Every roofer on this shelf asks you to ring for a price, or prints a rate per square metre that ignores tear off, scaffolding, waste and the shape of your roof. Both are ways of not answering. Drag the pitch above and watch the two numbers separate: that gap is the first thing a rate per square metre gets wrong, and it is not the largest.
A rate per square metre
146.5 m2 of roof at 58 a metre. This is the number a quote box gives you.
What the job invoices
The same roof with tear off, an 12 percent complexity uplift, scaffolding, waste removal and contingency.
Missing from the first figure
Sixty per cent. Not a rough guide that came out low: a different quantity.
Every figure on this page is produced by the estimator, at its own defaults. Change any of them and all three move.
Not one of these is optional and not one of them is in a rate per square metre. Each column is added to the one before it, so the last column is the price. The short bar underneath is where a rate per square metre stops.
Materials and labour
8,497
146.5 m2 at 58
Tear off
1,611
the old roof has to go somewhere
Complexity
1,213
hips, valleys, dormers, chimneys
Site costs
1,270
scaffolding and the skip
Contingency
1,007
what the felt hides until day two
Invoiced
the number you agree to
a rate per square metre reaches 8,497
The bar is drawn to scale: 62.5 per cent of the invoice. The missing 37.5 per cent is the five columns a rate per square metre does not have.
Put your own roof through it
Pitch is not a style choice. Below the minimum for a material, water finds its way under it, and that is why a low extension roof costs more per square metre than the main house does.
Plain clay tile
Min pitch
35 deg
Rate / m2
58
Years
60 yr
Cheap per square metre and heavy. A roof that has carried concrete for forty years may need its timbers checked before clay goes back on, and that check is in nobody’s rate per square metre.
Natural slate
Min pitch
25 deg
Rate / m2
96
Years
100 yr
The dearest rate on this list and the only hundred-year one. Priced per year of roof it is the cheapest thing here, which is the arithmetic a quote never shows you.
Concrete interlocking
Min pitch
18 deg
Rate / m2
42
Years
50 yr
The default, and the heaviest. Large format means fewer units and faster laying, so the labour line falls even though the material line does not.
Standing seam zinc
Min pitch
5 deg
Rate / m2
132
Years
80 yr
Goes down to five degrees, which is why it turns up over extensions where nothing else works. Almost all of the price is labour, so a complexity uplift bites harder here than anywhere else on this list.
EPDM single ply
Min pitch
1 deg
Rate / m2
68
Years
30 yr
A flat roof is the one case where footprint and roof area are the same number, so every square metre you measure is a square metre you pay for.
The left figure is what a rate per square metre would have told the customer. The right figure is what the job invoiced. Every one of these was produced by the same estimator on this site, at the inputs each job actually had.
Semi-detached, full strip and reroof
Victorian terrace, three bedrooms
Rate only
7,269
Invoiced
11,349
Days
7
Natural slate, hipped roof with two dormers
1930s detached
Rate only
15,297
Invoiced
26,571
Days
14
Concrete interlocking, single storey extension
Rear extension
Rate only
1,576
Invoiced
2,331
Days
3
Standing seam zinc, low pitch over a garden room
New build, garden room
Rate only
5,740
Invoiced
7,828
Days
6
EPDM single ply, flat roof replacement
Garage and utility
Rate only
3,946
Invoiced
5,657
Days
4
Paying cash and paying monthly are not the same job at two prices. They are the same job at one price, plus a second and separate cost: the cost of borrowing. A finance banner leads with the smaller number and stops there, which is the trick a car advertisement runs. Both numbers are below, and the estimator prints them side by side on every job.
Cash price
What the job costs.
The banner figure
60 months at 9.9 per cent APR.
What you repay
288.25 a month, sixty times.
The cost of borrowing
27.2 per cent on top, on its own line.
Everything on this site is an estimate built from numbers you typed. What it cannot see is your roof: the state of the battens, whether the felt has gone, what is under the ridge, and whether the last person to work on it did it properly. Two hours on a ladder settles all four.