Decramastic Roof Tiles: Replacement and Costs in Auckland

Decramastic went on tens of thousands of Auckland houses between the late 1950s and the 1990s. The ones still up there are thirty to sixty years old and shedding their stone chip, which is the point where recoating stops being worth the money.

We strip the old panels, check the purlins and battens underneath, and lay a new long run steel roof on the same framing. Anything pre-1990s is tested for asbestos before the strip starts.

What’s included

• Full decramastic strip and re-roof
• Asbestos testing on pre-1990s panels
• Purlin and batten repair where it is needed
• Long run steel in your choice of profile and colour
• New flashings, ridge, barge and spouting
• Ceiling insulation top-up while the roof is open
• Old roofing removed and disposed of
• Fixed written quote and a 10-year workmanship warranty

If your roof is covered in small stone chips that end up in the spouting, on the driveway and in the garden after heavy rain, you have decramastic roof tiles and they are telling you something.

Decramastic went on tens of thousands of Auckland houses between the late 1950s and the 1990s. It was cheap, light and it looked like tile. The ones still up there are now thirty to sixty years old, well past the life the product was designed for, and they are failing in a predictable way.

This page covers what happens next: what it costs, what you replace it with, and the asbestos question that most roofers will not bring up.

How to tell if you have decramastic roof tiles

People often call it a tile roof, because it was designed to look like one. Check for these.

Stone chips. The surface is coated in fine stone chip, not smooth paint. If you find chips in your spouting or washed onto the path below the downpipes, that is your roof shedding.

Panel size. Decramastic comes in pressed metal panels roughly 400mm by 1300mm, each shaped to look like several tiles. Lift one at the edge and it will flex. A real concrete tile is a single heavy unit and will not.

Weight. Decramastic is around a tenth the weight of concrete tile. If the roof sounds hollow underfoot or in heavy rain, it is metal.

Shape. The original profile is scalloped along the bottom edge.

Age. If the house was built or re-roofed between 1960 and 1995 in Auckland, decramastic is likely.

If you are still not sure, send us a photo. We can usually tell from one picture of the roof edge.

Why decramastic roof tiles fail, and how long they last

A decramastic roof was built to last around thirty to forty years. Most of the ones still on Auckland houses are older than that. The metal underneath is usually fine. The coating is what goes.

Decramastic is a light steel or aluminium panel with a bitumen coating, with stone chip pressed into the bitumen while it is soft. The chip is what protects the bitumen from UV.

Over decades the bitumen hardens and loses its grip. Chip comes off, first in patches, then everywhere. Once the bitumen is exposed to sunlight it dries out and cracks. Water gets into the cracks, reaches the steel, and rust starts from the top down.

The sequence is always the same:

• Chip loss into the spouting and around downpipes
• Dull, patchy looking roof with darker bare areas
• Blocked spouting, because that chip has to go somewhere
• Rust on the exposed panels, usually worst on the sunny face
• Lifted or loose nails as the timber below moves
• Leaks, usually at flashings and valleys first

By the time it leaks, the coating has been gone for years.

Do decramastic roof tiles contain asbestos?

Decramastic made before the late 1980s can contain asbestos in the bitumen layer.

Most roofers will not mention this. We would rather tell you now than after the strip has started.

It matters because of what happens when the roof comes off. Left alone and intact, an asbestos-containing decramastic roof is not a danger to your household. Disturbed by cutting, breaking or walking on brittle panels, it can release fibres.

What we do about it. If your roof predates the late 1980s and there is any doubt, we test before anything is touched. Testing is inexpensive and takes a few days to come back.

If asbestos is present, removal is handled by a licensed removalist, not by us and not by you. Under the Health and Safety at Work (Asbestos) Regulations 2016 that is a legal requirement, not a preference:

• Testing before work begins
• Licensed removal for 10m2 or more of non-friable asbestos, or any amount of friable material
• WorkSafe notified before licensed removal starts
• Disposal at an approved site, double bagged

What it costs. Testing is a few hundred dollars. Licensed removal typically runs $3,000 to $15,000 depending on roof area and access, and it is not optional when it applies.

What it does not mean. It does not mean your house is unsafe to live in. It does not mean the job cannot be done. It means one extra step, done properly, before the new roof goes on.

Any quote for a pre-1990s decramastic roof that does not mention asbestos at all is either assuming it away or planning to raise it later.

What decramastic gets replaced with

Almost always long run steel. Sometimes modern metal tile.

Long run steel, usually Colorsteel. Continuous sheets rolled from ridge to gutter with no horizontal joins. It is the same weight class as decramastic, so it suits your existing framing without reinforcement. Fewer joins means fewer places to leak. Expect 40 years plus from a correctly specified coating. This is what most Auckland decramastic roofs become, and it is what we would normally recommend.

Modern metal tile. Stone chip again, but the modern product is a completely different build: Zincalume base, acrylic coating, stone chip, acrylic overglaze. The bitumen that caused the original problem has not been used since about 1980. If you want to keep the tile look, this is how.

Concrete tile. Possible, but think carefully. Concrete tile is roughly ten times the weight of decramastic. Your framing was never designed for it, so you are looking at an engineer’s assessment and probably structural work before anything goes on. Rarely worth it.

How much does it cost to replace a decramastic roof?

Installed, including strip and disposal of the old roof. These are indicative ranges from recent Auckland work, not a quote. A roof can sit above or below them.

New roof	Cost per m2	Life
Corrugate long run	$70 to $130	30 to 50 years
Colorsteel long run	$90 to $160	40 to 60 years
Modern metal tile	$100 to $160	30 to 50 years
Concrete tile	$90 to $170 plus structural work	50 years plus

As a rough guide, a straightforward single storey Auckland home usually lands somewhere between $18,000 and $32,000 including GST. Steeper, larger, harder to reach or more complicated roofs go above that. Small simple ones come in under it. The only number that means anything on your house is a written quote after we have been up there.

One thing that catches people out: your roof is bigger than your house. A pitched roof is the sloped face plus the eaves overhang, so at a normal Auckland pitch the roof area runs 15 to 25 percent more than your floor area. A 140m2 house is usually a 170m2 roof.

What moves the number:

• Roof shape. A simple gable is quick. Hips, valleys, dormers and changes of pitch all add flashing work.
• Access and scaffold. Single storey with a clear driveway is straightforward. Two storeys, a steep section or power lines over the roof means more edge protection, and that is a real cost.
• Timber underneath. Sound purlins and battens cost nothing extra. Rot or rust has to be put right first, usually $2,000 to $10,000.
• Asbestos, where present. $3,000 to $15,000 for licensed removal.
• Spouting. Most decramastic-era spouting is as tired as the roof, and it is far cheaper to do while the scaffold is up.
• Coating grade. Coastal and western suburbs need a higher grade than inland. Chosen for your site, not to make the quote look better.

Every figure on this page is a guide based on jobs we have done. It is not an offer, a quote or a fixed price. Your roof could come in under these ranges or well over them depending on what we find once we are on it. You get a fixed written price before any work starts, and it does not move unless the scope changes.

Can you recoat decramastic tiles instead of replacing them?

Sometimes. Usually it is buying time rather than solving the problem.

Restoration means cleaning the roof, sealing what is left of the bitumen and recoating. It runs roughly a third of the cost of replacement and can give you five to ten more years if the steel underneath is still sound.

Restoration can work if the chip loss is patchy rather than total, there is no rust through the panels, the fixings are still holding, and you have a specific reason to defer, such as selling within a few years.

Restoration is a waste of money if the panels are rusted through, nails have lifted across the roof, it already leaks, or the coating has gone across most of the surface. Coating over failed steel hides the problem for a season.

And if the roof contains asbestos, high pressure cleaning it is exactly the wrong thing to do.

We will tell you which one you are looking at, including when the answer is that your roof has a few more years in it and you should call us then.

Your framing, and why the new roof has to suit it

Decramastic is light. That is why it went on so many houses in the first place, and it means the framing underneath was built for a light roof.

Going to long run steel is like for like. Same weight class, no structural change, which is why it is the standard answer.

Going to concrete tile is not. Ten times the weight on framing never designed for it means an engineer’s assessment at minimum, and often new purlins or strengthening. That cost usually outweighs the aesthetic reason for wanting it.

Either way, the battens and purlins can only be properly assessed once the old roof is off. We quote a stated timber allowance rather than pretending the number is zero, so you can see exactly what is provisional.

The one chance to fix your insulation

With the roof off, your ceiling cavity is open and accessible in a way it will not be again for forty years.

If your house is from the decramastic era, the insulation in it is likely original, compressed, or missing in patches. Topping it up while the roof is off costs a fraction of doing it as its own job later, and it is the single cheapest comfort improvement available to a 1970s Auckland house.

We are roofers, not insulation installers, but we will tell you what we can see up there and we will leave you the access to do something about it.

Do you need building consent?

Usually not. Replacing a roof with a comparable material is normally maintenance and does not require consent.

You will likely need it if you change the roof profile or pitch, if the structure changes, or if you are going from a light roof to a heavy one such as concrete tile. Council fees run $500 to $2,000, plus engineering at $1,500 to $4,000 where the structure changes.

We will tell you which side of that line your job sits on before you commit to anything.

How the job runs

1. Look at it. We measure the roof, check the spouting and flashings, and look at the timber where we can get eyes on it. If the roof predates the late 1980s we talk about asbestos testing at this point, not later.
2. Fixed written quote. Material and coating grade named, strip and disposal included, scaffold included, spouting priced or explicitly excluded, timber allowance stated separately.
3. Testing, if it applies. A few days, before anything is touched.
4. Strip in sections. The old roof comes off in stages rather than all at once, so the house stays weathertight. Chip and panels are carted away, not left in your garden.
5. Check and repair the structure. Anything rotten or rusted gets put right before the new roof goes on.
6. Underlay, then the new roof. Breather underlay, then your new roofing with matching flashings, ridge and barge.
7. Spouting and downpipes. Renewed if you have included them, while the scaffold is still up.
8. Clean up and walk through. We go over the finished job with you before the scaffold comes down.

Most single storey decramastic replacements run three to five working days, weather depending. Asbestos removal adds time.

Get a fixed written price on your decramastic roof

We will come and look at it, tell you honestly whether it needs replacing now or in five years, and give you an itemised quote. No obligation and no charge.

Not sure if you even have decramastic? Send a photo of the roof edge and we will tell you.