Calculate Roofing Materials (Australia)

What this calculator estimates

This is a full-takeoff calculator for an Australian metal or tile roof in 2026. Enter your roof footprint, pitch, and profile choice and it returns:

1. On-slope roof area — footprint × slope factor, plus your chosen waste %
2. Roof sheets in linear metres — Custom Orb 762 mm cover, Trimdek 762 mm cover, or Klip-Lok 700 mm cover
3. Roof tiles — concrete or terracotta, at the standard 10 tiles per m²
4. Tek screws — 12-14×65 mm with neoprene washer, at AS 1562.1 fixing density
5. Sarking — foil-backed Anticon or Aircell at 1.35 m or 1.5 m roll widths
6. Top-hat battens — 40 mm or 64 mm sections at the spacing your profile demands
7. Ridge cap — 3 lm sticks of matching profile in the same Colorbond colour
8. Barge cap and valley iron — sized to gable rakes and inward planes
9. Gutters and downpipes — to AS/NZS 3500.3 minimum capacity for your roof catchment
10. Material cost estimate in AUD — at 2026 BlueScope Lysaght and tile manufacturer pricing

Step 1 — Measure the footprint in metres

Walk your house and measure length and width to the gutter line, not to the wall. Add the eaves overhang on every side. For an L-shaped or T-shaped house, split into rectangles, calculate each, then add. If you have a build drawing, plan view or council plan, the footprint is on it.

A typical Australian three-bedroom brick veneer is around 12 × 8 m to the gutter line. A four-bedroom volume builder home runs 16 × 12 m. Do not guess from the room sizes — they exclude eaves and verandahs.

Step 2 — Determine the pitch in degrees

Australian roofing convention is degrees, not the X/12 fraction used in the US. Common AU residential pitches:

• 15° — low-slope tin roof, Federation cottage style or modern minimal designs
• 22.5° — minimum allowable for tile under AS 2050, common on hip-and-valley brick veneer
• 25–30° — typical contemporary volume-builder home in Colorbond
• 35° — steep hip roof, often on heritage replicas or larger two-storey homes
• 45°+ — feature pitch on pavilion-style or alpine designs

Use the roof pitch calculator if you need to measure an existing pitch from inside the roof space. The slope factor that converts plan area to on-slope area is:

slope factor = 1 / cos(pitch in degrees)

So a 22.5° roof has slope factor 1.082 — the roof surface is 8.2% larger than the plan footprint. A 35° roof has slope factor 1.221 — 22.1% larger. A 45° roof: 1.414. The steeper the roof, the more material you need for the same house footprint.

Step 3 — Choose your profile and order in lineal metres

Australian metal roofing is sold in lineal metres (lm) of sheet. Each profile has a fixed effective cover width:

• Custom Orb (corrugated) — 762 mm effective cover, 0.42 mm BMT standard, suits 5° minimum pitch
• Trimdek — 762 mm effective cover, 0.42 mm BMT, suits 3° minimum pitch
• Klip-Lok 700 — 700 mm effective cover, concealed-fix clip system, suits 1° minimum pitch
• Spandek — 700 mm cover, similar to Klip-Lok
• Zincalume unpainted — same profiles, different finish, 30–40% cheaper than Colorbond

To convert your on-slope roof area (m²) to lineal metres of sheet:

sheet metres = on-slope area / cover width (in metres)

For Custom Orb that is area / 0.762. For Klip-Lok 700 it is area / 0.700. Order full lengths to match your eave-to-ridge run plus 50 mm overhang into the gutter and a 50 mm overlap at the ridge. Long-length Colorbond ordered factory cut to length wastes less than site-cut sheets.

Step 4 — Tile takeoff

Concrete and terracotta tiles in Australia are sized to a 10-tiles-per-square-metre laid coverage (each tile around 330 × 420 mm with an effective lap). Multiply your on-slope area by 10 to get the tile count, then add waste:

• 5% waste — simple gable roof
• 8–10% waste — hip-and-valley roof with cut tiles at every hip and valley
• Add 50 ridge tiles per ridge stick of 3 m, plus barge tiles to suit

Tiles need sarking under them (AS 4200.1) and timber battens at 320–345 mm centres depending on the tile. Concrete tiles (Monier Wunderlich, Boral) are around 4.5 kg each — confirm your roof framing was designed for tile loading or you will overstress the trusses. Terracotta tiles (Bristile, La Escandella imported) are 3.8–4.2 kg each.

Step 5 — Fixings, sarking and battens

Tek screws — 12-14×65 mm Class 3 or Class 4 galvanised with neoprene washer, sometimes called type 17 self-drilling. AS 1562.1 fixing density: every second crest at sheet ends and side laps, every fourth crest at intermediate battens. Plan on 8 screws/m² for non-cyclonic zones, 10–12/m² for cyclonic regions C and D under AS/NZS 1170.2.

Sarking — Anticon 60 (Fletcher Insulation) or Aircell Permishield (Kingspan) at $3–6/m² supplied. Class A non-combustible required under BAL-FZ.

Top-hat battens — 40 mm steel top hats for tile (320 mm centres) or 64 mm steel top hats for metal (1200 mm max centres). Galvanised steel battens at $5–9/lin m. Timber battens 70×35 mm hardwood are still legal but check with your engineer for cyclonic zones.

Ridge cap, barge cap, valley iron — Lysaght angled ridge in matching Colorbond colour, 3 lm sticks. Valley iron in 2.4 m sticks at every inward roof plane junction.

Step 6 — Set the waste percentage

• 5% — simple gable Colorbond, factory-cut full-length sheets
• 8% — hip roof with four planes meeting at the ridge
• 10–12% — cut-up roof with valleys, dormers, skylights, changes of pitch
• 6% — gable tile roof
• 10% — hip tile roof

Step 7 — Read the results

The calculator returns lineal metres of sheet, screw count, sarking m², batten lineal metres, ridge cap lineal metres, gutter and downpipe runs, and a 2026 AUD cost band. Save the screen for your supplier or roofing contractor.

Worked example — 12 × 8 m hip roof, 22.5°, Colorbond Custom Orb 0.42 mm

Footprint = 12 × 8 = 96 m²
Slope factor = 1 / cos(22.5°) = 1.082
On-slope area = 96 × 1.082 = 103.9 m²
With 8% hip waste = 112.2 m²
Custom Orb sheets = 112.2 / 0.762 = 147.2 lm

Tek screws at 8/m² = 112.2 × 8 = 898 screws
Sarking = 112.2 m² (≈83 lm of 1.35 m roll)
64 mm top hats at 1200 mm centres = approx 87 lm
Ridge cap = 12 lm (one ridge stick + hips)
Valley iron = 4 hips × 5 m approx = 20 lm
Gutter (perimeter) = 2(12+8) = 40 lm
Downpipes = 4 × 90 mm round

At 2026 BlueScope pricing this comes to roughly:

• Custom Orb 0.42 mm × 147.2 lm @ $19–28/lm = $2,800–4,120
• Sarking 112 m² @ $3–6 = $336–672
• Battens 87 lm @ $5–9 = $435–783
• Tek screws 900 @ $0.45–0.85 = $405–765
• Ridge, barge, valley flashings: $400–700
• Quad gutter 40 lm + 4 downpipes: $480–800

Materials supplied total: ~$4,856–7,840. Add labour at $60–95/m² for installation = $6,230–9,860, plus tear-off if reroofing ($35–55/m²). All-up installed roof: $13,000–22,000 for a 12×8 m hip roof in metro Melbourne, Sydney or Brisbane.

Standards and regional considerations

• AS 1562.1:2018 — installation of metal sheet roofing
• AS 2050:2018 — installation of roof tiles
• AS/NZS 1170.2 — wind actions, with cyclonic regions C and D demanding tighter fixing schedules
• NCC 2022 Volume Two — residential building requirements including thermal performance
• AS 3959:2018 — bushfire construction; BAL-12.5, BAL-19, BAL-29, BAL-40, BAL-FZ
• AS/NZS 3500.3 — stormwater, gutters and downpipes sized to catchment

In cyclonic Queensland and northern WA, every fastening, ridge cap and barge has cyclonic-rated detailing. In bushfire-prone areas, sarking, vents and roof-wall junctions must meet the BAL rating — non-combustible Class A products only at BAL-FZ.

Common mistakes

Forgetting the eaves. A 12 × 8 m house with 600 mm eaves all round is a 13.2 × 9.2 m footprint = 121.4 m² before slope factor. People measure to the wall and come up 25 m² short.

Using Custom Orb on a 3° pitch. Below 5° you must use Trimdek or Klip-Lok — Custom Orb leaks in driving rain. Check the Lysaght installation manual for your profile.

Ignoring the cyclonic uplift schedule. Standard 8 screws/m² is fine in Adelaide. In Cairns it must be 10–12/m² with engineered washers. The roofer is liable if a cyclone lifts the roof and the schedule is wrong.

Wrong batten centres for tile. Concrete tiles need 320–345 mm centres. Wider centres bow the tiles and crack them in the first hailstorm.

Skipping sarking. NCC 2022 Section J effectively requires sarking on metal roofs in cool climate zones. Skipping it fails inspection and ruins the thermal envelope.

What this calculator excludes

• Solar PV mounting and pen-flashings — quote separately
• Whirlybirds and ridge venting — sized by attic CFA
• Roof-wall step flashing where the roof meets brickwork
• Skylights and roof windows — sized individually
• Box gutters between two roof planes — designed to AS 3500.3 with overflow

For a complete project budget, add 8–12% to the materials cost for accessories, plus your labour and tear-off line items.

Related calculators

• Roof square footage calculator — converts plan area to on-slope m²
• Roof pitch calculator — find your pitch in degrees first
• Flat roof replacement cost calculator — for low-slope membrane roofs (TPO, EPDM, torch-on)

Sources: AS 1562.1:2018 Metal roofing installation; AS 2050:2018 Installation of roof tiles; AS/NZS 1170.2 Wind actions; NCC 2022 Volume Two; AS 3959:2018 Bushfire construction; AS/NZS 3500.3 Stormwater drainage; BlueScope Lysaght 2026 technical literature and pricelist; Master Builders Australia 2026 contractor cost guide; hipages roofing 2026 quote data; Monier Wunderlich and Bristile Roofing 2026 product specifications.