As designers, manufacturers, and installers of clear roof canopies, we are often asked about the choice of glass, PVC, polycarbonate or alternative sheet material.
Polycarbonate is often the preferred choice for roofing sheets due to its higher strength feature; it doesn’t shatter like glass or fibreglass (aka glass reinforced fibre).
Glass can also be used for canopies, but is considerably more expensive. This article focuses mainly on polycarbonate and fibreglass.
Why Is Polycarbonate So Strong?
Polycarbonate absorbs impact by flexing and recovering to its original shape. In other words, its ductile nature gives it much more impact resistance than the brittle alternatives of glass and fibreglass. This makes polycarbonate the best choice for glass-like visibility for situations that require safety, security and anti-vandal shelters and rooflights.
Various forms of Polycarbonate are engineered to perform to different quality requirements. That said, however, like-for-like polycarbonate is stronger than reinforced fibreglass.
Polycarbonate is so strong, that it’s even used in bulletproof windows, safety guards and protective shields! This level of strength makes it ideal for canopies and covered walkways in public settings and schools.
|Comparative tensile strength of Polycarbonate, Fibreglass and Glass|
|Fibreglass||1.52 MPa – 55MPa||Variable, depending on glass fibre to resin ratio|
|PVC||52 MPa at 20 °C||Strength drops at higher temperatures|
GRP (Fibreglass) Roof Panels
GRP stands for Glass Reinforced Plastic (sometimes referred to as FRP (Fibre Reinforced Plastic). It is a composite of finely spun glass fibres mixed in with polyester resin.
Advantages Of GRP:
- Translucent; Not being transparent means it diffuses light and provides a degree of privacy.
- Cheaper than polycarbonate. Often used for warehouse skylights that, being inaccessible have only a minor risk of impact, i.e. being walked on or having objects fall on them.
- Scratch resistant.
- Colours – natively translucent off-white or can be dyed in other colours.
- Available with UV Stabiliser – Available covered with a UV blocking layer to extend its lifespan.
Disadvantages Of GRP:
- Panels Discolour – UV from sunlight has a yellowing effect on GRP and causes coloured panels to fade. Becomes more brittle with age. UV-protective coating or UV blocking additive is needed to lengthen the lifespan of GRP.
- Low Impact Resistance – It will shatter or snap – likely suddenly, rather than flex like Polycarbonate does.
- Shorter Life Expectancy – The life span of GRP is shorter compared to other roof panel materials.
- Rough Surface – The fibre content of this material means the surface is less than smooth, making it difficult to clean and maintain as lichen and dirt can get trapped in the texture.
- The composite mix of materials makes it difficult to recycle.
Polycarbonate Roof Panels
Polycarbonate is a lightweight, strong material that is ideal for a wide variety of applications from conservatory roofs and canopy roofs, bulletproof windows, and safety shields to CDs and eyeglasses. What makes this material stand out from similar materials is its low weight-strength ratio making it the first choice for many applications where strength is important. In a school environment, where objects could be dropped out of a first-floor window, or children might be tempted to climb on a canopy, strength is very important.
Advantages Of Polycarbonate:
- High Impact Resistance – Has a very high impact resistance, making it virtually unbreakable.
- Versatile – Polycarbonate is lighter than glass and easy to cut and form into shape.
- Naturally Clear – Can be glass-like transparent or dyed for translucent or opaque colours. Bronze is popular for shielding from the sun whilst allowing some diffused light to penetrate.
- Long Life Span – It has a long life expectancy and maintains its high strength and clean look over the years.
- High UV Protection – Polycarbonate is, to some extent naturally resistant to UV breakdown and many varieties are co-extruded (manufactured) with added UV filters to offer higher UV protection throughout.
- Cost Effective – Polycarb is cost-effective compared to other glazing options, especially when the avoidance of repair work is factored in.
- Durable and Tough – This is a strong material that has an excellent structural performance.
- Excellent Fire Performance – It is self-extinguishing when the source of the flame is removed and it will not promote fire or assist the spread of fire.
- Low Heat Transmission – Keeps the area underneath cooler in hot, sunny weather and prevents heat loss during cold weather.
- Effective resistance to weather.
- Readily Recyclable. It can be recycled again and again without losing its inherent properties. Any off-cuts from canopy fabrication can be easily recycled back into new sheets.
Disadvantages Of Polycarbonate:
- Less resistant to surface scratching than glass. Scratches in some instances could be polished out.
- More expensive than fibreglass and PVC in the short term.
Conclusion on Polycarb vs Fibreglass
The main reason fibreglass is used, is to try to cut some costs on the project. In a situation where child safety, long-term appearance and weather resistance is important, polycarbonate is the long-term winner.