Which greenhouse: Glass or polycarbonate?

Glass or Polycarbonate ?

One of the most frequent questions asked by greenhouse buyers who are new to greenhouses is “What’s best glass or polycarbonate?”. Traditionally greenhouses have always been glazed in glass both in the UK and abroad. In Germany for instance they have used frosted glass as it has the added feature of difusing UV rays !
However times are changing and so is the way we glaze our greenhouses. On the continent it has been common to use polycarbonate instead of glass and increasingly that is becoming the case here in the UK.

Polycarbonate Glazing for Greenhouses

The main advantage of polycarbonate over glass is its durability and strength and hence its safety benefits. Most greenhouses are glazed in 3mm horticultural glass which can be dangerous if broken as it breaks down into large shards which are extremely sharp. It is generally recommended that if the greenhouse is sited in a public place (allotment) or certainly where children or elderly people may be present that Toughened Safety Glass (to BS6206) or polycarbonate be used. Whilst toughened safety glass can still smash it breaks down into small pebbles like car windscreens or telephone box glass which is less dangerous that the shards of sharp glass with 3mm horticultural glass. Find a full range of leading brand toughened glass greenhouses at Greenhouse Stores.

greenhouses for sale


Polycarbonate glazing is highly recommended if you have children or animals running around your garden as any impact will merely result in the child or dog/cat bouncing of the polycarbonate panel or at the worst popping a panel out which can be put back in place simply and quickly. A collision of this type with a glass greenhouse or coldframe would result in serious injuries.

Grow Master 8×6 Greenhouse with 4mm Twin Wall Polycarbonate

Grow Master Greenhouse

Glass versus Polycarbonate

Polycarbonate greenhouses are also ideal for allotments and many local authorities now insist that allotment tenants use polygarbonate greenhouses rather than glass as part of their health and safety policy. Unfortunately greenhouses in gardens and allotments can also fall victim to vandalism and this is where polycarbonate has a very clear advantage over glass in that the cost of replacement polycarbonate is far cheaper and easier to source than glass. Generally speaking polycarbonate doesn’t smash so whether the wind has blown out a panel or a local vandal has knocked out a panel then it can simply be put back in and be secured with clips or glazing strips.
The insulation properties of polycarbonate are excellent. The most popular form of polycarbonate and by far the most effective greenhouse polycarbonate is 4mm twin wall polycarbonate sheet. This polycarbonate has a thermal insulation “R value” of around 1.42 whereas horticultural glass has an “R value” of around 0.93.
4mm twin wall polycarbonate also out performs glass where protection of your plants from harmful scorching UV is concerned also as it effectively diffuses light coming into the greenhouse whilst maintaining 80 to 85 % light transmission.
Polycarbonate greenhouses are becoming cheaper to buy with the advent of the “grow your own”  trend and it’s possible to get yourself set up with a polycarbonate greenhouse from around £200. All major greenhouse manufacturers now offer polycarbonate glazing as an option on their greenhouses and some manufacturers such as Gardman and Palram specialize in polycarbonate greenhouses.

Palram Harmony 6×4 Greenhouse with Clear Polycarbonate Glazing

palram harmony 6x4 greenhouse

Toughened Glass Greenhouse

A toughened glass greenhouse is the perfect choice for many greenhouse gardeners that live in temperate climates like the UK where the greenhouse may be exposed to high winds. Because toughened glass is supplied in one sheet (long pane) that goes from floor to eaves it is nice and heavy, it’s also generally thicker than normal greenhouse glass at 4mm. The extra weight in toughened glass gives your greenhouse much greater resistance to high winds and will stop your greenhouse frame from moving and twisting as the heavy glass keeps each section “square” under wind loads. Of course the biggest advantage of glass over polycarbonate is that you can see inside the greenhouse from the outside, therefore you can be looking down your garden from inside your house and still gaze lovingly at your tomatoes ripening !

Vitavia Jupiter 8×12 Toughened Glass Greenhouse

Vitavia jupiter 8x12 greenhouse

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