Polycarbonate conservatory roofs

Polycarbonate roofs are good at two things: they are the cheapest roof you can fit, and the quickest to replace, often in a day or two. They are poor at what most people want from a conservatory. Which? says polycarbonate is less thermally efficient than glass, noisier when it rains and lets through less light, and its experts warned it could be a false economy.

If your roof is leaking, cracked or discoloured and the room is mainly for spring, summer and autumn, new sheets are a sensible low-cost fix. If you want a room you can sit in comfortably in both January and July, price the alternatives before you re-sheet.

What is a polycarbonate conservatory roof?

It is made of multiwall sheet: extruded plastic with several internal walls that trap air, and a UV-protective layer on the outer face. The sheets sit in aluminium or uPVC glazing bars with the flutes running downhill. The ends are taped, solid tape at the top and breather tape at the bottom, which Brett Martin says keeps moisture and dust out of the channels.

It is light, at 1.7 to 3.9kg/m² for Brett Martin’s range from 10mm to 35mm, and Ultraframe describes it as up to 200 times stronger than glass and virtually shatterproof. That lightness is also why frames built for polycarbonate may not be strong enough for a heavier roof later.

16mm, 25mm or 35mm: which thickness?

More thickness and more internal walls mean better insulation but less light. Brett Martin’s published figures for its clear Marlon ST sheet:

Ultraframe quotes 1.7 for its own 25mm sheet and 1.3 for 35mm. For comparison, good roof glass is about 1.0 and a new solid roof in England has to reach 0.15. Online supplier Clear Amber describes 16mm as its most popular thickness for conservatories, but 25mm or 35mm insulates noticeably better. Our guide to polycarbonate thickness goes into the detail.

Clear, opal, bronze or Solarguard?

The tint controls glare and heat. Ultraframe’s figures for its 25mm sheet:

Opal is milky and diffuses the light. Bronze and Solarguard cut heat sharply but make the room gloomy. Brett Martin says its Solar Control sheet reduces temperatures by up to 13 degrees C compared with clear, and Exolon sells an opal heat-reducing sheet called IQ-Relax. These are makers’ claims, not independent tests.

Re-sheeting or a whole new roof?

Re-sheeting keeps the existing glazing bars. The installer removes the top caps and end caps, lifts out the old sheets, checks the bars, rafters and seals, fits the new sheets and refits the caps. Ultraframe warns that top cap clips are likely to break when the caps come off and will need replacing. In one supplier case study, Omega Build replaced the glazing bars as a precaution because the originals were at least 10 years old, so ask whether yours are being reused.

It is also the one roof job homeowners regularly do themselves. One DIY blog describes two people re-sheeting a lean-to with 25mm sheet in a full day in 2016, reusing the flashing, for £324 in materials. The authors advise cutting sheets no wider than 700mm and fitting breather tape at the lowest point. Our guide to replacing a conservatory roof yourself covers the safety side.

A new roof, bars and all, makes more sense if the bars are damaged, if the ridge or box gutter leaks, or if the roof is a Synseal Global or K2. Both makers have gone, and parts for those roofs are scarce or no longer made.

Sheet makers you will come across

• Brett Martin Marlon ST: the widest range found, 4mm to 55mm, including Solar Control and two-colour tints. The warranty is described only as limited.
• Exolon multi UV (the range formerly sold as Makrolon): 10-year warranty on weathering, hail and UV stability.
• Ultraframe polycarbonate: 25mm and 35mm sheet supplied with Ultraframe roofs, with a 10-year guarantee on 25mm.
• Clear Amber Axiome: sold online, supply only, cut to size.

ExpertSure notes that some sheets carry only a 5-year guarantee, so check what yours comes with.

Who polycarbonate suits, and who it does not

Polycarbonate suits a tight budget, a leaking roof that needs fixing now, a utility room or lean-to used mainly in the warmer months, or a stopgap while you save for something better.

It suits less well if you want to use the room all year, if it faces south, or if rain noise already bothers you. ExpertSure calls rain noise the most-cited complaint. For not much more money, insulated roof panels start from about £1,800 on a medium conservatory and cut noise and heat loss, while a glass roof keeps the light with better insulation. We compare the first option directly in polycarbonate vs insulated panels.

Questions to ask before you sign

When you get quotes, ask each installer:

1. What thickness and wall structure is the sheet, and what are its U-value and light figures?
2. Which tint, and can I see a sample in daylight?
3. Are the glazing bars, top caps, end caps and seals being replaced or reused?
4. Is breather tape fitted at the bottom of every sheet?
5. What guarantee comes with the sheets, and does it cover discolouration and hail?
6. Would glass or insulated panels fit my frames, and at what price, so I can compare?

See the polycarbonate roof cost guide for typical prices by size.