How to estimate a roof replacement (re-roofing quote)
A re-roofing quote starts with roof area, not floor area — you measure the building’s plan (footprint) area and multiply it by a pitch factor to account for slope, then price the job as a stack of separate line items: strip-off and disposal, battens and sarking, the new roofing material, flashings and guttering measured in lineal metres, access and scaffolding, an asbestos allowance where relevant, and a weather contingency. Getting the area and pitch right first means every rate that follows — labour, material, waste disposal — is applied to a number you can defend, not a guess.
Key takeaways
- Roof area equals plan area multiplied by a pitch factor — this single number underpins every other line item in the quote.
- Price the job as separate trades: removal and disposal, battens and sarking, new roofing, flashings and gutters (lineal), access and scaffolding, asbestos allowance, weather contingency.
- Colorbond and tile carry different labour and material rates per square metre — keep both in your rates library rather than using one blended figure.
- Older roofs may contain asbestos cement sheeting — this needs its own provisional line item and must be removed by a licensed asbestos removalist under work health and safety law, not priced as routine demolition.
- My Trade Hub’s roof-area takeoff and editable rates library turn a measured roof into a priced quote up to 60–75% faster than measuring and pricing by hand.
How to measure a roof for a re-roofing quote
You measure a roof by taking the building’s plan area — the footprint you’d get from looking straight down at the roof — and multiplying it by a pitch factor that accounts for the slope, because a sloped roof always covers more actual surface area than the ground beneath it.
The plan area comes from the roof plan if one exists, or from measuring the building perimeter and any eaves overhang on site. The pitch factor is a simple multiplier derived from the roof angle: the steeper the pitch, the bigger the multiplier, and the more material and labour the job needs for the same footprint.
- 0° (flat) — pitch factor 1.00
- 10° — pitch factor approximately 1.02
- 15° — pitch factor approximately 1.04
- 22.5° — pitch factor approximately 1.08
- 30° — pitch factor approximately 1.15
- 35° — pitch factor approximately 1.22
- 45° — pitch factor approximately 1.41
Removing and disposing of the existing roof
Strip-off is priced against the same roof area you just measured, but disposal is its own line item — tip fees and skip bin hire are usually charged by weight or volume, and old tile roofs generate far more waste mass than old metal roofs for the same footprint.
Whether the existing roof is sheet metal or tile changes the removal labour rate too: metal sheets come off in large pieces reasonably quickly, while tiles are removed and handled individually, which adds time. Some jobs skip strip-off entirely by over-roofing (fixing new metal over the old roof) — that avoids disposal cost but should only be priced once the existing structure and sarking have been checked, since problems underneath stay hidden.
- Skip bin or tip fees, priced separately from labour
- Sheet vs tile removal — different labour rates per square metre
- Temporary tarping or weatherproofing while the roof is open
- Over-roofing as an alternative to full strip-off, where the structure allows it
Battens, sarking and re-decking before the new roof goes on
Once the old roofing is off, the frame gets inspected before anything new is fixed — rotten or undersized battens and purlins are replaced, and most Colorbond installs now require a sarking or reflective foil/insulation blanket layer under the code, which wasn’t always present on older tile roofs.
Converting from tile to metal, or metal to tile, can also mean re-decking or adjusting batten spacing, since the two roofing types are fixed differently. This step is best priced as an allowance-plus-rate item: a base battening rate per square metre, with a separate allowance for frame repairs confirmed once the roof is open.
- Replace rotten or undersized battens and purlins
- Add sarking or reflective foil/insulation blanket where required
- Adjust batten spacing or re-deck when changing roofing type
- Keep a separate frame-repair allowance rather than folding it into the batten rate
Colorbond (metal) vs tile — and how it changes your rate
Colorbond and other metal roofing are generally quicker to fix per square metre — wide sheets cover more area per fixing pass — while tile roofing is fixed piece by piece and is more labour-intensive for the same footprint, even though the tiles themselves may cost less per unit than a metal sheet.
Because labour and material behave differently by roofing type, it’s worth holding a separate rate for each in your rates library rather than one blended “roofing” rate — that way a quote for a Colorbond re-roof and a quote for a tile re-roof on the same footprint come out genuinely different, instead of both using an average that’s wrong for both.
The worked example below shows how a re-roofing quote comes together as a stack of line items rather than a single lump sum. Every rate and total in it is an illustrative example only — your own job will use the rates in your own rates library, priced against the specific site.
| Line item | Quantity | Example rate | Example line total |
|---|---|---|---|
| Roof area takeoff & pitch measure | 150 m² | Included in quote prep | — |
| Remove & dispose existing tile roof | 150 m² | $18/m² (example) | $2,700 (example) |
| Battens, sarking & minor frame repairs | 150 m² | $14/m² (example) | $2,100 (example) |
| Supply & install Colorbond roofing | 150 m² | $55/m² (example) | $8,250 (example) |
| Ridge, flashings & valleys | 38 lin m | $32/lin m (example) | $1,216 (example) |
| Gutters & downpipes | 42 lin m | $28/lin m (example) | $1,176 (example) |
| Access, scaffolding & edge protection | 1 job | $1,800 (example) | $1,800 (example) |
| Asbestos allowance (provisional, if applicable) | 1 job | $1,200 (example) | $1,200 (example) |
| Weather contingency | 5% of works | — | $900 (example) |
| Indicative total (example only, not a real quote) | $19,342 (example) |
Ridge, flashings, valleys, gutters and downpipes
These items are priced in lineal metres, not square metres, because they follow edges and junctions rather than covering an area. Ridge capping and barge flashing run along the top and sides of the roof; valley flashing sits where two roof planes meet and carries more water than any other part of the roof, so it’s worth its own line item rather than being buried inside the general roofing rate.
Gutters and downpipes are usually priced separately again — gutters by lineal metre (quad, half-round or box profile), and downpipes counted individually, since the number of drops and their height affects fixings and labour more than length does.
- Ridge capping and barge flashing — lineal metre rate
- Valley flashing — highest water flow on the roof, priced as its own item
- Gutters — quad, half-round or box profile, by lineal metre
- Downpipes — counted by drop, not by length, since fixings drive the labour
Access, scaffolding and edge protection
Access is one of the most under-quoted parts of a re-roof. Work health and safety requirements call for fall protection whenever work is carried out at height, so scaffolding, edge protection or safety mesh and anchor points are a compliance requirement, not an optional extra — and they need their own line item rather than being absorbed into the roofing rate.
Scaffold hire is usually priced by lineal metre of perimeter or by week, and cost climbs with roof height, steeper pitches, and difficult site access such as narrow side access or a tight boundary. Two quotes for the same roof area can differ significantly once access is factored in properly.
- Fall protection is a compliance requirement above the relevant height threshold
- Scaffold hire — priced by lineal metre of perimeter or by week
- Roof height and pitch both push scaffolding cost up
- Difficult site access (narrow side access, tight boundaries) adds time and cost
Asbestos allowance and weather contingency
Homes re-roofed before the mid-1980s to early 1990s may still have fibre cement (AC) sheeting that contains asbestos. At quote stage this is best flagged as a provisional allowance rather than a firm price, because the real cost depends on the condition and quantity of material confirmed once the roof is opened up.
The roof structure is also exposed to weather for the period between strip-off and the new roof going on, so a weather contingency — typically expressed as a percentage of the works rather than a fixed figure — covers tarping, minor rework and delay days without needing to guess a dollar amount up front.
- Treat asbestos removal as a provisional allowance, confirmed on site
- Licensed removalist required by law — never priced as standard demolition labour
- Weather contingency as a percentage of total works, scaling with job size
Asbestos removal is licensed work
Removing and disposing of asbestos-containing material is regulated under work health and safety and asbestos removal laws in every Australian state and territory, and must be carried out by a licensed asbestos removalist. This is general information for quoting purposes only, not legal or trade advice — always have suspected asbestos material assessed by a qualified, licensed professional before any work starts.
How My Trade Hub speeds up a re-roofing quote
My Trade Hub turns the measuring and pricing steps above into one workflow: upload the roof plan and the automated quantity takeoff measures the plan area and roof geometry for you, instead of you scaling a PDF by hand or walking a ladder with a tape measure.
From there, your editable rates library holds your own rates for every line item in this guide — Colorbond and tile priced separately, lineal rates for flashings and gutters, an access/scaffolding allowance, and an asbestos provisional sum — applied automatically to the measured quantities to build a bill of quantities and a client-ready quote.
Because the measuring and rate application happen together instead of in a spreadsheet, verified customer data shows a priced tender or quote comes together 60–75% faster than doing it manually — and every rate stays fully editable, so the quote is built on your numbers, not a generic average.
- Automated roof-area takeoff from uploaded plans, including pitch
- Editable rates library — Colorbond, tile, flashings and access rates, all in AUD, all yours to change
- Bill of quantities and quote generated from the same measured data
- Priced tenders prepared 60–75% faster than manual measuring and spreadsheets
Frequently asked questions
How do I estimate the area of a roof for a quote?
Measure the building’s plan (footprint) area from the roof plan or on site, then multiply it by a pitch factor for the roof’s slope — a flat roof uses a factor of 1.00, while steeper pitches use progressively larger multipliers, since a sloped roof always covers more actual area than its footprint.
What is a roof pitch factor and how do I use it?
A pitch factor is a multiplier applied to the plan area of a roof to account for its slope. You measure the roof pitch (in degrees), look up or calculate the corresponding factor, and multiply it by the plan area to get the true roof surface area used for pricing materials and labour.
How much does it cost to replace a roof in Australia?
There’s no single figure, because cost depends on roof area and pitch, roofing material (Colorbond vs tile), removal and disposal of the old roof, access and scaffolding, and whether an asbestos allowance applies. The most reliable approach is to price each of these as its own line item using your own rates, rather than relying on a generic total — see My Trade Hub’s pricing page for how plans and rates work.
Is Colorbond cheaper to install than tile?
Colorbond and other metal roofing are generally faster to fix per square metre because wide sheets cover more area per fixing pass, while tile is fixed piece by piece and is more labour-intensive for the same area. Material and labour rates for each should be kept separate in your rates library rather than blended into one roofing rate.
Do I need scaffolding to replace a roof?
In most cases, yes — work health and safety requirements call for fall protection whenever roof work is carried out at height, so scaffolding, edge protection or safety mesh is typically a compliance requirement rather than an optional extra, and should be priced as its own line item.
What happens if my roof has asbestos sheeting?
Older homes, particularly those re-roofed before the mid-1980s to early 1990s, may have fibre cement sheeting containing asbestos. This should be priced as a provisional allowance at quote stage and must be removed and disposed of by a licensed asbestos removalist under work health and safety law — this is general information, not legal or trade advice.
How can I quote a roof replacement faster?
Automating the roof-area takeoff from your plans and applying your own editable rates to the measured quantities removes most of the manual measuring and spreadsheet work. My Trade Hub customers prepare a priced tender or quote 60–75% faster this way than doing it by hand.
Ready to win more work?
Turn your plans into professional tenders 60–75% faster with My Trade Hub. Plans built around your tendering volume — no lock-in contracts.
Get started free