Choosing a Hamilton Roofer: Tear-Off vs. Overlay Explained
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Getting quotes for a new metal roof? One of the first things to check is whether the old roof is coming off. This guide explains why it usually should, what happens at each stage of a metal roof replacement, and what can turn up underneath.
Short answer: on a profiled metal re-roof, strip the old roof. NZ Metal Roofing Manufacturers says the existing underlay should be replaced and recommends no more than one layer of underlay on the roof. Stripping also lets the roofer check the battens and purlins and remove old nails and lead. Most Waikato homes are re-roofed this way in 2–4 days.
Quick Verdict: Tear-Off vs. Overlay
A tear-off costs more in labour and disposal, and it’s noisier. In return, you get a new roof on framing someone has actually checked. An overlay saves that work, but it leaves the old underlay, fixings and any hidden damage where they are.
Understanding Roof Tear-Off vs. Overlay
What is a Full Tear-Off?
In New Zealand, this is usually just called stripping the roof. The old iron or tiles, the nails or screws, the flashings and the underlay all come off. The framing is checked and repaired, then new underlay, steel and flashings go on.
What is a Roof Overlay?
An overlay puts a new roof on top of the old one without stripping it. Much of the advice you’ll find online is from North America, where it means a second layer of asphalt shingles. Those are uncommon on New Zealand homes, so it rarely applies here. The main local exception is metal tiles: NZQA’s trade training standard for re-roofing metal tile roofs covers them as an overlay option, with advantages and disadvantages against a complete re-roof.
Why the old roof comes off
The underlay needs replacing. NZ Metal Roofing Manufacturers’ Bulletin BU01 says that when re-roofing with profiled metal, “it is important that existing underlay gets replaced.” Doubling up can restrict water vapour leaving the roof space, which can lead to condensation and mould. New insulation rules have made this problem more common, so the bulletin recommends a single layer. Replacing it means the old roof has to come off.
The framing can’t be checked otherwise. The Code of Practice says the supporting structure should be inspected before installation, with purlins in a true plane and securely fixed. You can’t do that through an old roof.
The new fixings need something solid. Timber purlins generally need a screw to go in 30 mm. Rotten or split timber won’t give that hold, and over an old roof the installer can’t see what the screw is going into.
Old nails and lead should go. Until 1980, New Zealand roofs were fixed with lead-head nails, which back out over time. The Code says lead is incompatible with modern metallic coatings.
What happens in a metal roof replacement, step by step
Measure and written quote. The quote should name the steel, profile, colour and thickness, and say what happens to the old roof and the underlay. See how to compare re-roof quotes.
Site set-up. Scaffold or edge protection goes up to stop people and materials falling, and the sheets and a skip or truck arrive. Move anything stored in the ceiling space first. See can we stay home during a re-roof?
Strip, one section at a time. Roofers strip only what they can close in again the same day, so the house shouldn’t be open to the rain overnight. This is the noisiest stage.
Check the framing. Any battens or purlins that are soft, split or loose are repaired or replaced before anything new goes on.
New underlay. On lined homes, the Building Code requires a permeable, absorbent underlay under profiled metal roofing. The Code of Practice recommends a synthetic, self-supporting, fire-retardant type for houses.
New sheets and screws. Longrun sheets run in one length from ridge to spouting. Exposed fixings must be at least Class 4, with sealing washers. Sheets are cut by shear, not with friction blades, which throw hot metal particles into the coating.
Flashings and penetrations. Ridges, hips, barges, valleys and aprons are finished, along with chimneys, flues and skylights. New spouting goes on now too, if it’s part of the job.
Clean-up and paperwork. Metal filings (swarf) rust and stain the new paint if they’re left, so the Code says to sweep them off at least at the end of every day. Gutters, valleys and the roof should be left clean. Keep your invoice and warranties with your house papers, along with the Record of Work if the job was consented.
Most homes take 2–4 days on site. Rain, two storeys or rotten timber can add time. See how long does a re-roof take?
What can turn up under an old roof
What you might find
Why it matters
What usually happens
Lead-head nails
Used until 1980. They back out, and the shanks corrode.
Removed. New screws go in.
Soft or split battens and purlins
They can’t hold a fixing properly.
Replaced at the rate agreed on the quote.
Old underlay, or none
Older homes can have tired underlay or no underlay at all.
New single layer of compliant underlay.
Old lead flashings
Lead isn’t compatible with modern coated steel.
Removed. New flashings are made to fit.
An unused chimney
It needs new flashings if it stays.
Removed below the roofline or re-flashed. Decide before the quote.
Possible asbestos
WorkSafe says buildings built before 2000 are likely to contain it, including in fibre-cement soffits and older roofing.
Similar for iron to steel, and lighter for tiles to steel
Old roof plus new roof
Upfront labour and disposal
Higher
Lower
Noise and waste on site
More
Less
Pricing for a Full Tear-Off
Stripping and disposal are part of a normal re-roof price, so they should be a line on your quote. Most Waikato homes cost about $18,000–$40,000 to re-roof in COLORSTEEL MAXAM®, or roughly $110–$220 per m². Old iron comes off quickly, so a single-storey, three-bedroom home going from iron to corrugate is typically $18,000–$26,000. Concrete tiles are about ten times heavier, and the same size of home going from tiles to steel is typically $28,000–$40,000. See what a metal re-roof costs.
If one quote is much lower than the others, check whether the old roof and underlay are being removed at all.
Which Should You Choose?
For a profiled metal roof on a lined home, choose a full tear-off. If a roofer suggests going over the top, ask these questions:
What happens to the old underlay, and how will the roof space vent?
How will you check the battens and purlins?
What will the new screws fix into, and how far will they go in?
Does the manufacturer’s system and warranty allow it? Can I see that in writing?
Does the job need a building consent? Like-for-like replacement usually doesn’t, and Hamilton’s rules are here. Ask the council if the work is anything else.
How CTR Roofing replaces a roof
A CTR re-roof starts with the old roof coming off. We use COLORSTEEL MAXAM® on every job, our installers hold LBP Roofing licences, we supply a Record of Work on every consented job, and most homes are done in 2–4 days. We’ve been roofing in the Waikato since 2010 from our yard in Frankton, Hamilton, and we’re a RANZ member. See metal roof replacement in Hamilton and the Waikato.
Planning a metal roof replacement?
Tell us about your roof and we’ll be in touch. COLORSTEEL MAXAM® on every job, and most homes are re-roofed in 2–4 days.
Can you lay a new metal roof over old iron?
It’s not recommended for a profiled metal roof. NZ Metal Roofing Manufacturers says the existing underlay should be replaced on a re-roof. Going over the top also means the battens, purlins and old nails can’t be checked or dealt with.
Can you put a metal roof over shingles?
Asphalt shingles are uncommon on New Zealand homes, so this mostly comes from North American advice. The same concerns apply here: the old underlay stays, the framing can’t be checked, and the new fixings go through the old roof. Check any overlay against the manufacturer’s installation requirements first.
Is a roof overlay always cheaper than a tear-off?
Upfront, it should cost less because there’s less labour and disposal. But old iron comes off quickly, and an overlay leaves any problems in the old underlay and framing under your new roof, where they’re harder to fix later.
How long does a roof tear-off typically take?
Most Waikato homes are stripped and re-roofed in 2–4 days on site. Rain, two storeys or rotten timber can add time. Roofers strip only what they can close in again the same day.
What happens if there’s damage found during a tear-off?
Soft or split battens and purlins are replaced before the new roof goes on. A good quote says how that extra work is priced, and whether you approve it first.
Why do roofers prefer tear-offs?
Because they can see what they’re fixing to. Stripping lets them replace the underlay, check the framing and remove old nails and lead, so the new roof goes on a sound base.
Does a metal re-roof need new underlay?
Yes. NZ Metal Roofing Manufacturers says existing underlay should be replaced, and recommends no more than a single layer of compliant underlay, laps excluded, because doubling up can trap water vapour in the roof space.
Sources: NZMRM Bulletin BU01: underlay on a re-roof · Code of Practice: pre-installation · fasteners · nails · underlay · cutting · swarf · completion · working at height · Dimond: re-roofing steps · NZQA unit standard 30027 · WorkSafe: asbestos
Related: Metal roof replacement in Hamilton · What a re-roof costs · Corrugated iron roofs · The biggest problem with metal roofs
Written by Corey and the CTR Roofing team, Hamilton. Updated November 2026.
