Nobody stands on clear roofing
The metal roofing Code of Practice says translucent sheeting must not be walked on unless it's designed for it, and WorkSafe lists clear roofing alongside skylights and fibrolite as brittle. When cladding is replaced near fragile sheets, WorkSafe's roof guidelines call for edge protection around them. Look at yours from underneath or from the ground, and leave anything on top to a roofer with the right gear.
What it is
Polycarbonate is a tough, light plastic. For roofing it comes as single-skin sheets rolled to match longrun profiles, so it can sit beside a metal roof, and as multiwall sheets with hollow cells that hold a little more warmth. Clear, tinted and opal versions change how much light and heat come through.
It isn't the same as GRP (glass-reinforced plastic) sheeting such as Dimond's Duraclad, which Dimond makes in a corrugate profile. The metal roofing Code of Practice lists harsh geothermal areas among the places GRP gets used.
Clear roof or solid roof over the deck?
| Polycarbonate | Longrun steel | |
|---|---|---|
| Light | Lets daylight through | Blocks it, so rooms behind can get darker |
| Rust | The sheet won't rust, but fixings and frame can | Coating choice depends on distance from the sea |
| Walking on it | Never | Roofers only, following the maker's rules |
| How long it lasts | Depends on the sheet; get the maker's written warranty | Set out in the steel maker's warranty for your site |
Where it suits in New Zealand
Coast. The sheet copes with salt; the screws and frame are another story. E2/AS1 lists aluminium, bronze and stainless steel fixings as acceptable in every exposure zone, while hot-dip galvanised nails are limited to zones B and C, and Class 4 galvanised screws to B, C and D. Ask which zone you're in and what they'll fix with.
Hail. Some places get plenty: NIWA says Invercargill Aero averages 30 hail days a year and Dunedin Airport 12. In hail country, read what the sheet's warranty says about hail before you choose.
Snow. A clear roof carries snow like any other. The NZS 3604 maximum snow load is 2 kPa and higher sites in snow zones need specific design, so somewhere like Queenstown, which averages 12 snow days a year, needs the frame designed for it.
Wind and geothermal. Light sheets catch the wind, so fixing spacing has to suit your wind zone. Near geothermal vents, BRANZ found aluminium and grade 304 stainless steel far more resistant than other metals, worth knowing when choosing the frame and fixings.
How long it lasts, and the upkeep
We don't have a manufacturer's lifespan figure for polycarbonate roofing that we'd stand behind, and it varies between makers and grades. Ask for the written warranty and check what it covers, such as yellowing, loss of light, hail and breakage, and for how long.
Upkeep is mostly washing. Use what the sheet maker recommends, usually mild soapy water and a soft brush, and keep solvents and scourers away. Work from the ground with a long-handled brush, and check leaves aren't piling up where the sheets meet the spouting.
What makes the job bigger or smaller
Size matters, but the frame matters more. Re-sheeting a sound pergola at a pitch the maker allows is straightforward; a new frame, flashing against the house wall or a link into the main roof's spouting makes it bigger. Plastic sheets move more with heat than steel, so they need fixings that allow for it.
Before anything is ordered, ask your council or builder whether your pergola or carport needs a building consent.
What to ask before it goes up
- Which brand and grade of sheet is it, and what does its warranty cover?
- Is the frame strong enough, and is the pitch within the maker's limits?
- What fixings and washers will you use for my exposure zone?
- How should I clean it without voiding the warranty?
What you can do
You can
- Hose and brush the sheets from the ground with a soft, long-handled brush
- Look up from underneath for cracks or loose fixings
- Keep ladders from leaning on the sheets
Leave to a roofer
- Replacing cracked or yellowed sheets
- Refixing loose sheets and washers
- Flashing against the house
- Anything that means getting above the sheets
What we'd put up
For a deck you want to keep bright, we'd go polycarbonate on a sound frame, fixed with screws that suit your exposure zone, and we'd read the sheet's warranty before signing. Right on the coast or in hail country, we'd also weigh up a solid roof with a skylight before deciding.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.