Concrete
Glass replacement and glazing repair field guide for commercial work
Replacing glass means putting back the right glass: match or upgrade to the code-required safety glazing, measure and order the insulated or safety unit to size, and re-glaze it on blocks with the weeps open.
Direct answer
Glass replacement looks like swapping a pane, but the part that matters is putting back the right glass. Code requires safety glazing, tempered or laminated, in hazardous locations like doors, sidelites, low glass, and wet areas. Match or upgrade to it, order the safety glass or insulated unit to size, and never field-cut tempered.
Key takeaways
- Match or upgrade to the code-required safety glazing; never put plain annealed glass in a hazardous location, which is illegal and dangerous.
- The location, not the broken piece, sets the requirement: doors, sidelites, low glass, and wet areas require tempered or laminated per IBC Section 2406.
- Tempered glass and insulated units cannot be field-cut; measure tip-to-tip (daylight plus bite each side) and order to finished size.
- A fogged double-pane window is a failed edge seal; replace the whole sealed unit matched to makeup and coating, since there is no lasting field repair.
- Set glass on setting blocks at the quarter points, never the corners, and keep weep holes open so the IGU edge does not sit in water.
What glass replacement really is
Glass replacement is identifying the broken or failed glass and the location it sits in, then putting back glass that meets or beats what the code requires there. The pane that comes out tells you part of the story. The location tells you the rest, because the building code requires safety glazing in specific hazardous spots whether the old glass had it or not.
That is the whole job in one sentence: match the glass to the code, not to the piece you are pulling out. A broken lite in a door, beside a door, near the floor, or next to a tub has to come back as safety glazing. A fogged insulated unit comes back as a sealed unit of the same makeup, with the same coating and performance, ordered to size. Re-glaze it with the right method and the right seal and you are done.
This guide is about replacement and repair, which is a different animal from putting up a new wall. The new storefront, curtain wall, and glazing system is its own work, covered in the curtain wall and glazing installation guide. The building envelope and energy side, the air sealing and the U-factor, lives in the envelope guide. This one is the broken pane, the failed unit, and the call you make at the opening.
The first rule: put back the right glass
Match or upgrade to the code-required safety glazing every time. This is the rule that the rest of the job hangs on, and it is the one that gets broken most. A glazier who pulls a broken tempered lite out of a door and sets plain annealed glass back in has done something both illegal and dangerous, and the fact that the glass fits the frame does not change either word.
Annealed glass breaks into long knife-edged shards. Tempered breaks into small blunt pebbles. Laminated holds together on its interlayer. In a hazardous location the code wants the failure to be survivable, which means tempered or laminated, not annealed. When you cannot tell what the old glass was, you treat the location as the authority: if it is a code-defined hazardous location, the replacement is safety glazing, full stop.
Upgrade is always allowed, downgrade never. You can put laminated where tempered would have done, or a thicker unit where the spec allows, but you cannot drop from safety glazing to annealed. Which exact category and standard the location demands comes from the adopted building code, CPSC 16 CFR 1201, and ANSI Z97.1, and the AHJ has the final read on the location. Confirm the requirement against the adopted edition before you order, because guessing here is the most expensive guess on the job.
Where does the code require safety glazing?
Safety glazing is required wherever normal use of the building makes human contact with the glass likely. The International Building Code spells these out as hazardous locations in Section 2406, and the glazing has to pass the impact test in CPSC 16 CFR 1201 or ANSI Z97.1 for that location. The list below is the common version, but the exact dimensions shift between code cycles and amendments, so confirm the adopted edition and the AHJ before you commit.
Glazing in any door, swinging, sliding, or folding, is the broadest rule and carries no size or height exception. Sidelites and glazing next to a door are caught when the glass is within a set arc of the door edge and its bottom edge is low enough to walk into. Large panes near the floor, glazing in and around wet areas like tubs, showers, saunas, and pools, and glazing along stairs, landings, and ramps round out the list. The thresholds for pane size, edge height, and distance are the part that changes, so read them off the adopted code, not from memory.
The practical takeaway for replacement work is that the location decides, not the broken piece. If the opening is a code hazardous location, the replacement is tempered or laminated that meets the required impact category, even if somebody put annealed in there years ago and got away with it.
| Hazardous location (common) | What the code generally wants | Field note |
|---|---|---|
| Glass in a door | Safety glazing, no exception | Every door lite, any size |
| Sidelite or glass beside a door | Safety glazing within the arc, low edge | Confirm arc and edge height to adopted code |
| Large pane near the floor | Safety glazing | Size, edge height, and reach thresholds apply |
| Wet area (tub, shower, pool, sauna) | Safety glazing below set height | Confirm height above standing surface |
| Along stairs, landings, ramps | Safety glazing | Confirm distance and edge height |
Annealed, tempered, and laminated
Three glass types cover almost everything you replace, and they fail in three different ways. Annealed is ordinary float glass, cut to size and not heat-treated. It breaks into large sharp shards, which is why it is barred from hazardous locations. Tempered is heat-treated to roughly four times the strength of annealed and breaks into small blunt fragments, which is what makes it safety glass. Laminated is two lites bonded over a plastic interlayer, usually PVB, that holds the broken glass in place instead of letting it fall.
For replacement, the type you put back is driven by the location and the spec, not by what is cheapest on the rack. A storefront door gets tempered or laminated. A security or sound application gets laminated. A standard upper-floor vision lite that is not a hazardous location can be annealed, often inside an insulated unit. When the original was a safety type and the location calls for it, you match the safety type and the impact category, and you verify the call against the adopted code and the AHJ rather than the brochure.
| Type | How it breaks | Where it goes |
|---|---|---|
| Annealed (float) | Large sharp shards | Non-hazardous vision glass, often inside an IGU |
| Tempered (heat-treated) | Small blunt pebbles | Doors, sidelites, low glass, wet areas |
| Laminated (PVB interlayer) | Holds together on the interlayer | Security, sound, hurricane, overhead, safety |
| Heat-strengthened | Larger fragments, not a safety glass alone | Spandrel and thermal-stress use, not for hazardous locations |
Tempered glass: order to size, read the bug
Tempered glass cannot be cut, drilled, ground, or notched after it is made. The whole point of tempering is the locked-in stress, surface compression over a tense core, and the moment you break that balance with a wheel or a bit, the lite explodes into pebbles on the bench. So you measure, you order to the finished size, and you wait for it. There is no trimming a tempered lite to fit on site.
You identify tempered glass by the permanent mark, the bug, etched in a corner. It reads something like tempered, safety glass, or the standard it meets, often with the fabricator name and ANSI Z97.1 or 16 CFR 1201. No bug does not prove annealed, since some older or specialty units were marked differently, but a visible bug is solid confirmation that the location was glazed as safety glass and the replacement must be too.
Tempered carries one quirk worth knowing: spontaneous breakage from a nickel sulfide inclusion. A microscopic NiS stone, left in the glass from manufacturing, slowly changes phase and expands years later, and in the core tension of a tempered lite that is enough to let go with no impact at all. It is rare, on the order of one stone per several tons of glass, but it is why a tempered lite sometimes shatters on a calm day with nobody near it. Where that failure is unacceptable, the spec moves to laminated or heat-soaked glass, which is a decision for the manufacturer and the designer.
Laminated glass: the interlayer that holds together
Laminated glass is two or more lites bonded over a plastic interlayer, most often polyvinyl butyral, PVB, sometimes a stiffer ionomer like SentryGlas for structural and hurricane work. When it breaks, the fragments stay stuck to the interlayer instead of falling out, so the opening stays closed and the glass stays put. That single property is what makes laminated the glass of choice for security, forced-entry resistance, overhead glazing, and anywhere a fall-through is the hazard.
It does three jobs at once. It is a safety glazing when the interlayer is thick enough to pass the impact standard, a common threshold being a 0.030 in or thicker PVB to meet ANSI Z97.1. It is a security and hurricane glass because the interlayer resists penetration and holds the lite in the frame after impact. And it cuts sound, since the interlayer damps vibration and an asymmetric laminated makeup raises the STC noticeably over plain glass.
Laminated can be cut to size as annealed laminated, but the cut is a glass-and-interlayer operation, not a quick score-and-snap, and tempered laminated cannot be cut at all. For replacement, match the interlayer type and thickness to the original and the spec, because a thinner or different interlayer can drop the security, acoustic, or impact rating the building was designed around. Confirm the makeup against the manufacturer and the project documents.
The insulated glass unit, and why it is the common job
An insulated glass unit, the IGU, is two or more lites separated by a spacer around the perimeter, sealed at the edge, with a dead air or gas fill in the cavity. The spacer holds a desiccant that dries the cavity at the factory, and the edge seal keeps it dry and sealed for the life of the unit. The fogged double-pane window everyone calls about is a failed IGU, and replacing it is the most common glass job on a commercial building.
The key fact for repair: you replace the whole sealed unit, not one pane. The lites, the spacer, the desiccant, the gas fill, and the seal are a single manufactured assembly. You cannot open it, wipe the inside, and reseal it in the field and have it last. When the seal goes, the unit is done, and the fix is a new unit of the same overall thickness, the same lite makeup, and the same coating, ordered to size.
Which lite carries the safety glazing matters here too. In a hazardous location the unit has to contain tempered or laminated glass that meets the impact category, often both lites or the lite on the contact side, per the adopted code. So an IGU replacement in a door or sidelite is not just any sealed unit, it is a sealed unit built with the right safety glass. Spell that out on the order.
Why is my double-pane window foggy?
A double-pane window fogs because the edge seal has failed and the unit can no longer keep its cavity dry. Moisture works past the failed seal, the desiccant in the spacer absorbs it until it is saturated, and after that the water vapor condenses on the inside faces of the glass as haze, droplets, or a film you cannot wipe off because it is sealed between the panes.
The seal fails from the things that work on every sealed joint over time: ultraviolet breaking down the sealant, daily thermal cycling flexing the edge, water standing against the edge in a glazing pocket that does not drain, and plain age. A conventional aluminum spacer makes it worse by conducting heat straight across the edge, which drives more condensation and stress there; warm-edge spacers and dual seals last longer for the same reason. Typical service life runs in the 15 to 25 year range depending on climate, exposure, and how the unit was glazed.
There is no field repair worth doing. The defog gimmicks that drill the unit and vent it do not restore the seal, the gas fill, or the dried cavity, and the haze comes back. The honest answer to a fogged unit is a new sealed unit. Measure it, match the makeup and the coating, and order it to size.
How do you measure for a replacement unit?
You measure the daylight opening, then add the bite on each side to get the tip-to-tip size of the glass. The daylight opening, the DLO, is the visible glass you see between the stops. The bite is how far the frame or stop laps over the glass edge and holds it. Tip-to-tip, the actual ordered size, is the daylight width plus twice the bite, and the daylight height plus twice the bite, less a small edge clearance so the lite drops into the pocket.
Measure the existing glass tip-to-tip directly when you can pull a stop and reach the edge, because that is the number the shop builds to. Measure in three places across width and height and take the smallest, since frames rack and openings are rarely square. Get the overall thickness too: a single lite thickness, or the full IGU thickness across both lites and the spacer, because the new unit has to land in the same glazing pocket and under the same stop.
The reason measuring carries so much weight is that you cannot fix a mistake with a saw. Tempered cannot be cut, and an IGU cannot be cut at all without destroying the seal. Both are made to the finished size and shipped that size. Order it wrong and you eat the lead time twice. Account for the lead time up front, since safety glass and insulated units are built to order and rarely sit on a shelf.
Ordering the right unit
The order is more than a size. A glass order that holds up names the finished size tip-to-tip, the glass type and the safety category for the location, the overall thickness and the lite makeup, the coating, the spacer, and the fill. Miss any one and the unit either does not fit the pocket, does not meet the code, or does not match the building it sits in.
Coating is the line that gets skipped most. A low-E coating sits on a specific surface inside the unit, and there are several low-E products with different solar and U-factor numbers. Order a clear unit to replace a low-E unit and the new lite will look slightly different from its neighbors and perform worse, which a facility manager notices the first sunny afternoon. Match the coating and the surface to the original, and match the spacer type and gas fill while you are at it.
Spell out the safety glazing on the order in writing, by category. If the location is a hazardous one, the order says tempered or laminated meeting the required impact category, not just insulated unit. Build in the lead time, since tempered, laminated, and insulated units are made to order. For a special makeup, a heavy laminated, a hurricane unit, an odd coating, the lead time stretches further, so order early and confirm the build against the manufacturer and the spec.
Wet glazing, dry glazing, and the bite
Re-glazing the new lite happens one of two ways, wet or dry, and the frame usually dictates which. Wet glazing beds the glass with a tape, mastic, or gunnable sealant between the glass and the frame and stop. Dry glazing holds the glass with compression gaskets, often a wedge gasket snapped against a fixed stop. Many systems are a hybrid, a dry gasket on one face and a wet seal or tape on the other.
Wet glazing, done right, is the better air and water seal, but it is slower and it has to be tooled and cured. Dry glazing goes faster and is cleaner to service, since you pull a stop and a gasket instead of cutting cured sealant, but the gasket has to be the right size and fully seated or it leaks and whistles. Match the method and the materials the system was built for, because mixing an incompatible sealant against a gasket can attack the gasket or the IGU edge seal.
The bite is what actually holds the glass and seals it. Too little bite and the lite can work loose or leak under wind and pressure. Too much bite shades more of the glass edge and can build thermal stress there, which matters on tinted, reflective, and heat-absorbing glass. Center the glass in the opening so the bite is even all the way around, and confirm the nominal bite against the system and the glass manufacturer.
| Method | How it seals | Trade note |
|---|---|---|
| Wet (tape, mastic, sealant) | Bedded and tooled against frame and stop | Best air and water seal, slower, must cure |
| Dry (compression gasket) | Wedge or gasket snapped against the stop | Fast and serviceable, gasket must be fully seated |
| Hybrid | Dry gasket one face, wet seal the other | Common in storefront and window systems |
| Structural silicone | Glass bonded to the frame with silicone | Specialty, follow the silicone manufacturer |
Setting blocks carry the weight, not the corners
Setting blocks are the small load-bearing pads the glass sits on in the bottom of the glazing pocket, and they carry the full weight of the lite. The rule the trade follows is two blocks per lite at the quarter points of the width, no closer in than the eighth points, never at the corners. Set the glass on the corners and you concentrate the whole weight on two edges that are already the weakest part of the lite, and you crack it, sometimes weeks later.
The blocks are sized to the job. They support the full thickness of the glass or the full IGU, they run about 1/16 in narrower than the channel so they do not pinch, and a common length rule is roughly 0.1 in of block per square foot of glass, with a 4 in minimum. They are usually 80 to 90 durometer EPDM, neoprene, or silicone, hard enough to hold the load without crushing. Silicone blocks belong with silicone sealant, since the chemistry has to be compatible.
Block height matters as much as position. The blocks hold the glass up off the bottom of the pocket so the edge keeps its clearance and, just as important, so the IGU edge does not sit down in the water that collects in the pocket. A block that is too short, or a glazier who skips the blocks and lets the lite bottom out, puts the sealed edge in standing water and starts the seal failure all over again.
Structural silicone glazed glass (SSG)
Some glass is held in the frame by a structural silicone bond rather than a captured stop, which is the SSG system you see on flush, gasket-free facades. The silicone carries the wind load from the glass back to the frame, so replacing an SSG lite is a different and more demanding operation than swapping a captured lite. It is specialty work, and the field bond has to be built and cured to the silicone manufacturer's procedure, not improvised.
On most SSG replacements the broken lite and its old silicone beads are cut out, the surfaces are cleaned and prepped to the letter, and the new lite is set and bonded, often from the interior, with new structural beads. Field bonding is held to a tighter standard than shop bonding because the jobsite is dirty and the cure conditions are not controlled. Surface prep, primer, joint dimension, and cure time all follow the sealant manufacturer's written guideline, and the new bond needs full cure before it carries load.
This is where replacement and new installation meet, and the curtain wall and glazing installation guide covers the SSG system and its mock-up and testing in depth. For a repair, the short version is that an SSG lite is not a captured lite, the silicone is structural, and the manufacturer's procedure and the project documents govern the whole operation. If the bond is in doubt, you do not glaze it.
The frame, the stop, the channel, and the weep
The glass is only as good as the pocket it sits in, so prep the frame before the new lite goes anywhere near it. The glazing channel has to be clean, sound, and dry, with the old sealant, broken gasket, and glass shards fully cut out. Leftover cured sealant under a new bed seal keeps the new seal from wetting the frame, and a tired gasket that gets reused leaks within a season.
Check the channel and the stop for condition while it is open. A bent stop, a corroded sill, a frame that has racked out of square, or a glazing pocket packed with old debris all change how the new lite seats and seals. Replace the gaskets rather than fighting old ones back in, since gaskets take a compression set and never seal the same twice. Confirm the gasket profile and the stop are the ones the system used.
Find the weep holes before you set glass, because they decide whether the pocket drains. A drained glazing pocket has weep openings at the sill that let any water that gets past the face seal run back out. They have to be open and clear when you finish. Plugging them with sealant during the re-glaze, which is an easy reflex, traps water against the new IGU edge and sets up the next seal failure.
Removing the broken or old glass
Removal is where most of the cuts happen, so treat the broken lite as the hazard it is. For a captured lite, pull the stops first, the removable side, and free the gasket or cut the sealant bead along the bedded face. A broken IGU often comes out in pieces, and the edge seal and spacer can hold jagged glass under tension, so glove and sleeve up and clear the loose shards before you reach in.
Cured sealant is cut, not pried. A glazing knife or an oscillating tool with a flush blade parts the bead cleanly; prying a stop against a stuck bead bends the stop and scatters glass. On an SSG lite the structural bead is cut deliberately to release the lite, which is a controlled operation, not a yank. Keep suction cups on intact glass for control as you free it, and never trust a cracked lite to stay in one piece while you handle it.
Plan the disposal before the glass is out. Broken glass goes in a dedicated rigid container or a glass cart, not a trash bag that a shard will tear through and a shoulder will catch. Sweep and vacuum the pocket and the floor under it, because the small fragments are the ones that find a hand or a knee later. A clean pocket is also the start of a clean re-glaze.
How do you handle glass safely?
Glass cuts and glass weight are the two injuries on this work, and both are predictable. A square foot of 1/4 in glass runs around 3 lb, so a storefront lite or a large IGU gets into the hundreds of pounds fast, well past a one-person lift. The rule is simple: if it is big or heavy, it is a two-person carry or a lift, with suction cups for grip and control, not a hero lift that ends with a dropped lite and a trip to the ER.
Cut protection is gloves and sleeves rated for glass, closed footwear, and eye protection, every time, including during cleanup. The cuts that send people for stitches usually happen on a broken lite during removal or while clearing shards, not during the set. Suction cups are for handling and positioning intact glass and give you a controlled grip; they are not a sling and they are not for lifting a cracked lite, which can let go under the pull.
The fall is the other danger, and it shows up on storefront and ladder work and on anything above the ground floor. Glass and ladders are a bad mix, since a slip with a lite in your hands takes both of you down. Use the right access, scaffold or a lift instead of a ladder for a heavy lite, keep both hands and your balance on the access and let the cups and a second person carry the glass. Where a fall hazard exists, the OSHA fall-protection rules and the site safety plan govern.
Emergency board-up and temporary closure
When a storefront or a vision lite breaks and the replacement glass is days out on a lead time, the opening gets secured the same day with a temporary closure. A board-up keeps the building dry, secure, and safe to walk past until the right glass arrives, and it is a separate scope from the glazing itself. The board-up and emergency closure work is covered in its own cross-linked guide; this is the handoff point between the two.
The common temporary closures are plywood or OSB screwed or clipped into the opening for security, or clear polycarbonate sheet when the storefront has to keep working and stay visible while the glass is on order. Polycarbonate buys daylight and a storefront that still looks open; plywood buys security on a smashed entry overnight. Either way it is temporary, and it is sized and fastened so it does not damage the frame the permanent glass has to go back into.
The reason to separate the two in your head is sequence and money. The board-up is the emergency call. The glass replacement is the scheduled return when the unit shows up. Measure for the real glass while you are there for the board-up, so the lead time starts the same day the break does and the opening is only boarded once.
Setting the new glass
With the pocket clean and the unit on site, the set goes in order. Place the setting blocks at the quarter points first, level and at the right height. Lower the lite onto the blocks with suction cups and a second set of hands, then center it in the opening so the bite and the edge clearance are even on all four sides. A lite shoved hard to one side robs bite on the far side and overbites the near side, which is where leaks and edge stress start.
Seal it by the method the frame was built for. Wet systems get the tape or sealant bedded and the stops set to compress it, then the perimeter is tooled and left to cure. Dry systems get the wedge or compression gasket seated fully into the channel, with no gaps at the corners where a short gasket pulls back. Set the removable stops last, and on a face-sealed perimeter, cap and tool the sealant in a continuous bead with no skips.
Then check your work while it is fresh. The glass centered, the bite even, the blocks carrying the weight, the gaskets seated, the cap bead continuous, and the weeps open and clear. Clean the glass and the frame before the sealant skins over and the dust sets into it. A re-glaze that looks clean and drains is a re-glaze that lasts; one with a plugged weep or a starved corner is a callback waiting for the first hard rain.
Keep the weeps open: the IGU edge cannot sit in water
The single detail that quietly kills insulated units in a frame is a drowned edge. The glazing pocket is meant to drain, with weep holes at the sill that carry any water that gets past the face seal back out to the exterior. Leave those weeps open and the pocket stays dry; plug them and water pools in the pocket and stands against the bottom edge of the glass.
An IGU edge sitting in standing water is a seal failure on a timer. The edge seal is the one part of the unit that cannot live wet, and constant immersion breaks it down and pulls moisture into the cavity, which is the same fogging the unit was replaced to cure. This is why the setting blocks hold the edge up out of the pocket and why the weeps have to stay clear. The two details work together.
During a re-glaze the weeps get plugged by accident more often than not, smeared shut with the same sealant that caps the perimeter. Find them, keep them open, and check that they actually pass water before you leave. The drained glazing pocket is the same principle the curtain wall and storefront systems are built on, covered in the curtain wall and glazing installation guide; on a repair you are just not allowed to break it. Confirm the drainage detail against the system manufacturer.
Match the low-E coating and the unit performance
A replacement insulated unit has to match more than the size. The original unit was specified for a U-factor, a solar heat gain coefficient, and a visible light level, and most of that comes from the low-E coating and the gas fill. Drop in a clear unit where a low-E unit was and the replacement looks different against its neighbors and lets in more heat and more glare, which the people in the space feel and the energy bill shows.
Match the coating type and the surface it sits on, the spacer, and the gas fill to the original, or to the current spec if the building is being upgraded. There are several low-E products with different numbers, so clear versus low-E is not enough detail on an order; the specific coating and surface are what keep the new lite matching the wall it sits in. When in doubt, identify the existing coating and order to it.
The energy and comfort side of the glass, the U-factor, the air sealing around the opening, and how the window fits the whole building envelope, is its own subject, covered in the building insulation and air sealing envelope guide. For a replacement, the job is to put back the performance that was there, or better, and to confirm the unit makeup against the manufacturer and the project documents.
The IGU warranty and the documentation
Insulated units carry a seal warranty, and it is only as good as the paper behind it. The warranty covers seal failure, the fogging, for a stated term, but it usually depends on the unit being glazed the way the manufacturer requires: a drained pocket, the edge held up out of water, a compatible sealant against the edge seal, and proper setting blocks. Glaze it wrong and the manufacturer can decline the claim, and they will look at exactly those details.
Compatibility is the trap. The sealant or tape that touches the IGU edge has to be compatible with the edge seal, or it attacks the seal and you have caused the failure you are warranting against. This matters most with silicones and certain tapes, so confirm the glazing materials against the IGU manufacturer before they go in the pocket. Keep the unit's date stamp and the order paperwork, since both the warranty term and the spec are read off them.
Document the install so the warranty is defensible. Record what unit went in, the makeup and coating, the date, the glazing method and materials, and that the weeps were left open and the blocks set right. The next person to open that frame, or the manufacturer reviewing a claim, reads the record, not your memory.
What to record
The record on a glass job answers one question down the road: was the right glass put back the right way? For a hazardous location that question can come from an inspector or an insurer, and the answer lives in what you wrote down at the opening. Capture the glass type and safety category, the location and whether it is a code hazardous location, the finished size, the makeup and coating, the glazing method and materials, and that the weeps were left open.
This is field-tool work, not a clipboard that gets lost. Logging the location, the unit makeup, the safety category, and a photo of the bug and the finished set in FieldOS ties the glass that went in to the opening it went in, with a date and a name on it. When a fogged unit returns under warranty or an inspector asks why a door lite is what it is, the record is right there instead of in somebody's head.
| Item to record | Requirement | Note |
|---|---|---|
| Location and hazard status | Identify code hazardous locations | Drives the safety glazing call |
| Glass type and safety category | Match or upgrade to code | Tempered or laminated, per CPSC 16 CFR 1201 or ANSI Z97.1 |
| Finished size (tip-to-tip) | Ordered to size, no field cut | Daylight plus bite each side |
| IGU makeup and coating | Match original or current spec | Low-E surface, spacer, gas fill |
| Glazing method and materials | Match the system, IGU-compatible | Wet, dry, or structural silicone |
| Weeps and setting blocks | Weeps open, blocks at quarter points | Edge held out of water |
Common mistakes
- Replacing safety glass with plain annealed in a hazardous location, which is both illegal and dangerous.
- Trying to field-cut tempered glass or an insulated unit, which destroys the lite or the seal.
- Setting the glass with no setting blocks, or blocks at the corners, so the lite bears wrong and cracks.
- Plugging the weep holes during the re-glaze so the IGU edge sits in standing water and the seal fails.
- Ordering the wrong size, the wrong thickness, or a clear unit where a low-E unit belonged.
- Using a sealant or tape against the IGU edge that is not compatible with the edge seal.
- Handling a heavy or broken lite alone, or lifting cracked glass on suction cups.
Field checklist
Want this checklist to run itself on every job — with photo proof and a signed record crews can hand the customer? That's FieldOS.
Standards and references
The safety-glazing framework lives in the building code and the impact standards it points to. The International Building Code, Section 2406, defines the hazardous locations where safety glazing is required, and it sends the glazing to the impact tests in CPSC 16 CFR 1201, the federal safety standard, with Category I and Category II covering smaller and larger glazing areas. ANSI Z97.1 is the consensus impact standard the industry also marks to. The exact locations, thresholds, and which standard applies vary by adopted edition and amendment, so confirm them against the code the jurisdiction actually adopted and the AHJ.
The glass and the insulated unit themselves answer to the fabricator and to IGMA, the Insulating Glass Manufacturers Alliance, for unit makeup, durability, and the seal warranty. The glazing details, the bite, the setting blocks, the compatible sealants, and the drained pocket, come from the glass and system manufacturers' glazing guidelines, and they are the authority on what their unit needs to stay sealed and warranted.
Cite the standard that controls the point. The code and CPSC 16 CFR 1201 govern whether the location needs safety glazing and which category. The glass and IGU manufacturer govern the makeup, the compatible materials, and the warranty. The AHJ has the final read on the installation. The three rules that carry the job: match or upgrade to the code-required safety glazing, order the right insulated unit or safety glass to size with no field cut, and set it on blocks with the weeps open and the glass handled safely.
Units and terms
Glass replacement carries its own vocabulary, and the same opening can read differently across a spec, a glass order, and a manufacturer sheet. The terms below are the ones that change the order or the install when they are misread.
Size is given tip-to-tip, the finished glass dimension, derived from the daylight opening plus the bite on each side. Glass thickness runs in inches or millimeters; insulated unit thickness is the overall across both lites and the spacer. Impact category comes from CPSC 16 CFR 1201 as Category I or II, and from ANSI Z97.1 as a class. Match those to the location every time.
- Glass replacement / re-glazing
- Removing failed or broken glass and setting new glass that meets or beats the code-required glazing for the location
- Annealed / tempered / laminated
- Ordinary float glass that breaks in shards, heat-treated glass that breaks in pebbles, and bonded glass that holds together on an interlayer
- Safety glazing / hazardous location
- Tempered or laminated glass meeting an impact standard, required by code in locations like doors, sidelites, low glass, and wet areas
- IGU / seal failure / fogging
- Insulated glass unit, two or more lites sealed around a spacer; when the edge seal fails the cavity fogs and the unit is replaced whole
- Setting blocks
- Load-bearing pads under the glass at the quarter points that carry the weight and hold the edge up out of the drainage pocket
- Daylight opening / bite
- The visible glass between the stops, and the amount the frame or stop laps over and holds the glass edge
- Wet vs dry glazing
- Sealing the glass with tape or sealant against the frame, versus holding it with compression gaskets
- Weep / drained glazing pocket
- Sill openings that drain water out of the glazing pocket so the IGU edge does not sit in standing water
FAQ
Why is my double-pane window foggy?
A foggy double-pane window has a failed edge seal. Moisture works past the seal, the desiccant in the spacer saturates, and water vapor then condenses between the panes as a haze you cannot wipe off. The seal fails from UV, thermal cycling, age, and a glazing pocket that does not drain. The fix is a new sealed unit.
What is safety glazing?
Safety glazing is glass that breaks safely, either tempered, which crumbles into blunt pebbles, or laminated, which holds together on its interlayer. Code requires it in hazardous locations like doors, sidelites, low glass, and wet areas, where the glass passes the impact test in CPSC 16 CFR 1201 or ANSI Z97.1. Confirm against the adopted code.
Can you replace tempered glass with regular glass?
No. Replacing tempered safety glass with plain annealed glass in a code hazardous location is illegal and dangerous, because annealed breaks into knife-edged shards. The location, not the broken piece, sets the requirement, so a door or sidelite lite has to come back as tempered or laminated meeting the required impact category. You can upgrade, never downgrade.
What is an IGU?
An IGU, an insulated glass unit, is two or more glass lites separated by a perimeter spacer, sealed at the edge, with a dry air or gas fill in the cavity. The spacer holds a desiccant that keeps the cavity dry. It is a single sealed assembly, so when the seal fails you replace the whole unit, not one pane.
How do I know if glass is tempered?
Look for the permanent etched mark, the bug, in a corner. It usually reads tempered or safety glass with the fabricator and a standard like ANSI Z97.1 or 16 CFR 1201. No bug does not prove annealed, but a visible bug confirms the location was glazed as safety glass, so the replacement must be a safety type too.
Can a fogged insulated glass unit be repaired?
Not in any lasting way. Once the edge seal fails, the cavity, the desiccant, and the gas fill are compromised, and the defog tricks that drill and vent the unit do not restore the seal, so the haze returns. The honest fix is a new sealed unit, matched to the original makeup and coating and ordered to size.
Tempered or laminated: which should I use?
Both are safety glass. Tempered breaks into blunt pebbles and is the common choice for doors and sidelites. Laminated holds together on its interlayer, which adds security, sound control, and impact resistance, and it stays in the opening after breaking. Match what the original was and what the spec calls for, and confirm the location against the adopted code.
How long does it take to get replacement glass?
Tempered, laminated, and insulated units are built to order, so plan on a lead time rather than same-day glass. A standard unit can run days to a couple of weeks; a special coating, a heavy laminated, or a hurricane unit runs longer. Measure and order the day of the break, and board up the opening while it is on order.
Do I need safety glass next to my door?
Often yes. Glass in a sidelite or panel beside a door is a code hazardous location when it falls within a set arc of the door edge and its bottom edge is low enough to walk into. The exact arc and height thresholds vary by adopted edition, so confirm against the building code and the AHJ.
What do I do when a storefront glass breaks after hours?
Secure the opening first with a temporary closure, plywood for security or clear polycarbonate to keep the storefront usable, fastened so it does not damage the frame. Measure for the real glass the same visit so the lead time starts immediately. The board-up is the emergency scope; the glass replacement is the scheduled return when the unit arrives.
People also ask
Codes cited in this guide
This guide is written and reviewed against the published standards below. Always confirm the current adopted edition with the authority having jurisdiction.