Choosing a Suitable Glazing Material and How It Will Affect Your Conservatory

Glass versus Polycarbonate

orangery-conservatory-1As we touched upon in the Conservatory Roofing section, the choice of glazing material will have a tremendous impact on all aspects of the conservatory – from aesthetics to comfort levels, practicality, energy efficiency, maintenance and also the initial costs.

The greatest factor influencing your personal choice of conservatory glazing material will probably vary slightly depending on the proposed usage of your new conservatory, but for most situations where the room will be used regularly throughout the year we would envisage that glass would be the preferred material. Polycarbonate sheeting offers numerous benefits such as being lightweight, easier to handle, and safer in some situations but it lacks the fundamental clarity and quality that glass affords to a conservatory. Glass units are generally more thermally efficient than all but the highest grades of polycarbonate.

Polycarbonate is a very popular option however and accounts for a significant percentage, perhaps even the majority of new conservatory glazing installations. It can require more care and cleaning than glass (at least twice per year) and does have more of a tendency to accumulate green slime in certain scenarios. Improperly carried out installations can also result in discolouration and unwanted contaminants within the cells of the polycarbonate itself, particularly around the edges.

If you were planning to use your conservatory simply for growing or cultivating plants or for occasional use then you may find that a polycarbonate roof would indeed be adequate, but for prolonged and repeated use as a comfortable living area glass is typically preferred – it is considered more hardwearing and secure in addition to its better aesthetic and energy efficiency properties. A glass roof will also have far better sound-insulation characteristics than polycarbonate, and so if you are looking to create a more peaceful space in which to relax, you will almost certainly require glass over polycarbonate for your conservatory roof. Additionally, polycarbonate tends to carry sound from impact a little too well – moderate to heavy rain or hail storms can make a polycarbonate-glazed conservatory a very noisy place to be.

It is now possible to purchase self-cleaning glass, or to have a variety of coatings applied to the exterior surface of the glazing units, for example to reduce glare or to reflect a large proportion of the heat from the sun, thereby keeping your conservatory at a more comfortable temperature on hot summer days, especially useful for south-facing conservatories.

Coatings can also be applied to give the glazing a slight tint, such as a bronze or grey tint, allowing you to further customise the look and feel of your conservatory to suit your tastes. Likewise, polycarbonate can be obtained in a variety of tints or shades. Even ‘clear’ polycarbonate bears no resemblance to glass and is not particularly clear – it diffuses the light that passes through it. You would not be able to sit under a polycarbonate-glazed roof and look at the stars in the night sky, for example.

Additionally there are aftermarket films, coatings and inserts that can be applied to glass and polycarbonate glazing to modify their characteristics and tune the thermal behaviour to suit your needs. Coatings that reduce glare or solar impact may also lengthen the life of your conservatory furniture and soft furnishings and reduce fading caused by intense exposure to the sun.

Modern low-emissivity glass such as Pilkington K Glass and their Suncool range of products have a microscopic coating that allows them to reduce heat loss to the outside by reflecting it back in to the room while also reducing the amount of radiant heat allowed into the conservatory from the sun. Further effciency gains can be made by filling the glazing units with inert gases such as Argon or Xenon which provide slightly better insulating properties than air.

There are a range of products made specifically with the conservatory application in mind, even allowing you to incorporate special glass with better soundproofing characteristics into double-glazed units. Specifying high-tech glass in custom double-glazing units is also possible and would allow you to specify a low-emissivity coating on self-cleaning glass with high soundproofing capabilities for example.

Glazing energy efficiency – the U-value

Before looking at the relative benefits of the various units available it is important to understand the units used to measure and quantify heat loss through a given product.

You will often see something called a “U-value” alongside glazing and insulating products and this is an indication of how well the material transfers heat – in this case how well the chosen glazing product will allow heat to leave your home in cold weather and indeed enter your home in warm weather.

The higher the U-value, the poorer the insulation qualities of the material in question.

At the risk of turning this into a physics lesson, the U-value is a scientific value derived by considering the amount of energy (heat) in Watts transmitted or ‘lost’ through 1 square metre (m²) of the material in question where the temperature differs by 1 degree on the Kelvin scale* (K) between the two sides of the material.

The U-value is often just quoted as a number without the unit of measurement, but the unit of measurement for the U-value is W/(m²K).
Looking at the U-value for a number of different glazing options we can see the difference in thermal efficiencies (lower is better):

Standard float glass (single glazing) 5.0
Pilkington Optifloat clear glass (standard float glass, DG) Air-filled, 2.7       Argon-filled, 2.6
Pilkington Suncool (solar control, DG) Air-filled, 1.4       Argon-filled, 1.1
Pilkington Activ Suncool (self-cleaning & solar control, DG) Air-filled, 1.3       Argon-filled, 1.1
16mm polycarbonate 2.6
25mm polycarbonate 1.6
35mm polycarbonate 1.5


A conservatory glazed with standard single-pane float glass, standard float-glass double-glazing units or 16mm polycarbonate is clearly going to prove more expensive to heat than a conservatory glazed with optimised glazing products aimed specifically at the conservatory market, or for that matter 25mm or 35mm polycarbonate and will also be subject to more pronounced temperature fluctuations on sunny days with more radiant heat entering your conservatory.

U-Values for Pilkington glass above assume standard 16mm double-glazing units.
*Degrees on the Kelvin scale of measurement have the same magnitude as Degrees Celsius or ºC, however the scale begins at 0, which equates to -273 degrees Celsius, also known as Absolute Zero. 1K=1ºC.

Choosing a conservatory – next steps

After having perused our comprehensive conservatories section, it is likely that you will want to start evaluating conservatory prices and the various styles available so you can make a more considered decision.

The best way to get started is to select around 3 different FENSA registered specialists and arrange for them to come to your home and show you the range available, and advise you on how best to make use of the space in which you are planning to erect your conservatory – they may be able to offer size or layout options that you hadn’t even considered as well as specific conservatory planning permission or building regs information relevant to your particular project.

Conservatory Quotes

One of the more established names, Anglian, have been making and installing high-quality products since 1966 and offer a 10 year warranty on all uPVC products and a 15 year warranty on gas-filled sealed glazing units for peace of mind with your new conservatory. You can request a free Anglian quote by clicking here.