dimensions through the remaining opening, I have little use for it unless it can direct me to where the code says that.
 
Enforcement that is consistent with the language in the code is important to those of us using the code and required to comply with it. The word net is not described as an opening through broken glass. It is described as the result of normal operation. Normal operation would mean opening the window, not breaking the glass.

If the formal opinion means the code requires breakable glass and an opening of minimum dimensions through the remaining opening, I have little use for it unless it can direct me to where the code says that.
I agree with you on the verbiage. The intent is clarified in the ICC opinion which you are now aware of.
 
I’m confused. So Jeff, are you saying that the measurement is to the glass? That would be with the window in the closed position? That is because a fireman might break the glass to get in rather than open the window? Is that what you are contending?

Firemen don’t just break the glass, they rip out the frame that held the glass. The 44” is measured to the floor and the fireman is outside. The O in EERO stands for opening.
 
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I’m confused. So Jeff, are you saying that the measurement is to the glass? That would be with the window in the closed position? That is because a fireman might break the glass to get in rather than open the window? Is that what you are contending?

Firemen don’t just break the glass, they rip out the frame that held the glass. The 44” is measured to the floor and the fireman is outside. The O in EERO stands for opening.
That is exactly what the ICC is saying.
 
This is what I have to work with and apparently it is different from what you have to work with:

R310.2.2 Window sill height. Where a window is provided as the emergency escape and rescue opening, it shall have the bottom of the clear opening not greater than 44 inches (1118 mm) measured from the floor; where the sill height is below grade, it shall be provided with a window well in accordance with Section R310.2.3.

That's as straightforward as it gets. Why you would ask the ICC to clarify that bit of code escapes me. And by the way, it often depends on the day of the week and the time of day as to how the ICC will respond.

While on the topic of EERO I wonder about the Grade Floor Opening reduction to five square feet from 5.7 square feet. I do not see an advantage that having the exterior grade no more than 44" below the sill presents that would allow a reduction in the net free opening size. fatboy ain't getting out any easier ... in fact it might be tougher for the fatboy.
 
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I can't enforce an ICC opinion or interpretation. I have to go by what the language of the code says. Not only that, the ICC interpretation you cite is contrary to what the ICC wrote in the 2021 IRC Commentary. Commentary for R310.2.1:

The net clear opening area and minimum dimensions
are intended to provide a clear opening through which
an occupant can pass to escape the building or a fire
fighter (in full protective clothing with breathing apparatus)
can pass to enter the building for rescue or fire
suppression activities. Note this is the clear opening
size
, not the size of the window.

This does not say that it's the glazed portion of a sash. And the code has never expected residents to break the glass to escape from their bedrooms.

Since the emergency escape windows must be
usable to all occupants, including children and guests,
the required opening dimensions must be achieved by
the normal operation of the window from the inside
(e.g., sliding, swinging or lifting the sash). It is impractical
to assume that all occupants can operate a window
that requires a special sequence of operations to
achieve the required opening size. While most occupants
are familiar with the normal operation by which
to open the window, children and guests are frequently
unfamiliar with any special procedures that may be
necessary to remove or tilt the sashes. The time spent
in comprehending the special operation unnecessarily
delays egress from the bedroom and could lead to
panic and further confusion. Thus, windows that
achieve the required opening dimensions only through
operations such as the removal of sashes or mullions
are not permitted. It should be noted that the minimum
area cannot be achieved by using both the minimum
height and minimum width specified in Section
R310.2.2 (see Commentary Figure R310.2.1).

The accompanying figure shows the measurements to the sash opening, not to the glazed area within the sash:

1729961930954.png
 
As Jay said in post #4, the code doesn’t even require glazing. It could be a small solid door/hatch.
In fact, in a very temperate climate the sleeping room might not be enclosed with a window or door at all - - an “opening” can just be a fixed opening.

In Los Angeles, they’ve determined that there is also a minimum height at operable windows at upper stories, and they measure it from the lowest point of opening (top of sill). This is because the sill functions as a type of guardrail when the window is opened.

 
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actual glazed opening
If the use of that phrase is the only reason you are talking about breaking glass, I think you are misinterpreting it. Overall, the text you quoted in post #3 is more consistent with the idea of clear opening as per the other references above.

and not to the bottom of the window frame.
Window frame would be the fixed jambs of the window within with the sash sits, and that is different from sash frame. So this language just clarifies that the clear opening is smaller than the rough opening into which the window frame is installed at the time of construction.

Cheers, Wayne
 
What Ben posted is what we enforce,
That's what I was taught,
That's the way my subs installed it when I was in construction and it passed inspection,
That's the way the 2021 IRC Commentary sez "From the floor to the bottom of the clear opening"

We deal with a lot of different vinyl windows that have a water guard like in Ben's pic.
Old wood window seals did not have this water guard piece, you usually would have window stool there to measure from.

I think we'll just keep doing it wrong!
 
The proper term is clear opening:

R310.2.2​

The minimum net clear opening height dimension shall be 24 inches (610 mm). The minimum net clear opening width dimension shall be 20 inches (508 mm). The net clear opening dimensions shall be the result of normal operation of the opening.

R310.2.3​

Emergency escape and rescue openings shall have the bottom of the clear opening not greater than 44 inches (1118 mm) above the floor.

It has nothing to do with breaking the glass.....
 
If the use of that phrase is the only reason you are talking about breaking glass, I think you are misinterpreting it. Overall, the text you quoted in post #3 is more consistent with the idea of clear opening as per the other references above.
The words I posted are copy and paste from the ICC, not my opinion.
 
The words I posted are copy and paste from the ICC, not my opinion.
Right, but the phrase "actual glazed opening" in the context of the answer and the code language in question means "the actual opening that is occupied primarily by the glazing when the window is closed". If the ICC intended anything else by that language, it would be in error, so I doubt anything else was intended.

Cheers, Wayne
 
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The words I posted are copy and paste from the ICC, not my opinion.

Yes, and the words make no sense. If you read the words literally, they say that in a wood double-hung window, the glass opens but the wood sash stays in place.

That obviously doesn't make sense. I'm going with the way we've been doing it since escape/rescue openings first came into the codes 50 years ago.
 
Right, but the phrase "actual glazed opening" in the context of the answer and the code language in question means "the actual opening that is occupied primarily by the glazing when the window is closed". If the ICC intended anything else by that language, it would be in error, so I doubt anything else was intended.

Cheers, Wayne
Yes. I do not agree with their interpretation because it does not match the verbiage in the codes.
 
In post #12, I referenced a City of LA requirement that a normally opened window provide a sill (incl. waterstop) that functions as a 42” guardrail.
If they were to also measure to glazing for max 44” AFF EERO, that would leave less than 2” for window sash width.
I say ignore the glazing focus on the operable opening.
 
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