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Industry Resources: Ask The Expert FAQ

Q. I need advice on the type of glass to use in a residential elevator shaft. The openings are punched and will have removable stops. Can we use tempered glass or should we use a heat strengthened laminated glass? (Additional information: There are four (4) stories connected and this is an interior application. The glass panels are approximately 42” x 102”. Stairs surround the exterior of the elevator shaft and there is no fire resistant rating for the elevator shaft wall.)

A. Since you have indicated there is no fire resistance rating requirement for the elevator enclosure, the requirements for safety glazing would govern. Please note however that the only scenario I am aware of in which the walls of the elevator hoistway enclosure are not required to be fire-resistant rated is if the elevator hoistway occurs in an atrium that is separated from the remainder of the building, as required by the IBC.

Basically, the IBC will require all of the glass in the enclosure to meet the requirements of ANSI Z97.1 or CPSC 16 CFR Part 1201. This is glazing that is commonly referred to as safety glazing, and tempered glass is most commonly used to meet it.

Also note that the glass in the hoistway doors must meet the more stringent Class A requirements of ANSI Z97.1 or Category II of CPSC 16 CFR Part 1201. It must be a minimum of 1/4 inch thick, with a minimum size of 24 sq. inches and a maximum size of 85 sq. inches. In some cases this requirement is met using tempered glass, and in others it is met by laminating two lites of tempered glass together.

The specific requirements of the 2015 IBC are given below:

2409.2 Glass in elevator hoistway enclosures. Glass in elevator hoistway enclosures and hoistway doors shall be laminated glass conforming to ANSI Z97.1 or CPSC 16 CFR Part 1201.

2409.2.1 Fire-resistance-rated hoistways. Glass installed in hoistways and hoistway doors where the hoistway is required to have a fire-resistance rating shall also comply with Section 716.

2409.2.2 Glass hoistway doors. The glass in glass hoistway doors shall be not less than 60 percent of the total visible door panel surface area as seen from the landing side.

2409.3 Visions panels in elevator hoistway doors. Glass in vision panels in elevator hoistway doors shall be permitted to be any transparent glazing material not less than 1/4 inch (6.4 mm) in thickness conforming to Class A in accordance with ANSI Z97.1 or Category II in accordance with CPSC 16 CFR

Part 1201. The area of any single vision panel shall be not less than 24 square inches (15 484 mm2) and the total area of one or more vision panels in any hoistway door shall be not more than 85 square inches (54 839 mm2).

Q. We are replacing two (possibly three) pieces of Obscure Laminated Wire Glass at the hallway entrance to an elevator hoistway. The building, where the replacement glass is required, was erected around the turn of the 20th century. With this said, we are unable to locate section 719 of the ANSI code that pertains to identifying the requirements necessary to determine if this glass needs to meet a particular fire-rating code; in addition to the laminating glass standard pursuant to ANSI Z97.1.

A. You have raised an interesting question. If the building was constructed around the turn of the 20th century (early 1900's), it predates both the fire rating codes and the requirements for safety glazing in hazardous locations. Codes for fire rated construction did not begin to be put into place until around 1920 and the requirements for safety glazing in hazardous locations were not implemented until the early 1970's. That being said, the current codes would require the replacement glazing to meet the requirements of the current code for new construction.

This includes, as you indicated, the use of laminated glass that meets Class A of ANSI Z97.a or Category II of CPSC 16 CFR Part 1201. Please note that these are requirements for resistance to human impact and NOT fire rating. Perhaps this is why you have not been able to locate the required fire ratings - they are not located in ANSI Z97.1 or CPSC 16 CFR Part 1201. The requirements for this particular application have been in a state of flux over the last several editions of the model codes.

The fire rating requirements for this glass would depend upon the edition of the IBC that is being enforced, along with some particulars specific to the installation. These particulars include: the number of stories connected by the elevator hoistway shaft; the total height of the building (in feet); the location of the entrance to the hoistway relative to the building entrance (on the same level or on different levels); and the location of the entrance of the hoistway relative to the hallway (elevator opens directly into the hallway vs. opening into an elevator lobby that is off of the hallway).

Q. I am replacing the glass only of a double pane glass window that is located 17-1/2 inches up from the floor to the bottom of the window. The height of the glass is 58-1/2 inches and width is 16-1/2 inches. The window is not next to a door. Does the replacement glass need to be safety glass?

A. The glazing would be required to be safety glazing IF the bottom of the window is less than 18 inches above the floor, the top is more than 36 inches above the floor and the glazing is located within 36 inches of a horizontal walking surface such as a floor.

The fourth criteria for whether or not the glass is required to be safety glazing is its size. If ALL of the following conditions occur, then the glass is required to be safety glazing:

  • The size of the glazed opening exceeds 9 sq. ft.
  • The bottom of the glazing occurs within 18 inches of the floor or horizontal surface below.
  • The top of the glazing occurs at least 36 inches above the floor or horizontal surface below.
  • There is a walking surface within 36 inches of the glazing.

Based on the information provided, at least 2 of the 4 criteria have been met. Assuming the top of the glazing is at least 36 inches above the floor, the remaining criteria is the size of the glazed opening (i.e. is the glazing > 9 sq. ft. in size?). In this example, the size of the glass is approximately 6.25 sq. ft - which is less than 9 sq. ft. Therefore safety glazing is not required - unless the glazing is near a door, stairway, ramp or pool, tub or spa.

Q. Our suppliers tell us the glass has to be at least 12” across the diagonal measurement in order for it to go through the tempering oven without falling through the rollers. What are the code requirements for a door that has individual panes too small to
be tempered?

A. If the 3" sphere can pass through the glazed opening in their door, then safety glazing appears to be necessary, according to IBC 2006 and 2009.

A follow up question, to their glass distributor, could be this: Would their laminated glass comply with safety glazing requirements, such as impact resistance testing mentioned in section 2406.1.1 of the IBC codes above? If yes, then could they make laminated glass the size needed for
their opening?

Also, although the model codes (IBC and IRC) have an exception to the safety glazing requirements for glass in doors that is less than 3“ in diameter, the reason for that exception is not due to the difficulty of tempering such a small piece of glass. The reason for that exception is the reduced likelihood of the limb of a body breaking and passing through such a small piece of glass.

With regard to lights of glass that are less than 12” across the diagonal measurement, but greater than 3 “ in diameter, there are other types of glass that can be used to meet the safety glazing requirements of the IBC and IRC. Specifically, glass that complies with CPSC 16 Part 1201 Category Class II or ANSI Z97.1 Category Class A can be used. This criteria is most commonly met using tempered glass, but it may also be met using laminated glass. In some instances, various types of plastic glazing may also be used.

Q. The code book states if all other conditions are met, except the condition “exposed area of an individual pane is greater than 9 square feet” that safety glass is NOT required. Has this been amended since? (example a 3x6 single hung window where the exposed area of the bottom sash is not 9 square feet.)

A. With regard to whether or not lites of glass greater than 9 sq ft must be safety glazing - all of the criteria of the code (lites greater than 9 sq ft, within 36 inches horizontally of a walking surface, bottom edge within 18 inches vertically and top edge more than 36 inches vertically above the walking surface) must be met. If any one of those is not met safety glazing is not required.

Q. How do you meet code and have deck railings/balusters made of glass without an additional metal or wood rail on top?

A. Section 2407.1 of the 2009 and 2012 IBC contains an exception to the top rail requirement for glass guards. A top rail is not required on glass infill panels of guards on decks and other elevated walking surfaces when the assembly of glass infill panels and their vertical supports can resist the loads required for guardrails and the infill glass is laminated glass consisting of at least two lites of the same thickness and type of glass.

The loads required for guardrails is 50 pounds per linear foot, acting on the top of the panel, or 200 pounds concentrated load acting at any location on the panel.

This exception to the requirement for a continuous top rail is based upon the guardrail itself being able to resist the loads, and also the premise that the use of laminated glass of at least 2 lites of equal thickness and same glass type provides some redundancy within the system. Redundancy refers to the design strategy that if one element fails there is a back up. In the case of the glass infill panel, the second lite of equal thickness and the same type is considered the back up, should one lite be shattered.

Note that the glass infill panels would also be required to meet the criteria for safety glazing, per Section 2406.4 of the 2009 IBC and Section 2406.4.4 of the 2012 IBC.

Q. I don’t understand the wording in the code about door sidelites that are perpendicular to the door. If perpendicular, are they simply not required to be safety glass, if not required by some other hazardous location condition?

A. The 2009 and 2012 IBC exempts some glazing that is perpendicular to the plane of a door from being safety glazing, but not all. Basically, all glazing within a 24 inch arc of a door opening is required to be safety glazing unless both the door and glass in question are within a residential dwelling unit and the glass is not on the wall towards which the door swings, or one of the other exceptions for glass near doors applies. The concern is that glass in a wall perpendicular to a door that is in the wall toward which the door swings may be struck by the door or some hardware that is attached to the door when it is opened. Therefore, that glass must be safety glazing. Also note that this exception only applies in residential dwelling units. The glass in walls perpendicular to the door on either side of the door must be safety glazing if the glass is not contained within a residential dwelling unit. For example, if the window at the end of a hallway in a multifamily apartment building is within 24 inches of a door, it must be safety glazing, even if it is in a wall that is perpendicular to the door on the latch side of the door, and therefore not likely to be struck by the door when it is opened.

Q. Q. I have a movie theater that wants to install a glass railing in the second floor balcony with a 19” wall + 7” glass = 26” total. I think it needs to be at least 42” high, but 42” is too high for their patrons. What is the code on hand rails? Thanks for your help!

A. Please note that the requirements for handrails are quite different than for guards. This response assumes that the inquiry relates to the minimum height requirement for balcony guards.

IBC 2003 (and we don't think it has been amended with reference to this) does allow for theater balcony railings as low as 26" if sightlines would be obstructed by a taller rail. It is recommended that the company verify the applicable code and have the local building code enforcement person or inspector sign off on the design first, in writing.

Secondly, IBC-2006 (section 1013.2 ) refers to 42" for the minimum height of hand rail guards; however, the company should consult their local building official about a possible exception noted in section 1028.14. It is not clear if their application would qualify for this exception.

Also, code requirements do change from edition to edition. In this case, however, the provisions regarding guardrail height in areas of assembly seating (such as the balcony of a movie theatre) have remained somewhat consistent from the 2003 IBC to the 2012 IBC - although the section numbering has changed. In the 2012 IBC the height requirements are given in Section 1028.14.

Basically, the required height depends upon whether the guard occurs along or at the end of a cross aisle (a designated path of travel that is approximately parallel to the stage), at the end of an aisle (a designated path of travel that is approximately perpendicular to the stage) or between the seating itself and the stage. Assuming the balcony itself is more than 30 inches above the floor below, the following applies:

If the guard is along or at the end of a cross aisle then its required minimum height is 42 inches. A guard is not required along the cross aisles, however, if the back of seats on the front of the cross aisle (between the cross aisle and the stage) project more than 24 inches above the height of the adjacent floor.

If the guard is at the end of the aisle (basically the path the occupants take down the balcony to get to their seating in the balcony) then the required minimum height is 36 inches. This height must be maintained for the full width of the aisle. In addition, the distance from the nearest step to the guard rail must be such that that dimension from the top of the rail to the nosing of that step's thread is at least 42 inches. This basically means that if the stair is too close to the guard, the height of the rail itself will have to be raised.

Where the other two instances do not occur, and a guard height of 36 or 42 inches would interfere with the sightlines of the immediately adjacent seating, a guard with a minimum height of 26 inches is to be provided. Note that the minimum height of 26 inches is only permitted under these specific circumstances. In many instances of minimum height guard of 36 or 48 inches may be required to transition to a guard height of 26 inches to meet these requirements while providing a minimum obstruction to the theater goers sightlines.

Q. We are working on a project that calls for "laminated and tempered" as opposed to “annealed and laminated" or "heat strengthened and laminated." Can you explain the differences? Is there really that big a difference - why would a project call for it?

A. Annealed is standard glass, as it is formed after the molten glass is poured onto the cooling table. Both heat strengthened and tempered have been subjected to higher temperatures after the glass is formed. This increases the strength of the glass, with tempered glass being stronger than heat strengthened.

Laminated glass is formed by bonding two or more layers of glass together with a binding material, such as a PVC interlayer. It is also stronger than annealed glass. Project specifications that call for "laminated and tempered" are calling for the strongest type of glass layup available for a particular thickness of glass.

Is there a big difference? The answer is a resounding "Yes". Glass that is both tempered and laminated will not only be the strongest available for a particular thickness of glass, but the hazard associated with it shattering is greatly reduced. This is because tempering the glass causes it to break into small, less sharp pieces than annealed glass would if hit with the same impact. Also, the interlayer that binds laminated glass together also tends to bind shattered glass together if impacted. So that is a greatly reduced likelihood of injury due to impact with tempered and laminated glass than for any of the other possible types or combinations.

Why would a project call for laminated and tempered glass? There are code provisions for safety glazing that are often met by using tempered or laminated glass. We have discussed some of those in previous responses to "Ask the Expert". But the requirements for safety glazing can usually be met with either tempered or laminated glass, and does not require glass that has been both tempered and laminated. There are other possible reasons for the specifications calling for this particular lay up. They include resistance to design loads (including, but not limited to, wind load and impact loads).

It could be that the windows, storefront or curtain wall need safety glazing due to their locations, such as near an entrance and walking surfaces. It could also be that the project has overhead glazing conditions, blast resistance and areas needing impact resistance. This might be the cause for laminated glazing.

There should be a review of the contract documents (CD) and then evaluate how the building code affects or changes the information in these contract documents.

Q: I’m working on a job in a hotel that requires an exterior 20 minute fire rated door. Is there a problem with using polished wire glass on the door? Can polished wire glass be used on the interior/corridor side of the door and ¼ tempered glass be used on the exterior side of door?

A: There IS a problem using polished wire glass on EITHER side of the door. Refer back to the 2009 International Building Code section 715.4.7.4 - Safety Glazing where it says, "Fire-protection rated glazing installed in Fire doors in areas subject to human impact in hazardous locations shall comply with Chapter 24." Chapter  24 section 2406.4 states, "The following shall be considered specific hazardous locations requiring safety glazing materials, 1. Glazing in swinging doors, except jalousies."

Wire Glass IS NOT safety glass. It will not comply with the code. You should go to a supplier who can recommend alternative products, such as "Firelite".

I have seen many terrible injuries from wire glass over the last 25 years. When a body part goes thru the glass, usually a hand and arm, the person instinctively pulls the hand back. That action strips the skin and tendons and leaves the person with many years of surgical reconstruction and a lifelong injury.

Q: Is there a difference between AS 1 glass and AS 2 glass? I had forklift that needed a new windshield and I requested that AS 2 glass be used per the manufacturer’s instructions. AS 1 glass was used and the glass now has a 47 inch crack in it that no one can explain. The installer is telling me that there is no difference between AS 1 and AS 2 glass and that if he had installed AS 2 glass it would not have made a difference. There is no indication that something hit the glass; it hasn’t been stored in any extreme temperatures.

A: AS stands for American Standard. The number indicates the position in the vehicle where the glass may be used, based on its optical quality. AS1 is the clearest glass (at least 70% light transmission), is laminated, and can be used anywhere in a motor vehicle (typically just the windshield). AS2 is tempered with at least 70% light transmissions, and can be used anywhere except the windshield, and AS3 can be used in certain locations in certain vehicles (and can be laminated or tempered, and has less than 70% light transmission).

In the example you give (a forklift), this is an off-the-road vehicle where low speeds are typical. It is entirely possible that the forklift manufacturer does recommend an AS2 windshield since the “clearest glass” (AS1) may not be needed. I do not believe the Federal Government (i.e. NHTSA) regulates equipment used on such vehicles….at least I’ve never seen such regulations if they exist.

Bottom line…the difference between the two is the light transmittance or clarity. AS 1 or 2 would not have any effect on whether the glass broke or not.

Q: I'm trying to determine if there is an existing standard for weathering of common window glass, color-shift in sunlight, etc. Can you help?

A: All standards related to glass are found in the ASTM 2009 version of Annual Book of Standards, Section 15, Volume 15.02, Glass and Ceramic Whitewares. The book may be purchased at

Q: I installed 8 sections of frameless glass railings, each section about 2 ft high and 7 ft long. I can see a small imperfection, a small thin line, across the top of the railing. My supplier says this is normal with tempered glass and that is not an imperfection. The client says he wants the railing to be taken out and replaced to avoid any future problems. And get this – the only way anyone can see the thin line is while they are wearing polarized sunglasses; no one can see this with the naked eye. Is this thin line normal or do you think it’s an indication of a problem?

A: The "line" in question is normal in this product when viewed through polarized lenses. Sometimes it even appears as a "wavy" line when the tempering oven was a little too hot. For your information, a line, or distortion, is also seen when the railing glass is laminated and viewed at an acute angle OR through polarized lenses. Other tempering effects when viewed through polarized lenses are: halos in the glass, dark and lite spots and, sometimes, a slight curvature. The temperature of the tempering oven and the viewing conditions are the key to this mystery.

Q: I notice the term “tonnes” is used offered in describing the size of a glass plant opening or the amount of glass produced in a year, but I do not know how to quantify what this means, can you help? For example, a “700 mn tonnes plant opening” means they will produce 700 million tones of glass a year, but can one draw a conclusion on the size of the glass from statements like this?

A: A "tonne" is a metric ton. Some Glass manufacturing facilities use this term to define their output. It has nothing to do with the size of the glass. Here’s more information.

Q: I am providing glass for fire rated doors and fire rated frames in a school in Pennsylvania. Does the glass have to be wired glass or can it just be safety glass?

A: Wire glass is permitted in locations that need a fire rating. However, if the location is also a hazardous location, safety glass must be used and wire glass is not an approved safety glass. Tempered glass, which is an approved safety glass, is not an approved fire rated glass (when it breaks it shatters into small "dice like" pieces, evacuates the opening, and the fire gets in).

Most fire rated glass used in schools today has a 20 minute to 1 hour rating. This means it must retain the fire for 20 minutes or 1 hour before it fails. There are several manufacturers who provide a product that will satisfy both the fire and safety codes.

I would direct you to Section 715, Opening Protectives, of the 2006 International Building Code ( or whatever year version of the code that is used in his area ). This section gives the guidelines for his problem.

Q: I had two large windows (about 8 ft tall and 5 ft wide) installed in my living room and tempered glass was not used as I requested. The company that completed the installation wants to come back and put a film over them instead of replacing them. Is it possible to place a film over a large piece of glass to make it “tempered?”

A: NO, NO, NO, & NO! That will not make it "tempered". Annealed glass is tempered in a tempering oven. This makes it "Safety Glass" and suitable for the hazardous locations that are referenced in the building codes. Applying a film over annealed glass does NOT make it Safety Glass.

If the window is 5'x 8' (the width is always stated first) and subject to human impact as defined in the building codes, then it must be Safety Glass. There are two kinds. Tempered and Laminated. Tempered is produced as I stated above. Laminated glass is made by putting a film layer BETWEEN two pieces of glass and then putting it in a laminating chamber under pressure and high temperature.

Q: This may sound like an unusual request, but here it is, my boss recalls hearing about an unbreakable glass. I'm an architect in the design group at the Massachusetts Bay Transportation Authority (Boston's bus, subway and commuter rail agency) and we are having vandalism problems with our glass windscreens and passenger shelters and would like to find a glass that can stand up to abuse. If you can point me in the right direction I would be eternally grateful.

A: There are several kinds of unbreakable glass that was developed in Europe. It is very expensive and will not stop vandals from trying to "etch" or break it. If you google "unbreakable glass" you will probably find a lot of references.

The Mass Bay Transit Authority is not alone in trying to fix the vandalism problem. There are many toughened glass products and several polycarbonate products that won't break, but they can still be defaced. Tough problem...with no real answer...yet.