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UV-protected polycarbonate greenhouse panels last 10 to 20 years, with 15 a reasonable expectation in most US climates. What determines it is the co-extruded UV layer on the outward face: sheet without it, or installed upside down, yellows and embrittles in 3 to 5 years. Manufacturer warranties are the useful signal — most name a 10-year term against yellowing and loss of light transmission beyond a stated threshold. Hail, heat cycling and over-tightened fasteners are the other life-limiting factors.
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What does the warranty actually promise?
This is the most concrete information available on lifespan, because manufacturers have to define failure in measurable terms. Major polycarbonate sheet makers — Palram, whose SUNTUF and SUNLITE lines are the most widely sold in US home greenhouses, along with Polygal and similar producers — typically publish a 10-year limited warranty on multiwall sheet covering loss of light transmission beyond a specified percentage and yellowing beyond a stated index change, with hail-breakage terms on corrugated products.
Two things to take from that. First, a 10-year warranty is not a 10-year lifespan — it is the period the maker will stand behind measurable optical degradation, and panels routinely serve well beyond it. Second, warranties are almost always conditional on installation per the manufacturer's instructions, which means correct face orientation, correct fastener type and torque, adequate expansion allowance, and correct channel-end taping. Get any of those wrong and the warranty is moot regardless of what the panel does.
What shortens panel life?
| Factor | Effect | What to do |
|---|---|---|
| UV layer facing inward | Yellowing and embrittlement in 3–5 years | Mark the outward face before peeling the protective film |
| Over-tightened screws | Stress cracks radiating from fasteners within a season or two | Oversize the holes, use neoprene-washered screws, do not compress the sheet |
| No expansion allowance | Buckling and cracking | Allow about 1/8 inch per 3 feet of panel length for thermal movement |
| Hail | Dents on multiwall, cracks on thin or aged sheet | Choose thicker sheet or corrugated in hail country; check insurance coverage |
| Abrasive or solvent cleaning | Crazing, permanent haze | Mild soap and water only, soft cloth |
| Open channel ends | Algae, dust and insects inside the flutes | Breathable anti-dust tape bottom, solid tape top |
| Contact with incompatible sealants | Chemical attack and cracking | Use only sealants the sheet maker lists as compatible — many silicones are not |
How do you tell when a panel is done?
Failure is gradual and mostly optical. Watch for a yellow or amber cast compared with a newer panel, hazing or clouding that does not wash off, brittleness — an old panel cracks rather than flexes when you press it — and cracks radiating from screw holes, which is the most common structural failure. Inside the flutes of twinwall, green algae staining and trapped dirt cut light transmission and cannot be cleaned out.
The practical test is light. New twinwall transmits roughly 80 percent of light at 4 mm and less at greater thickness; a badly degraded panel can fall below 50 percent, at which point winter growing suffers noticeably even though the greenhouse still looks fine from the outside. If seedlings are stretching in a greenhouse that used to grow them stocky, aging panels are a candidate.
Does climate change the answer?
Yes, in both directions. High-UV, high-heat regions — the Southwest, Florida, high-elevation Mountain West — push panels toward the lower end of the range, because both the UV dose and the daily thermal cycling are more severe. Hail belts through the Plains and the Front Range add impact risk that no UV layer addresses; multiwall dents and corrugated sheet holds up better than thin flat sheet. Cool, cloudy, mild regions such as the Pacific Northwest and coastal New England are the gentlest, and 20 years there is realistic.
Snow load is a structural rather than a material question, but it ends panel lives all the same — a frame that deflects under snow puts point loads on panels and pops them out of their glazing bars. That is covered in anchoring a greenhouse against wind.
Related: how thick polycarbonate greenhouse panels should be, the glazing comparison in polycarbonate vs glass vs film, and whether you need a permit to build a greenhouse. Ranked structures are in best backyard greenhouse.