16mm Triplewall Polycarbonate

We recommend a maximum sheet width of 800mm for 16mm without extra support. The manufacturer allows wider spans at light loads, but 800mm is the safe figure for a DIY roof. That figure covers the sheet alone, not the roof structure beneath it, so check your wind and snow exposure, or call the technical team if you are unsure.

Twinwall has two skins with a single row of air channels between them. Our 16mm is a three-wall sheet: three skins and two layers of trapped air. The extra layer slows heat loss, so 16mm loses about a fifth less heat than 10mm twinwall, and the sheet is stiffer across its width. The trade-off is slightly less light.

16mm is the right choice for a canopy, lean-to or covered seating area. For a heated conservatory you sit in year round, we suggest 25mm or thicker, because 25mm loses about a third less heat than 16mm. Some customers fit 16mm over a conservatory to keep the cost down, but expect higher heating bills in winter.

Fit 16mm sheets at a pitch of at least 5 degrees, and 10 degrees or more works better for run-off. Water and leaf debris clear faster on a steeper slope. Run the flutes, the hollow channels in the sheet, down the slope so condensation drains out through the breather tape at the bottom edge.

Clear 16mm passes about 76% of daylight, bronze about 35% and white opal about 25%. Opal passes the least but spreads it evenly, removing glare and hard shadows. Choose clear where you want brightness, bronze to cut glare on a sunny aspect, and opal for a soft, even light over a seating area.

What are pre-taped edges on multiwall polycarbonate sheets?

Pre-taped edges mean that protective tapes have already been applied to the open ends of your multiwall polycarbonate sheets before delivery, saving you time during installation.

At The Polycarbonate Store, our complimentary pre-taping service is available on 10mm, 16mm, 25mm, 32mm and 35mm twinwall and multiwall polycarbonate sheets.

The two open ends of the sheet's hollow channels (flutes) are taped differently:

• Top edge – Aluminium sealing tape: Solid silver tape seals the upper end of the flutes, helping prevent water, dirt and debris from entering.
• Bottom edge – Anti-dust breather tape: Helps prevent dust and insects from entering while allowing ventilation and moisture to escape, reducing the risk of condensation build-up.

For a standard sloping roof, the aluminium-taped edge must be positioned at the top, with the breather-taped edge at the bottom, towards the gutter. The tapes should remain in place during installation.

Important: Pre-taping only covers the two open flute ends, not all four sides of the sheet. It does not replace the need for PVC sheet end closures, which should be fitted over the taped edges to provide additional protection and a neat finish. Pre-taping also does not completely prevent condensation.

During preparation, approximately 10mm of protective film is removed from each taped end. This may leave a visible preparation line, which is normally concealed by the roofing accessories. If you need to trim a pre-taped sheet, the newly exposed flutes must be cleaned and re-taped correctly before installation.

For curved roofing or other applications, the required tape arrangement may differ. Please contact us before ordering if you are unsure.

For further information, read our full guide: What Do Pre-Taped Edges Mean on Multiwall Polycarbonate Sheets?