What's actually on your roof?
Decramastic tiles are early stone-coated metal tiles. Gerard says they were popular in New Zealand in the 1960s and 1970s, made from galvanised steel with stone chips embedded in a bituminous coating, and that today's pressed steel tiles have replaced them. Plenty of Kiwis still call any stone-chip metal tile decramastic.
COLORSTEEL is NZ Steel's pre-painted steel roofing, made in New Zealand. The current range is two products: COLORSTEEL MAXAM for most environments, and COLORSTEEL ALTIMATE for extreme ones. On a house it's usually longrun, meaning long sheets running from the ridge down to the spouting (gutters), in corrugate, a trapezoidal profile or tray.
Both are light next to concrete or clay tiles, which counts in an earthquake. The Natural Hazards Commission's Quake Safe Your Home guide names corrugated iron and metal tiles as the lighter options to replace concrete or slate tiles with.
Decramastic and COLORSTEEL longrun, side by side
| Decramastic tiles | COLORSTEEL longrun | |
|---|---|---|
| What it is | Pressed steel tiles with a stone-chip coating | Pre-painted steel sheet |
| Look | Textured and tile-like, matt finish | Clean lines, smooth painted finish |
| How it usually wears | Chips wash off, coating breaks down, rust starts at tile edges and laps | Paint fades, rust starts at cut edges, laps and failed fixings |
| Typical damage | Dents and cracked coating where tiles have been walked on | Scratches, and lifted or loose fixings |
| Repairs | Single damaged tiles can be removed and replaced | Damaged sheets are usually replaced full length |
| LBP area of practice to look for | Metal tile roof | Profiled metal roof |
When decramastic is worth repairing
Decramastic wears out slowly. Resene describes the stone chips eroding over time, exposing the bitumen and eventually the galvanised steel, which will ultimately rust. Walking on the tiles makes it worse: the metal roofing Code of Practice says walking on metal tiles indiscriminately may cause considerable damage.
If the steel is still sound, a roofer can replace damaged tiles, refix lifted ones, treat rust and recoat the roof. Gerard says a single damaged metal tile can be removed and replaced, and where only a handful of tiles show corrosion it's usually straightforward to replace them once the cause is found. Resene's spec for painting aged decramastic says the paint restores colour but not the original chip texture.
Cleaning needs care. Resene says water blasting isn't recommended because it dislodges chip, and WorkSafe's safe work sheet for cleaning weathered asbestos cement and decramastic tile roofs says to apply biocide with a low-pressure sprayer and never use high-pressure spraying or blasting. Ask any roofer or painter how they plan to clean it before they start. Our page on painting a decramastic roof covers the coating side.
When switching to COLORSTEEL makes more sense
Rust coming through on tiles across the roof, chips mostly gone, and leaks that keep turning up in new places are the usual signs decramastic has had its run. Recoating tiles in that state paints over the problem for a while and little more.
A switch also suits people who want a cleaner, more modern look, or who are tired of chasing tile repairs. If you're re-roofing anyway, it's also the time to deal with underlay, flashings and spouting in one go.
If you go ahead, NZ Steel advises asking for COLORSTEEL by name, having it named in the quote and asking for a copy of the warranty. Genuine COLORSTEEL has the brand printed on the back of every sheet. There's also a middle path some owners ask about: Gerard says one of its shake profiles can be laid directly over an existing decramastic roof. Ask your roofer whether that suits your roof and what consent it needs.
What makes either path a bigger job?
Repairing decramastic is mostly about how much of the roof is affected. A few dented or rusty tiles and some sealing is a small job. A full restoration means a careful low-pressure clean, rust treatment, primer and top coats over every tile, so roof size, pitch and height matter most.
Switching to COLORSTEEL is a bigger job with more moving parts: stripping and disposing of the old tiles, any change to battens and purlins, new underlay and flashings, scaffolding, and a building consent if your council wants one. Hip-and-valley roofs and two-storey houses take longer than a simple gable.
A good written quote for either lists the scope tile by tile or item by item, says who applies for any consent, and explains what happens if rotten timber turns up once the tiles are off.
Consent, and the timber under the tiles
MBIE's exemptions guidance gives replacing an old clay tile roof with profiled metal roofing, such as longrun or pressed metal tiles, in the same position as an example of work that doesn't need a building consent, while noting that higher uplift forces must be considered. Going heavier, such as corrugated iron to concrete tiles, does need one. Some councils read a change of roofing system more strictly: Wairoa District Council says changing the roofing system or the purlins needs consent, and its example is corrugated iron to pressed metal tiles, the same switch in reverse. MBIE leaves the call with the homeowner, so check with your council, ask it for a discretionary exemption if you're unsure, and have the roofer confirm the consent position in writing in their quote.
Tiles sit on battens, while longrun is fixed to purlins, so the timber framing under the roof often changes as part of the job.
When a consent is needed, the roofing is restricted building work and must be done or supervised by an LBP (Licensed Building Practitioner). They give you and the council a Record of Work at the end, and you then apply for the code compliance certificate. Our guide on building consent for a re-roof walks through it.
Near the coast or a geothermal area
Steel roofs of either kind need the right product for the site. The metal roofing industry's Code of Practice sorts sites into corrosion categories from A (Mild) to F (Extreme Marine). It says salty sea air has most of its effect within a few hundred metres of the shore, though wind, sea conditions and the lie of the land change that.
BRANZ notes a profiled metal roof can suit a harsh coastal spot because rain washes the whole surface, while sheltered parts that rain rarely reaches corrode faster. In Rotorua, BRANZ found aluminium-zinc coated steel at its geothermal test sites showed only small rust spots after 2 years, but heavy rust close to unprotected cut edges.
Ask your roofer which exposure zone your house is in, and which product and warranty suit it. Don't treat any product as right for your spot until they've confirmed it for your address.
How to decide, step by step
Get the condition checked
Ask a roofer for photos of the worst tiles, the laps, and any rust around the edges, valleys and flashings.
Ask for two quotes
One for repairs and a recoat, one for a re-roof in COLORSTEEL, each with what's included.
Sort out consent early
If you're switching systems, ask the roofer to check with your council whether it needs a building consent, and who applies if it does.
Check the roofer's licence
For consented work, look them up on the public LBP register and check they hold a Roofing licence. Metal tile roof and profiled metal roof are separate areas of practice, so look at what they list.
Ask about the warranty for your site
Get the product and the warranty for your exposure zone in writing, plus the maintenance needed to keep it valid.
What you can do, and what to leave
You can
- Look from the ground with binoculars for bare patches, rust streaks and lifted tiles
- Check downpipe outlets for stone chips washing out
- Look in the roof space with a torch after rain for drips and stains
- Find out roughly when the roof went on
- Keep people off the tiles where you can, since footprints are where dents and leaks often start
Leave to a roofer
- Anything on the roof itself
- Low-pressure cleaning and moss treatment
- Tile replacement, refixing and recoating
- A re-roof, including any purlin changes
- Consent paperwork and the Record of Work
Our take on decramastic
If the decramastic is sound with a few tired patches, we'd repair and recoat it and get good years out of the roof you already paid for. Once rust is coming through across the roof and leaks keep moving, we'd stop spending on the tiles and get quotes for a COLORSTEEL re-roof, with the consent question settled before anyone lifts a tile.
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.