The UK's bestPolycarbonate Greenhouses2022 Review

How to Choose the Best Polycarbonate Greenhouse

If there’s one thing that’s hard to predict here in the UK, it’s the weather – which probably explains our fascination with talking about it so much!

However, whilst it makes for great small-talk, such changeable weather can make growing plants and produce a little tricky.

Whilst a greenhouse can’t help control the weather, it at least makes it possible for us to regulate the growing conditions for our plants – and isn’t that the next best thing?

Polycarbonate greenhouses are affordable, relatively easy to install and have a range of benefits over glass greenhouses.

If you’re trying to choose the best polycarbonate greenhouse for your garden, the following information will help you make an informed decision:

Benefits of a Polycarbonate Greenhouse

First, we’ll look at the general benefits for having a greenhouse, before moving onto the specific benefits of a polycarbonate greenhouse.

• Warmer growing environment.

First and foremost, the air inside a greenhouse will be noticeably warmer than the air outside will be noticeably warmer than the air outside once the sun starts shining. The warmer temperatures mean you’ll be able to grow crops and plants you wouldn’t normally be able to in the UK

• Longer growing season.

On sunny days, your greenhouse will warm up very quickly. This is especially noticeable in the spring and autumn months, where the sun shines but the air still feels a little chilly. Sunny days will extend your growing season.

• Controlled environment.

The climate inside a greenhouse is far easier to control. You won’t need to worry about excessive rain, strong winds, frost or pests!

• (Usually!) no planning permission required.

In most areas, neither greenhouses nor polytunnels require planning permission as they aren’t permanent structures. However, there are some cases in which you will require planning permission – which are detailed in the FAQs.

Now, here are some of the benefits of having a specifically polycarbonate greenhouse:

• Polycarbonate has a natural UV filter and will protect plants from excessive UV rays
• Thicker polycarbonate is easy to come by and will diffuse light better than glass
• Panels won’t break or smash

There are many more comparisons to be made between polycarbonate and glass greenhouses, which will be explored further in the following section.

Polycarbonate vs Glass Greenhouses

Traditionally, greenhouses exclusively used glass glazing. However, recently, more people have been opting to use polycarbonate instead. So the question is – which is better, and what difference do the materials make?

Glass Glazing

If you favour traditional appearances, you might be keen to opt for glass. Glass greenhouses tend to have a more expensive look (which probably has something to do with the fact that they cost more!) and are a highly aesthetic option.

Practically speaking, glass allows a huge amount of light in to the greenhouse, which is beneficial for plants that thrive in bright conditions.

The pros of glass glazing are:

• It’s a traditional and attractive look
• Glass offers very high light transmission
• It won’t fade or discolour overtime
• The panels are very durable (as long as no impacts cause them to crack or shatter)
• You can recycle old glass using old windows or panes
• It’s easy to replace cracked panes

The cons of glass glazing are:

• It offers no sun protection so your plants may get too hot
• Quite a lot of energy is required to heat and cool a glass greenhouse
• It can be quite an expensive material to buy new
• Installation is challenging because panes are heavy and can break easily
• If panes do break, the broken glass can be dangerous to both humans and animals
• Needs regular cleaning to stop smudges, dirt and debris blocking light unevenly

Polycarbonate Glazing

Quickly rising in popularity, polycarbonate is a type of plastic glazing. Whilst it doesn’t have the beloved, traditional appearance of glass, there are a number of benefits. It’s also possible to buy polycarbonate glazing with varying levels of transparency, depending on what your plants need.

The pros of polycarbonate glazing are:

• It’s flexible and can withstand strong winds without shattering
• Polycarbonate offers better UV protection than glass. Whilst it still lets in warmth and sunlight, UV rays are less likely to damage your plants
• Better insulation than glass – offers a double-glazing effect that’ll keep your greenhouse warmer for longer
• Easier to install than glass thanks to the lighter weight (and the fact there’s no danger of it shattering if dropped)
• Good weather resistance
• Needs far less cleaning than glass

The cons of polycarbonate glazing are:

• It lacks the aesthetic appeal of glass
• Condensation can form between the layers of polycarbonate
• Due to polycarbonate’s lighter weight, panels can blow out if not secured in firmly enough (the greenhouse itself also needs to be firmly secured to the ground)
• Finding a replacement for a broken panel can take longer than it would with glass greenhouses

Choosing the Right Size Greenhouse

Naturally, your outdoor space will dictate what size greenhouse you can physically fit into your garden, but there are other things to bear in mind too.

A 6 x 4 ft (1.83 x 1.22 m) greenhouse is considered ‘standard size’. For most people, this will provide ample room for the plants that you wish to grow or overwinter in there.

If you have a larger garden, and don’t mind taking up a bit more room, then it’s possible to get greenhouses double the standard size, at 6 x 8 ft (1.83 x 2.44 m) – this will give you a lot more space to play with and you’ll be able to grow a lot more plants.

But, be warned: a larger greenhouse will be much harder to heat. In the winter, you may end up spending a pretty penny on heating a large greenhouse, so be sure that you actually need all that space before you go for one.

If you don’t have a lot of space available (or even if you do and you just want a smaller greenhouse unit) there are greenhouses available that are more like cabinets than walk-in buildings. These ‘mini greenhouses’ can be installed anywhere (commonly against the wall of your house) and still have enough space for several seed trays or smaller plants.

Depending on the size and layout of your garden, it may be worth knowing that not every greenhouse has its door positioned on its shorter side. Whilst that might be the more traditional layout, you can also get greenhouses that have their door positioned on the longer side making them wider rather than deeper.

Choosing the Right Style Greenhouse

There are three main greenhouse styles (for walk-in greenhouses). These are: traditional, octagonal and lean-to.

Depending on the size and layout of your garden, you may find that one style makes more sense than the others, so it’s good to have an idea about what’s available on the market.

Traditional greenhouses are the most popular choice. They’re the standard rectangular greenhouse and come in a huge range of sizes and widths to suit almost any garden.

Octagonal greenhouses have an additional aesthetic element, as well as being practical. Octagonal greenhouses can look extremely modern and create a focal point in the garden. They tend to be placed in more of a central location rather than being hidden into corners.

Lean-to greenhouses are perfect for smaller gardens, although they can work in any space. These take advantage of an existing wall in the garden, with one flat side that gets positioned against the wall. If positioned against the wall of the house, these greenhouses can benefit from some of the heat from the wall.

Greenhouse Doors and Openable Windows

Some greenhouses have a hinged door that opens outwards whilst others have a sliding door. You may even come across greenhouses that have a door at each end for easier access.

Sliding doors are one of the best options for small gardens. They slide open and closed without needing to encroach on any garden space. They’re also great in windy weather as they won’t slam or fly open, as a hinged door might.

Hinged doors can be easier to open that sliding doors, but they have the disadvantage of slamming and flapping if they are not closed properly.

When it comes to windows, these can be important for helping with ventilation in the greenhouse. If the greenhouse doesn’t have openable windows, it will need some other form of ventilation. On hotter days, greenhouses can easily overheat, which can damage and even kill a lot of your plants.

Even in cooler weather, good ventilation is required to stop damp and mildew from hanging around which could cause mould.

Polycarbonate Greenhouse FAQs

What is the best thickness of polycarbonate for a greenhouse? 

There is no set thickness that’s used for polycarbonate greenhouses. However, those made with thicker polycarbonate tend to have better insulation (but they can block more sun).

For the UK climate, a thickness of around 4 mm or more will be perfect. This tends to give a good balance of insulation and light. 

4 mm panels may not succeed in completely keeping the frost out during winter. You will likely need a heater, or thicker panels, to achieve this.

Where should I put my polycarbonate greenhouse?

It’s important that the roof of your greenhouse is able to catch direct sunlight, but it should still be installed in a slightly sheltered area. Hedges or fences will provide a small amount of shelter from very strong winds. 

Avoid installing your greenhouse near overhanging trees. Not only can these damage your greenhouse, they can also make it dirty (which can, in turn, block light). 

If you’re planning on having a water supply and electricity in your greenhouse, the location is very important. If you’d like to install a heater, lighting, grow lights, propagators or automatic watering systems, you’ll almost definitely need a water or electricity source. 

Finally, you need to consider the greenhouse’s foundation. Ideally, you’ll need a level or almost level site. Some gardeners opt to lay flag stones or slabs, which should be securely bedded. 

While many greenhouses come with a base included, you’ll still need a foundation to properly secure your greenhouse.

Do I need planning permission to install a greenhouse?

In most cases, you won’t require planning permission to install a greenhouse in your garden.

However, there are some instances where planning permission may be required. You may require planning permission if:

• Your greenhouse will be installed in an area that it’s highly visible to passers by and neighbours – for example in your front garden
• You live in a National Park
• Your house is a listed building
• The greenhouse is going to be installed within 2m of the edge of the boundary of your property
• The greenhouse is over 2.5m tall
• 50% or more of your garden is occupied by outbuildings

If you are in any doubt over planning permission, it’s highly recommended that you contact your local council.