Which material is best for glazing a greenhouse?

The gardening trend that blossomed during the COVID-19 pandemic still shows absolutely no signs of wilting. The renewed importance of outdoor space has led to a sustained rise in garden renovations – and a significant spike in demand for greenhouses. If you’ve been bitten by the gardening bug and are keen to enjoy a year-round growing season, investing in a greenhouse makes perfect sense. But there are a range of different factors to consider before you take the plunge. Location is key, of course, and so is size. You’ll need to consider which materials to choose for your greenhouse frame. Which leaves perhaps the most crucial decision of all: your choice of greenhouse glazing materials. Glass, clear acrylic or polycarbonate sheets are the main options, and they each have different qualities. Assessing these various choices and making the right selection can seem daunting, especially for greenhouse “first-timers”. Even if you already own a greenhouse, and simply need to renovate or repair your glazing, there are still plenty of pros and cons to evaluate.

Create the right environment

First and foremost, the greenhouse you plan to build or remodel needs to create the best environment for your plants. So before you make any decisions about which materials to use– especially for glazing – think hard about what you’re planning to grow. Will you use your greenhouse mainly to overwinter plants? Will it be used primarily for starting seeds? Will you be cultivating easy-to-grow vegetables, or higher-maintenance tropical plants such as orchids? The latter, for example, need not just heat and humidity, but also light-diffusing glazing. Some plants overheat easily, whereas others will suffer from too much shading, so your choice of greenhouse covering really is critical. Keen to mix and match what you grow? To achieve the best results, try to tailor and equip your greenhouse to accommodate your most demanding plants.

Greenhouse size and location

The size and location of your greenhouse are often interdependent. Make sure to choose a location that’s easy to access (especially in bad weather), but which also benefits from good sun exposure – south-easterly is best.

With regard to size, it makes sense to build as big as your site (and budget) allow. It sounds so obvious, but plants grow, so make sure to factor in adequate height, in addition to footprint. Of course, the bigger the build, the higher the cost. Choosing the right greenhouse glazing materials can wreck or rescue your budget, so do your sums carefully.

Climate control

Yet another factor to take into account when choosing the best material for building or updating a greenhouse is the weather. How cold do the winters tend to be where you live? Do you get a lot of rainfall, very high winds, widespread frosts, or even frequent snowfalls? Taking stock of your typical climate will help you to make the best-informed decision about both frame and greenhouse glazing materials.

A closer look at glass

Many people automatically associate greenhouses with glass. This aesthetic is certainly classically attractive, and offers high light transmission. Provided it doesn’t break, and is properly looked after, glass is also long-lasting.

Compared with modern alternatives such as acrylic sheets and polycarbonate cut to size, however, using glass for a greenhouse has a number of disadvantages. The primary drawback is cost. Glass is expensive to install, and requires a lot of time and effort in terms of site prep prior to installation. Glass manages to be heavy, awkward and delicate all at the same time, making assembly a tricky and potentially dangerous prospect for any DIY greenhouse builder. It also needs regular maintenance, and it’s pricy to repair – a key consideration if your greenhouse is going to be sited near trees, or is likely to be subjected to high winds and hailstorms.

Another significant shortcoming of standard glass is that it provides virtually no insulation, heat protection or diffusion. This means you’ll probably have to invest in shade cloths in order to keep certain plants healthy. You’ll also have to spend more to cool/heat a glass greenhouse, depending on the time of year. Double, or even triple-paned glass can help to address these issues, but these options are even more expensive to install than single glass panes. They also need to be sealed properly in order to prevent the build-up of condensation.

Glass at-a-glance guide
Pros: Traditional appearance, high light transmission
Cons: Expensive, heavy, prone to damage, low heat protection/diffusion/insulation, dangerous when broken

The advantages of acrylic

Clear acrylic sheets (also known as Perspex, which is a brand name) have become a popular alternative to traditional greenhouse glass, with good reason. This material incorporates many properties that make it perfect for greenhouse glazing. Compared with standard glass, it’s less expensive, both to fit and maintain. Acrylic sheets are much stronger and more durable, with up to 20 times the impact resistance of glass. This obviously means that acrylic greenhouse glazing is much less prone to damage – good news for both new-builds and greenhouse repair scenarios. Large acrylic sheets are more tolerant to pressure than panes of glass, and are far more likely to flex than break or shatter. Despite their strength, acrylic sheets are lightweight, easier to install than glass, and need less support to hold them in place.

The advantages don’t end there. Acrylic is weather-resistant, but still offers excellent light transmission and transparency. As acrylic sheets are thicker than glass, they also provide better light diffusion, which helps to limit overheating and plant damage. Despite their thickness, they don’t look milky or cloudy, which is often the case with thicker panes of glass glazing. Acrylic sheets even incorporate a natural ultraviolet filter, which protects plants from exposure to harmful radiation.

In terms of sizing, acrylic is a hugely versatile material. Cast acrylic is commonly used for glazing, signage and retail displays. Extruded acrylic is commonly used for lighting applications, interior decoration and screening. The sheets we offer are available in a variety of different thicknesses, and can be pre-cut to your exact measurements. In addition to greenhouse glazing, acrylic is also widely used for cold frame and cloche glazing.

Acrylic at-a-glance guide
Pros: Cost-effective, strong, durable, lightweight, good light diffusion, UV protection, recyclable, guaranteed against discolouration for 10 years
Cons: Not biodegradable

The positives of polycarbonate

Polycarbonate sheets are yet another excellent option for greenhouse glazing. Available in both rigid and flexible grades, polycarbonate is a tough, transparent plastic with excellent impact resistance. It’s even more durable and damage-resistant than acrylic, so if longevity is your main priority, either for a new project or for an existing greenhouse repair, this is the material to choose.

Over 200 times stronger than standard glass, polycarbonate is almost unbreakable, making it ideal for greenhouse glazing. The fact that it is so durable makes it a great long-term investment. Polycarbonate sheets tend to be slightly more expensive than their acrylic counterparts but are still less expensive – and easier to install – than glass.

Like acrylic, polycarbonate lets the light through, but keeps the elements out, protecting the plants inside your greenhouse. It can withstand all sorts of harsh weather, including snow and heavy rain. In comparison with glass, polycarbonate retains heat better, and offers more light diffusion. It’s also lightweight, and easy to move around and manipulate.

Our polycarbonate sheets are available in a variety of different thicknesses and commonly used standard sizes. Alternatively, they can be pre-cut to your exact measurements, ready to be fitted. In addition to greenhouse glazing, polycarbonate is also ideal for shed, summer house and playhouse windows.

Polycarbonate at-a-glance guide
Pros: Extremely strong, durable, lightweight, good light diffusion, weather-resistant, recyclable
Cons: Cheaper versions may yellow over time (the Polycarbonate we supply is guaranteed for 10 years)

Keen to find out more about our plastic glazing portfolio? You can contact us here.