Roofing Calculator NZ
Use this free roofing calculator to work out your roof area, materials needed and cost estimate for your project in New Zealand.
How to calculate roofing area in NZ
Your roof area is always larger than your floor plan. The difference depends on your pitch. A 15° pitch adds about 4% more area. A 25° pitch adds around 10%. A 35° pitch adds 22%. The formula is: floor plan area × (1 ÷ cos of pitch angle) × number of roof sides. Add your eaves overhang on all sides, then add 10% waste. That's what you need to order.
The easiest way to get your floor plan area is Google Maps satellite view — trace your roofline using the Measure Distance tool. You get the footprint in m². Run it through the Area tab above to get actual roof area.
NZ roofing cost guide (2025/26)
Material costs vary significantly by type. Longrun Colorsteel is the most popular choice — it runs $80 to $130 per m² fully installed including labour, flashings and ridge caps. Corrugate iron is cheaper at $60 to $110 per m² but requires more joins and has a shorter lifespan. Concrete tiles (Monier) cost $90 to $160 per m² installed and last 50+ years. Clay tiles are the premium option at $130 to $220 per m² but can last 80 to 100 years with minimal maintenance.
For a standard NZ three-bedroom home with around 120 to 150 m² of roof area, expect to pay $12,000 to $30,000 for a full reroof depending on material choice and roof complexity. Steep pitches, multiple valleys, skylights and penetrations all add cost. Always get three quotes from licensed NZ roofing contractors.
Minimum pitch requirements in NZ
Each material has a minimum pitch below which it will leak. Longrun steel — 3°. Corrugate iron — 8°. Concrete tiles — 15°. Clay tiles — 20°. Going below these minimums voids the manufacturer warranty and breaches the NZ Building Code. If your roof is below 8°, longrun steel is your only practical option other than a flat membrane system.
How many screws do I need for metal roofing?
For longrun steel, allow 5 Tek screws per m² as a starting point. On a 120 m² roof that's 600 screws — six boxes of 100. Always use Tek screws with neoprene washers rated for exterior use. Standard zinc screws will corrode within a few years in NZ conditions. For coastal locations use grade 316 stainless steel screws. The Materials tab above estimates screws and boxes automatically.
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Frequently asked questions
How do I calculate how much roofing I need?
Measure your house footprint, multiply by your pitch multiplier (1 ÷ cos of pitch angle), add eaves overhang on all sides, then add 10% waste. Our calculator does this automatically — enter your dimensions in the Area tab.
What is the average cost to reroof a house in NZ?
A full reroof of a standard NZ three-bedroom home costs approximately $15,000 to $35,000 installed. This includes removal of the old roof, new longrun Colorsteel, flashings, ridge caps and labour. Tile reroofs are at the upper end of this range.
What is the average cost per m² for roofing in NZ?
Longrun steel $80–$130/m². Corrugate $60–$110/m². Concrete tiles $90–$160/m². Clay tiles $130–$220/m². These are fully installed prices. Materials-only cost is roughly 30–50% of the installed price.
Can I measure my roof using Google Maps?
Yes. Search your address in Google Maps, switch to satellite view, right-click and select Measure Distance. Trace your roofline to get the floor plan area. You still need to apply a pitch multiplier to get actual roof area — the satellite view shows the flat footprint only. Use the Area tab above to convert it.
What is the minimum pitch for Colorsteel in NZ?
Colorsteel longrun steel requires a minimum 3° pitch. Corrugate iron requires 8°. Below these minimums water backs up under the sheets and leaks occur. Check your pitch before selecting your material.