Colorado is hard on anything that sits on a roof. Along the Front Range we get hailstorms that shred vinyl siding, sun at altitude that bleaches paint, and temperature swings that can move 40 degrees in an afternoon. Greenhouse glazing, patio covers, skylights and carports take the full brunt of it.
We've supplied multiwall polycarbonate for Colorado greenhouses, barns and patio covers for decades. Here's what we've learned about choosing panels that actually last here.
Why polycarbonate beats glass and fiberglass in hail country
Glass breaks. Even tempered greenhouse glass can shatter under large hail, and broken glass overhead is dangerous.
Fiberglass (FRP) panels survive impact better than glass, but the surface erodes in UV. The fibers bloom to the surface, panels turn yellow and fuzzy, and light transmission drops within a few years.
Polycarbonate is the material that handles both hail and sun. Its impact strength is many times that of glass, and quality panels have a UV-protective layer co-extruded onto the outer face that keeps the sheet clear and tough for years. It's the default glazing for serious greenhouse growers in hail-prone regions.
Altitude changes the UV equation
UV intensity rises with elevation because there's less atmosphere to filter it. At 5,000 to 9,000 feet, a panel receives noticeably more UV than the same panel at sea level. That has two consequences:
- UV protection isn't optional. Use panels with a co-extruded UV layer, not just a UV-stabilized resin. Unprotected polycarbonate yellows and becomes brittle.
- Install the right side up. The UV-protected face is marked on the film or masking. Install it facing the sky. Installed upside down, a panel loses its protection and can fail in just a few seasons. This is the single most common installation error we see.
Twin-wall vs. multiwall: choosing thickness
Multiwall polycarbonate has internal ribs that create hollow channels, called flutes. The air trapped in those channels insulates and stiffens the panel.
| Thickness | Typical structure | Best for |
| 6 mm | Twin-wall | Cold frames, small hobby greenhouses, sheds |
| 8 mm | Twin-wall | Backyard greenhouses, patio covers |
| 10 mm | Twin- or triple-wall | Year-round greenhouses, skylights |
| 16 mm | Triple- or multi-wall | Commercial greenhouses, heated spaces, high snow load |
Thicker panels insulate better, span farther between supports and take hail better. For a heated greenhouse that runs through a Colorado winter, the jump from 8 mm to 16 mm can noticeably cut heating costs. For hail resistance alone, we steer most buyers to at least 8 mm.
We stock AmeriLux multiwall polycarbonate and can advise on structure for your span and use.
Thermal expansion: the hidden panel killer
Polycarbonate expands and contracts more than metal framing. Its coefficient of thermal expansion is about 0.0000375 inches per inch per degree Fahrenheit. That sounds tiny until you do the math:
- An 8-foot (96") panel
- A 120°F swing between a frigid January night and a summer afternoon on a dark roof
- 96 × 120 × 0.0000375 ≈ 0.43 inches of movement
Pin that panel tight and it will buckle, crack around screws or pull out of its channel. To prevent it:
- Drill oversized holes, typically about 1/8" to 3/16" larger than the screw shank, so the panel can slide.
- Use sealing washers made for polycarbonate, and snug screws without crushing the panel.
- Leave expansion gaps in channels and at panel ends, per the manufacturer's chart.
- Use H-channels and U-channels designed for the panel thickness.
Install flutes running downhill
The hollow channels must run vertically, in the direction of the slope, so condensation can drain out the bottom. Run them sideways and water pools inside, grows algae and fogs the panel permanently.
Sealing the ends correctly is just as important:
- Top edge: solid aluminum sealing tape to keep dust, bugs and water out.
- Bottom edge: vented (breathable) tape that lets moisture escape but keeps debris out.
- Then cap both edges with a U-channel or closure profile.
Never seal the bottom with solid tape. Trapped moisture is the fastest way to ruin a multiwall panel.
Plan for snow load and pitch
Colorado roofs carry snow. Purlin spacing should come from the panel manufacturer's load tables for your panel thickness and local snow load. Keep a minimum roof pitch as specified by the manufacturer so snow and water shed. A low-pitch roof that holds snow will flex the panels and stress the fasteners. If you're not sure of your local design snow load, your county building department can tell you.
Cleaning and care
- Rinse with lukewarm water and mild soap; use a soft cloth or sponge.
- Never use abrasive pads, squeegees with grit, or ammonia-based glass cleaners.
- Avoid solvents like acetone, which can craze polycarbonate.
- After a hailstorm, check for punctures and re-tape any damaged edges.
Solid polycarbonate for skylights and covers
Where clarity matters more than insulation, as in a see-through patio cover, entry canopy or skylight, solid polycarbonate sheet is an option. Choose a grade with UV protection on at least one side and, for areas people will see up close, an abrasion-resistant coating.
Get the right panel for your project
Colorado Plastic Products stocks twin-wall and multiwall polycarbonate and solid polycarbonate sheet, and we can help you source the right tapes, channels and fasteners. We cut panels to length in our shop so they arrive ready to install. Browse glazing in our online store and add it to a quote, or bring us your greenhouse or patio cover plans and we'll help you pick the thickness and accessories.
