The working reference on polycarbonate skylights for commercial roofing contractors, industrial facility managers, architects and specifiers, and agricultural and greenhouse builders. What the material does that glass and acrylic cannot, which unit types fit which roofs, and how to compare the specs before you buy.
The material
A polycarbonate skylight is a roof glazing unit whose light-transmitting surface is made from polycarbonate, an engineering thermoplastic that took over commercial daylighting for one blunt reason: overhead glazing gets hit. Hail, dropped tools, wind-blown debris and foot traffic near the curb all land on the weakest plane of the building, and polycarbonate absorbs what breaks everything else.
Against glass, the comparison is not close. Polycarbonate is commonly rated at around 200 times the impact resistance of glass at the same thickness, at less than half the weight, which means lighter framing, simpler lifting and far less risk during installation. Against acrylic, the other common skylight plastic, polycarbonate gives up a little optical clarity and gains an enormous margin of toughness plus better behavior in fire tests.
Two engineered features finish the case. A co-extruded UV cap layer on the weather face protects the sheet from the sun that yellowed early-generation plastic glazing, and diffusing grades scatter incoming light so a bay is lit evenly edge to edge instead of striped with glare and hot spots.
vs glass
A fraction of the weight, a multiple of the impact strength, and no shattering hazard over occupied space.
vs acrylic
Many times tougher against hail and vandalism, with a wider service temperature range.
vs metal panel
The one roof material that pays rent: free light, every daytime hour, for the life of the sheet.
Diffused daylight from roof glazing lights a high-bay space evenly, without the glare stripes that clear glazing casts on the floor.
Configurations
The same material shows up in very different products. What separates them is the shape of the opening, how the unit meets the roof, and whether it has a job beyond daylight, such as venting smoke in a fire.
Daylight along the spine of the building
The workhorse curb unit
Geometry as a design feature
Long-span curved glazing
Glazing that behaves like roofing
Skylights with a life-safety job
Reading the data sheet
Skylight submittals bury the decision in figures. A handful of them determine whether the unit lights the space, holds heat, satisfies the code official and survives the weather. Here is what each one is telling you, and the trap that rides along with it.
| Specification | What it governs | What to watch for |
|---|---|---|
| Light transmission | The share of visible light that reaches the interior. Clear solid sheet passes close to 90 percent; multiwall grades range roughly from 40 to 80 percent by wall count and tint. | Higher is not automatically better. Diffusing grades transmit less on paper but light the floor more usefully, without glare patches over workstations. |
| U-value | How fast heat crosses the glazing. Multiwall sheet traps air in its channels: even twinwall beats single glazing, and thick five- and seven-wall sheets approach double-glazed performance. | Compare center-of-glazing versus whole-unit numbers. A superb sheet in an uninsulated aluminum frame loses much of its advantage at the perimeter. |
| Solar heat gain (SHGC) | How much of the sun's heat comes in with the light. Tints, opal diffusion and IR-blocking grades pull the number down for cooling climates. | In heating climates some gain is welcome. Match SHGC to the climate zone and the energy code, not to a generic 'lower is better' rule. |
| Multiwall vs solid | Solid sheet is glass-like and strongest against point impact; multiwall is lighter per area, far better insulating, and inherently diffusing in opal grades. | The wall count and thickness must match the span and load tables. A thicker sheet is not stronger if the ribs run the wrong way for the span. |
| Impact & hail rating | Documented resistance to hail and debris, from material-level impact values to unit-level severe-hail approvals used by insurers. | Ask for the tested assembly, not the resin brochure. A tough sheet in a brittle frame or with weak fastening still fails at the connection. |
| Fire classification | Light-transmitting plastics are classified by burning behavior under the building code, which drives allowable areas, separations and where units may be installed. | Confirm the classification of the actual sheet being supplied. Area limits as a fraction of the roof differ by class, and the code official will check. |
| Condensation control | How the unit manages the moisture a warm humid interior pushes at cold glazing: thermal breaks, condensation gutters, vented and taped flute ends. | Over pools, washdown areas and greenhouses this spec matters more than U-value. Ask specifically how the unit drains what condenses. |
| Fall protection provisions | Whether the unit ships with, or accepts, a screen or security bar system, and whether the assembly is tested against a person falling onto it. | OSHA treats every skylight as a hole in the roof. Protection is a requirement of working near one, whatever the glazing material. |
Under U.S. OSHA rules a skylight is treated as a hole in a walking working surface. Anyone on the roof near one must be protected by a screen or cover rated for the load, a guardrail system, or personal fall arrest. Glazing toughness is not a substitute: even panels tested to resist a falling person are a last line of defense, not a walking surface. Write the protection method into the spec at the same time as the skylight itself, because retrofitting screens after an incident is the expensive order of operations.
Performance figures vary by manufacturer, sheet structure and assembly. Always work from the published data for the specific product being supplied rather than from generic material values.
Selection
Three questions sort the catalog quickly: what roof is the unit going into, what will the local climate throw at it, and how much glazing, where, does the daylight target actually require.
Most skylight problems are edge problems. The sheet almost never leaks; the curb, the flashing, the fastening and the movement joints do. Polycarbonate expands and contracts noticeably more than the metal around it, so the glazing details must let the sheet move: oversized fastener holes, the manufacturer's gaskets and bars, and sealants chosen for compatibility with polycarbonate.
A quote worth comparing names the unit, the curb or profile match, the flashing scope, the fall protection method and the warranty terms in the same document.
Who uses them
Curb units and panel systems are line items on reroofs and new membranes, and polycarbonate keeps them off the callback list: no shattered domes after a hail event, no crane time for heavy glass, and panel systems that flash with the same skills as the roof itself. Replacing brittle, yellowed acrylic domes at reroof time is one of the easiest upsells in the trade.
In a high-bay plant or warehouse, lighting runs all day whether the sun is out or not. Skylights covering a small share of the roof displace a large share of that load, improve color rendering on the floor, and keep working light on during daytime power interruptions. Diffusing multiwall grades do it without glare over racking, machinery and forklift routes.
Polycarbonate opens shapes that glass resists: long barrel vaults, continuous ridge runs and curved canopies with light framing, in clear, opal and tinted grades. The specification work is in the details: fire classification and allowable areas under the light-transmitting plastics provisions, energy code values by climate zone, and fall protection written into the same section as the unit.
Multiwall polycarbonate is the modern greenhouse envelope: it insulates enormously better than single glass, diffuses light so plants are lit evenly instead of scorched in stripes, and shrugs off the hail that ends a glass house. On barns and livestock buildings, in-plane ridge and eave lighting panels bring daylight to spaces that would otherwise never see it.
Growers are the most demanding daylight buyers there are: light is their crop input, heating is their biggest bill, and a glazing failure can end a season. That the commercial greenhouse industry standardized on multiwall polycarbonate is the strongest practical endorsement the material has. The same properties, high diffuse transmission, real insulation and hail survival, are exactly what a warehouse or gym roof wants.
Ownership
Polycarbonate asks for very little, but the little it asks for is specific. Most premature failures trace to the wrong cleaner, missing flute closures or sealants left past their service life.
Common questions
Uncoated polycarbonate will yellow under UV exposure, and the bad reputation the material picked up decades ago traces back to early sheet that shipped without protection. Modern skylight-grade sheet is co-extruded with a UV-absorbing cap layer on the weather side, and reputable manufacturers back it with a written warranty against yellowing and loss of light transmission, commonly ten years or more. When comparing quotes, ask specifically whether the sheet is UV-capped on the exposed face and what the warranty says about yellowing index and transmission loss, because bargain sheet without the cap layer is where the horror stories come from.
Plan on 15 to 25 years of service from quality UV-protected glazing, with climate, orientation and grade moving the number in both directions. The glazing usually outlasts the soft parts around it: gaskets, glazing tapes and perimeter sealants age faster and are the usual source of leaks long before the sheet itself fails. A skylight that gets an annual inspection and timely resealing will typically reach the far end of that range.
No. No skylight glazing is a walking surface, regardless of material. OSHA treats a skylight as a hole in the roof, and anyone working near one must be protected by a screen, a railing, a cover rated for the load, or personal fall arrest. Some panel systems are additionally tested to resist a person falling onto them, but that is a last-line safety feature, not permission to step on the unit. Every year workers are killed falling through skylights, so this is one spec question that should never be negotiated away.
Multiwall sheet is a series of open channels, and if those channels are left unsealed at the ends they breathe humid air that condenses when temperatures drop. Correct installation closes the top ends with solid aluminum tape and the bottom ends with a breathable filter tape and a vented closure profile, so moisture that gets in can drain and dry out. Persistent fogging, water lines or algae inside the flutes almost always points to missing or failed end treatment rather than a defect in the sheet.
In the United States, skylight glazing made from plastics falls under the International Building Code provisions for light-transmitting plastics, which classify materials by burning behavior, limit the glazed area as a fraction of the roof, and set curb and separation requirements. Energy codes add U-value and solar heat gain limits that vary by climate zone, and high-wind jurisdictions such as Florida require units with specific wind and impact approvals. Local amendments differ, so the authority having jurisdiction and the manufacturer's code compliance documents are the final word for a given building.
Acrylic has long been the default dome material because it is optically clearer and historically weathered well, and it remains a reasonable choice in mild climates. Polycarbonate is dramatically tougher: it resists hail, vandalism and dropped tools that would crack or shatter an acrylic dome. In hail-prone regions, over occupied spaces, or anywhere a broken dome means an emergency roof opening, the impact resistance of polycarbonate is usually worth more than the last few points of optical clarity.
Clear solid sheet transmits close to 90 percent of visible light, which is in the same range as glass. Multiwall grades trade transmission for insulation, ranging roughly from 40 to 80 percent depending on wall count, thickness and tint. For working spaces the raw percentage matters less than how the light arrives: diffusing grades spread daylight evenly across the floor, eliminating the glare patches and hot spots that clear glazing casts, which is why diffused polycarbonate is the standard choice over production floors, gyms and sales areas.
Daylighting displaces electric lighting during exactly the hours most buildings are occupied, and in high-bay spaces lighting is a large share of the power bill, so well-placed skylights covering a small fraction of the roof can meaningfully cut consumption. The offsetting cost is thermal: any skylight loses more heat than the insulated roof around it, which is why multiwall construction matters in heating climates and solar-control tints matter in cooling climates. The savings case is strongest when the glazing area is sized to the daylight target rather than maximized.
Polycarbonate is the most impact-resistant glazing in common use, and resistance to hail is the main reason it gets specified over glass and acrylic in the hail belt. Severe storms can still leave cosmetic dents or surface crazing, but the failure mode that matters, a shattered opening over an occupied space, is precisely what the material is best at preventing. For insurance and code purposes, look for units that carry a recognized severe-hail approval rather than relying on the material name alone.
Get a Quote
Send the basics and we will point you in the right direction: the roof type and covering, whether this is new construction or a retrofit, roughly how many openings or how much run, and the climate the units have to survive.
Specifying a unit
Working out whether curb units, a continuous vault or in-plane panels fit the roof and the daylight target.
Comparing quotes
Making sure glazing grade, flashing scope, fall protection and warranties are priced on the same basis.
Planning a retrofit
Matching panel profiles to existing metal roofs, or replacing aged acrylic domes at reroof time.