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Guide to Polycarbonate Roofing Installation

Written by The Plastic People
08/05/2018 14:10:06

Here at The Plastic People, one of our customers' most common queries is about polycarbonate roofing panels and installation. Polycarbonate sheets have been designed for both domestic and commercial roofing - and there is a wide range of fittings and systems that support this plastic material. 

You are likely to come across polycarbonate roofing on an almost daily basis. Most commonly, it is reserved for garden fixtures and outdoor structures - such as greenhouses, patio covers, and conservatories - due to the material's strength and durability (it is 250 times stronger than glass). 

Twin and multiwall polycarbonate are the most prevalent plastic roofing material due to their cost-effectiveness, lightweight, and the fact that they are easy to work with/install. We consider polycarbonate to be a DIY-friendly material, and so, in this blog, we are going to provide you with a step-by-step guide to polycarbonate roof panels and installation! 

As our name suggests, we are mad about plastics here at The Plastic People. We cut polycarbonate - along with other plastics like acrylic (perspex) - to any shape or size. For instance, polycarbonate can be cut into triangular shapes making it suitable for gable end roofs (typically a gable is the triangular portion of a wall between the edges of a sloping roof); lean-to-roofs (typically a roof with a single slope), Edwardian and Georgian roofs as well as canopies. 

Get a cut to size polycarbonate quote here.

What Is Twinwall and Multiwall Polycarbonate?

Quite simply, when polycarbonate has two layers, it is known as Twinwall Polycarbonate; and when it has three or more layers, it is known as Multiwall Polycarbonate.

It is this layering system, combined with polycarbonate's lightweight, and virtually unbreakable strength, which make this type of plastic so popular. The more layers the polycarbonate has, the more insulation it provides. The material is often chosen because of its insulation properties. For someone taking on a roofing project, the fact that installation can be likely done single-handedly because it is so light and easy to handle is another attraction.

Multiwall polycarbonate is effective for roof glazing, conservatory glazing, carports, porches, lean-tos, orangeries, swimming pool roofs and greenhouses. It is unlike any other material. Here are some of the perks:

  • Twinwall/multiwall is safe: It is up to 250x stronger than glass - yet also much lighter. Twinwall and multiwall polycarbonates are incredibly impact-resistant. In fact, our twinwall and multiwall is bomb blast resistant! Because it is virtually unbreakable it is a safe choice for the home and public spaces.
  • Twinwall/multiwall insulates brilliantly: Twinwall polycarbonate has two thin sheets of polycarbonate separated by vertical dividing sheets; multiwall polycarbonate is the same with at least three thin sheets of polycarbonate separated by vertical dividing sheets. The thicker the multiwall, the more dividing sheets it contains. The dividing sheets give this polycarbonate a fluted appearance and structure. Air is trapped within the flutes, which prevents heat from escaping. Generally speaking, the thicker the multiwall, the higher the insulation; the thinner the twinwall/multiwall, the higher the light transmission.
  • Twinwall/multiwall provides UV protection: Our twinwall and multiwall polycarbonate almost totally block harmful UV radiation while still allowing exceptional levels of visibility.
  • Twinwall/multiwall is easy to use: Twinwall and multiwall polycarbonate are very light in weight, easy to lift/handle and cut if necessary. Polycarbonate roof panels are easy to manipulate if you are planning to build your conservatory yourself.
  • Twinwall/multiwall is low maintenance - cleaning is simple with soap and warm water.
  • Twinwall and multiwall are quicker and easier to fit than traditional glazing and offer a much nicer and longer-lasting finish than corrugated sheets.


  • ‚ÄčPolycarbonate is cheap: For particularly large buildings, such as conservatories, polycarbonate is often the most cost-effective material available to you. 

Climate Control

Keeping conservatories, summer rooms, and orangeries cooler in summer and warmer in winter is a common issue for homeowners. Polycarbonate roofing can provide an excellent solution when combined with reflective insulation. This insulation reflects the sun's heat off polycarbonate rooves and back outside, thus keeping your room cooler. Pre-insulated polycarbonate roof panels can be purchased, or insulation can be bought and added to polycarbonate yourself.

If you have a room with a glass or plastic roof that gets too hot in summer and too cold in winter, another solution is climate sensor multiwall polycarbonate. This particular multiwall polycarbonate will reduce the temperatures in your room. It works by preventing over 80% of the sun's solar energy from entering a roof resulting in up to 40 degrees decrease in internal room temperatures. And, the alternate upside: in winter, your same room will feel warmer.

Climate sensor multiwall is visually transparent as opposed to the opal effect of many other heat reflective sheets. At the same time, it still has the safety and strength benefits of normal multiwall polycarbonate.

Choosing The Right Thickness For A Polycarbonate Roof 

Twin-wall polycarbonate and multiwall polycarbonate have the same properties but offer different levels of insulation. The easy way to remember it is the more layers there are, the greater the level of insulation provided by the polycarbonate. Because of this, the more layers, the higher the cost too. 

It is important to consider how much insulation you need. Thicker multiwall polycarbonate may be necessary depending on how much additional heating is available in the space. There are many different thicknesses of polycarbonate sheets that suit different purposes. Here are some of the popular choices:

  • 4mm polycarbonate for greenhouse, cold frames and sheds
  • 10mm polycarbonate for carports, pergolas and sheds
  • 25mm and 35mm polycarbonate for conservatory roofs


How To Plan Your Twin-wall or Multi-wall Roof

Because your polycarbonate sheets need to fit between your roof joists, it is important to take careful measurements and get the right size. You can either buy polycarbonate sheets suitable for roofing and cut them (using a fine-toothed saw), or buy the polycarbonate at the sizes you need. The Plastic People can help you with either option if you would like. 

Start with a basic drawing of your roofing project. To work out how much twinwall or multiwall polycarbonate your roofing project needs, it is best to begin by drawing a diagram of your roof area. Show all sections of the wall, roof and any existing support rafters. The purpose of this is to show the size of the area that you need to cover so you can decide how many twinwall sheets you will need, or what specific cut sizes you will need to buy.

Decide where your rafters will go. If you already have support rafters in place, this will determine the size of each multiwall sheet (e.g. it will be the size of the distance between your support rafters) and play a part in how thick your multiwall sheets should be. Essentially the wider apart your support rafters are, the thicker the multiwall you need to use, and the narrower the width between your rafters, the stronger your roof will be. As a guide, choose 16mm multiwall at a minimum if your support rafters are 980mm apart. Due to varying pitch factors, wind loading and snow loading, we recommend that 1050mm is the maximum distance between rafters. 

Choose your multiwall polycarbonate sheets. Sheets come in different sizes up to 5m x 2m. It is best to use sheets no wider than 1050mm wide to allow for adequate expansion and contraction. You can buy them cut to the size you need, or you can cut them yourself using a fine-tooth jigsaw or circular saw. Think whether you would like clear, bronze or opal twinwall or multiwall polycarbonate. Opal lets in less available light, so may make a better choice if you want more shading

Select your fixings. Use your sheet dimensions as a guide to doing this – each joining sheet will require a glazing bar. You can buy gable bars where the last rafter is free standing and wall bars for the end rafters that butt against a rising wall. At the bottom slope, we recommend closing the sheets off with an aluminium end stop bar which also helps to keep the multiwall sheet even more rigid. Glazing bars are normally supplied with the necessary fixings and gaskets you require – like the ones here.


Fitting Polycarbonate Roof Sheets

Assuming you are using polycarbonate sheets for a conservatory or carport roof, the fitting of the polycarbonate sheets will be via glazing bars. Polycarbonate sheets themselves are never actually screwed to anything: they 'clip in' to a glazing system that offers you a quick and easy method of fitting.

Glazing systems typically consist of PVC or aluminium bars which have a top and bottom section. The bottom sections of the glazing bars should be screwed along the centre of your roof joists. Have your polycarbonate sheets cut to fit between them and lay them into place. The top sections of the glazing bar clip on once the sheets are in place - in effect 'capping’ the joint, and holding the polycarbonate sheets in place, allowing for expansion in hot weather and contraction in cold weather.

When you fit your polycarbonate roof, you will need a sealant to attach capping bars onto the bottom edge of your roof. Choose a non-hardening sealant that is safe to use with plastic/polycarbonate. Using other sealants could crack, discolour or make your polycarbonate brittle.

When you use your multiwall, position the sheets so that their channels run vertically which will allow for condensation (if any) to drain. With this in mind, twinwall or multiwall polycarbonate sheets can be cut, so that you get the best use of the material.

Your polycarbonate sheets should arrive covered with a protective film. This should be left on until you fit the sheet. The top and bottom end of the sheet will also be capped when the sheet is whole. If you are cutting the sheet, try to keep the top end-capping in place; cover the cut end with some perforated self-adhesive tape. A plastic cover bead can finally be fitted over the tape (with your non-hardening sealant) to capping the end.

A last important note: keep moisture from entering the flutes in your polycarbonate. If you are storing polycarbonate before use, choose somewhere dry (not outside or on wet grass).


Further Information

Visit our polycarbonate roofing area for further details on twinwall polycarbonate and multiwall polycarbonate. We have twinwall available in 6mm, 10mm and 25mm thicknesses. 

We also supply a range of garden furniture and materials, including readymade patio covers

Need some advice?

Our friendly customer services team are happy to provide specific further assistance for your project. Please let us know if we can help you in any way. Reach us via 0113 249 2222 or email.

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