Glass vs Polycarbonate

Glass vs. Polycarbonate

There is a range of different glazing options for greenhouses and to be honest they all have advantages and disadvantages when compared. The right glazing for your greenhouse will be determined by your requirements, personal preferences, climate and budget.

So, what are the main differences at a glance?

Glass

Advantages
  • Longevity
  • Traditional look
  • Light clarity
 
Disadvantages
  • Fragile and less forgiving to knocks
  • Poor thermal efficiency (3mm glass R=0.95 and 4mm glass R=1.0)
  • Potential to burn plants due to the level of clarity
 
What to look out for
  • Be sure you get toughened safety glass, otherwise it will be a hazard
  • 4mm is significantly stronger than standard 3mm

 

See our range of 4mm Tempered Glasshouses

Polycarbonate

Advantages
  • Good thermal efficiency (6mm Twinwall R=1.54). Keeps the warmth in longer into the night and offers better frost protection
  • Very tough and durable
  • Good longevity (provided it is a premium grade polycarbonate)
  • Produces a slightly diffused light which helps prevent burning/scorching the plants
 
Disadvantages
  • Prone to scratching
  • The flutes in the twin-wall can attract moisture, mould and bugs - if not sealed sufficiently in the frame. (Winter Gardenz Greenhouse flutes are all sealed with rubber beading)
 
What to look out for
  • Be sure the polycarbonate is made from virgin materials from a reputable supplier (i.e. Bayer, GE, Sabac etc.) and is not recycled
  • Ensure polycarbonate is UV treated on both sides (otherwise it will only last 1-2 years)
  • Don't touch cheap imported polycarbonate it will not survive in harsh conditions

 

See our Range of Polycarbonate Greenhouses

The differences fully explained (the low-down!)

A full, independent report, covering an overview of the glazing, advantages and disadvantages. There is also a chart comparing the thermal effectiveness of glass (both 3mm float and 4mm toughened glass), polycarbonate and plastic film, and what glazing products to avoid. Enjoy.


Traditional Classic Glass

Glass has been the preferred traditional glazing because of its permanence and beauty. However, glass is one of the least efficient materials for retaining heat due to its high heat transfer rate (i.e. allowing the cold temperature to transfer though the glass very easily) and poor insulating characteristics.

Greenhouse manufacturers offer a range of glass grades but we recommend you avoid the 3mm float glass as it is extremely dangerous due to its brittle, fragile and unforgiving nature.

If you've made up your mind that glass is your preferred glazing then we recommend you opt for a 4mm toughened safety glass. Although it's more costly it does provide slightly better thermal efficiency than the 3mm float glass, and will more than likely last a lot longer due to its strength and durability, while still providing you the traditional clear glass look that you want.

As glass is significantly heavier than other glazing alternatives, the greenhouse frame will obviously need to be substantially stronger and designed specifically for glass.

Advantages
  • Longevity
  • Traditional look
  • Light clarity
 
Disadvantages
  • Fragile and less forgiving to knocks
  • Poor thermal efficiency (3mm glass R=0.95 and 4mm glass R=1.0)
  • Potential to burn plants due to the level of clarity

"As glass is significantly heavier than other glazing alternatives, the greenhouse frame will obviously need to be substantially stronger and designed specifically for glass"

SEE THE WINTER GARDENZ GlassHOUSE RANGE

Thermal Efficient Polycarbonate

Polycarbonate (Twinwall) UV treated polycarbonate provides better clarity than Polyethylene film and nearly as much as glass (at about 89% clarity). It is also significantly stronger and more durable, making it a practical and increasingly popular choice for today's greenhouse growers.

Polycarbonate twinwall has a double layered configuration, separated by flutes. This provides a double glazing effect and improves the thermal efficiency of this product. Domestic greenhouse manufacturers often use a 6mm Polycarbonate twinwall glazing, while commercial greenhouses are commonly being constructed using 10mm, 16mm or 20mm twinwall or tri-wall polycarbonate. If polycarbonate twinwall is your preferred glazing, make sure the greenhouse frame is designed to accommodate the panels securely, ensuring they won't blow out and are sealed around the edges to maximize the thermal efficiency of this glazing product, and also keep the moisture, mould and bugs out of the inner cavity.

When choosing a greenhouse that is glazed with Polycarbonate twinwall ensure the supplier is providing quality polycarbonate from a reputable manufacturer. From our experience we find Polycarbonate glazing from the USA or Europe is of a very good grade and lasts very well (16 to 18+ years) however polycarbonate sheet coming from China is failing very quickly and usually requires replacement within two years.

Advantages
  • Good thermal efficiency (6mm Twinwall R=1.54). Keeps the warmth in longer into the night and offers better frost protection
  • Very tough and durable
  • Good longevity (provided it is a premium grade polycarbonate)
  • Produces a slightly diffused light which helps prevent burning/scorching the plants
 
Disadvantages
  • Prone to scratching.
  • The flutes in the twin-wall can attract moisture, mould and bugs - if not sealed sufficiently in the frame.
 

There are various grades of polycarbonate and not all polycarbonate is created equal. If you are considering a greenhouse that has polycarbonate glazing then make sure the polycarbonate is made from new raw-material and not recycled material, as this has a huge impact on the life of the polycarbonate. Also ensure the polycarbonate has UV protection as it will prematurely fail if this has been overlooked. You can be assured that when you buy a Winter Gardenz Greenhouse it is glazed with a premium grade polycarbonate that is made from virgin resin with UV protection on both sides. This glazing will last you 15+ years before placement is required.

"You can be assured that when you buy a Winter Gardenz Greenhouse it is glazed with a premium grade polycarbonate that is made from virgin resin with UV protection on both sides. This glazing will last you 15+ years before placement is required"

SEE THE WINTER GARDENZ GREENHOUSE RANGE

Greenhouse Insulation Ratings and Effectiveness

3mm Float Glass                              R=0.95
4mm Toughened Safety Glass      R=1.00 
200-micron Polyethylene Film          R=0.83
4mm Polycarbonate Twin-wall          R=1.43
6mm Polycarbonate Twin-wall       R=1.60   

The 'R' Value is the common unit of measure for the effectiveness of thermal insulation. The larger the number, the higher the insulation value and therefore the better heat retention.

Glazing Products to Avoid

  • Acrylic plastics, such as Perspex. This does not last when exposed to UV, and usually shows signs of deterioration within 2-3 years.
  • Cheap imported Polycarbonate and polyethylene films. Usually made from inferior grades of materials (such as recycled plastics, re-grind, etc...) and sold as new material. Typically film or polycarbonate sheets made from these low grade raw materials will not last more than two years, despite what some greenhouse importers promise.
  • You get what you pay for! Our advice to you is to make sure you buy a premium grade of glazing from a company with a reputable brand.
 

Spectral Transmittance of Rigid Materials vs. Plastic Coverings

Spectral transmittance of selected rigid greenhouse covering materials. Greenhouse Coverings
Spectral transmittance of selected film greenhouse covering materials.