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Polycarbonate Roofing Installation

Written by JD
08/05/2018 14:10:06

A Guide to Roofing: Using Polycarbonate Sheets

One of the common areas of advice we are asked about at The Plastic People is about using polycarbonate sheets for roofing. Polycarbonate sheets have been designed for both domestic and commercial roofing and there are many glazing systems that support polycarbonate sheets since its growth as a popular choice for roofing projects. Here's a picture of a DIY roofing project completed by one of our customers using multi wall polycarbonate:

Polycarbonate is perfect for roofing

Twin-wall and multi-wall polycarbonate is the plastic material that is a prevalent choice for roofing projects because it is so light making it easy to install, so strong it is virtually unbreakable and it offers some insulation too helping to keep spaces warmer in winter and cooler in summer.  Because it can be cut to any shape, polycarbonate is suitable for many styles of roofs.  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 (canopies are usually supported by your house / building to which they are attached and by two or more support posts.)

Carport with polycarbonate roof
a canopy with a polycarbonate roof

What Is Twin-wall and Multi-wall Polycarbonate
Multiwall polycarbonate is a polycarbonate with many walls or layers. Where the polycarbonate has two layers it is known as Twinwall Polycarbonate and where it has three or more layers it is known as Multiwall Polycarbonate.

 insulating layers in multiwall polycarbonate
multiwall polycarbonate has insulating layers

It is this layering combined with its weight (very light) and strength (it is virtually unbreakable) which makes this type of polycarbonate 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.
The other draw to this type of polycarbonate is the UV protection it offers along with its ability (via its layers) to diffuse light and therefore give a more even distribution of that light and heat. For these reasons, twinwall and multiwall polycarbonate is a popular choice for greenhouses, conservatories and roofing.
This proven way of reducing the intensity of the light reaching inside the rooms / greenhouse means there is also a reduction in hot and cool patches too. Research has shown that evenly distributed light can help improve crop yield and leaf count as well as preventing plant injury such as leaf burn.

Multi wall 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's how and why:

  • Twinwall/multiwall is safe - up to 200x stronger than glass, and 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 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 blocks harmful UV radiation while still allowing exceptional levels of visibility.
  • Twinwall / multiwall is easy to use - twinwall and multiwall polycarbonate is 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 offers a much nicer and longer lasting finish than corrugated sheets.
  • Choosing polycarbonate can save a great deal of money, especially if your conservatory is large.
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. Polycarbonate roof panels can be bought which already come with this insulation or the 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 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 multi-wall 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 as the thicker multi-wall polycarbonate may be unnecessary or very necessary depending on how much additional heating may be required through longer, colder winter seasons if single layer glazing or thinner twin-wall polycarbonate is used. The many different thicknesses of polycarbonate sheets, suiting 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 make careful measurements and get the right size.   You can either buy polycarbonate sheets suitable for roofing and cut them (despite its impressive strength, you can cut polycarbonate roof sheets fairly easily yourself 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 off with a basic drawing of your roofing project. To work out how much twin wall or multi wall polycarbonate your roofing project requires it is best to begin with a drawing of your roofing area. Show all sections of 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 multi-wall sheet (e.g. it will be the size of the distance between your support rafters) and play a part in how thick your multi-wall sheets should be.  Essentially the wider apart your support rafters are, the thicker the multi-wall you need to use and the narrower the width between your rafters, the stronger your roof will be.  As a guide, choose 16mm multi-wall at 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 twin-wall or multi-wall 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 do 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 necessary fixings and gaskets you require – like the ones here.

 Glazing bars for polycarbonate roofing sheets
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 which 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 bars 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.

glazing bars for canopies and patio covers

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 which is safe to use with plastic / polycarbonate. Using other sealants could crack, discolour or make your polycarbonate brittle.

When you use your multi-wall, position the sheets so that their channels run vertically which will allow for condensation (if any) to drain. Bearing this in mind, the twin-wall or multi-wall 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.  
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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