Pitch changes the quantity, not just the method
A sloped surface is bigger than its shadow on the ground, and the gap grows with the angle. Pricing a pitched roof off a plan area quietly under-orders.
The problem
Nobody prices a roof they have not been on.
An estimator needs area, pitch and height before they can quote, and the only ways to get them are a ladder, a scaffold or a guess off satellite imagery. The first two are a visit and a risk assessment. The third gives a plan outline with no pitch and no height, which is most of what the quote turns on.
Access is the cost before any work happensA ladder on a commercial building is a method statement, a second person and a morning, spent before anybody knows whether the job is worth quoting for.
Satellite imagery flattens the thing you are pricingIt gives you an outline. It does not give you pitch, it does not give you height, and it cannot tell a pitched block from a flat one.
An insurer sets a reserve from the same guessesArea and construction drive the number, and both are usually taken from a file that was accurate when the policy was written.
Why this gets commissioned
A roof is priced on three numbers nobody has.
Area, pitch and height. Together they decide the materials, the access equipment and most of the labour. They are also the three things least likely to be written down anywhere, because getting them has always meant going up.
Height decides the access, which is often the biggest line
Whether a job needs a tower, a scaffold or a cherry picker is settled by a figure most estimates carry as "about".
A survey is proportionate to a job you have already won
Not to one you are bidding for. The measurement everybody needs is the one before the decision, and that is the one nobody pays a surveyor for.
The same three numbers serve four different trades
The roofer, the insurer, the facilities manager and whoever is costing solar all start from area, pitch and height.
What it changes
What it changes.
Area, pitch and height from one routine flight
No ladder, no scaffold, no access equipment and nobody on the roof to get them.
Each face separately, not one average
The two pitched faces came out at 14.9 and 13.5 degrees. A single rounded figure would have hidden that they differ.
Every number carries its margin
Scale comes from the drone’s own positioning rather than ground control, so the figures are a guide of about three to five per cent and the page says so beside them.
It says what it did not read
Half the roof is not explained by the fitted planes and the page publishes that share, because three planes without it would imply the whole roof had been read.
What it is used to decide
The questions it is there to answer.
All of them are decisions a person makes with a better number in front of them, and none is a survey.
Is this job worth quoting for?Area and height before the site visit, so the visit happens for jobs worth having rather than to find out.
What access will it need?A typical roof height of about seven metres above ground is the figure that decides tower against scaffold, and it is read here rather than estimated from the photographs.
How much material, roughly?Plan area by face, with the pitch beside it so the sloped area can be worked out rather than assumed. See the limits below: the figure published is the plan area.
Is the file we hold still right?For an insurer or a facilities manager, comparing a current read against a record written years ago is the cheapest check available.
The readings
What was measured, and how firm each figure is.
Every figure on this page says what kind of figure it is. That is the whole of why it can be used.
3,793 m²roof plan area, or 40,827 sq ftMeasured on the 3D, to about three to five per cent. This is the PLAN area seen from above, not the sloped surface.
6.8 mtypical roof height above groundMeasured, with the same margin. It is the figure that decides the access equipment.
14.9° and 13.5°the two pitched faces, facing NNW and SSEMeasured on the planes themselves: 331 m² and 294 m² of plan area. They are not the same pitch and are not reported as one.
51%of the roof is not explained by any fitted planeMeasured. Plant, upstands, raised sections and surfaces the flight did not resolve cleanly enough to call. Published because three planes without it would read as a complete survey of the roof. The flat section that did fit is 220 m² at half a degree.
292 of 293photos placed in the 3DMeasured. One routine crosshatch flight over one building.
0.96 mmedian fit of those photos to the drone’s own positioningMeasured. It is what the three to five per cent comes from, and it is the thing RTK or ground markers would improve.
Honestly
What this is not.
Plan area, not surface area
The number on this page is the roof’s shadow on the ground. The sloped surface of a pitched face is bigger, and the page gives the pitch so the conversion can be made.
Not a condition report
No damage reading at all. The white metal renders too noisily for it and we are not going to pretend otherwise.
Where a surveyed figure exists, it wins
Three to five per cent is good enough to decide whether to quote and what access to plan for. It is not good enough to settle a boundary, a claim or a contract quantity.
No saving is claimed, because none was measured
Nothing here was compared against a ladder visit or a satellite estimate, so there is no figure for what it saves.
Captured by Airweb’s drone pilot network. The flying is theirs and the reading is ours. Their logo is their own, shown on a dark panel of ours so it is legible here.
Questions we get asked
Before you ask.
Is this a survey?
No. Scale comes from the drone’s own standard positioning rather than from ground control, so every figure is a guide of about three to five per cent. Where a surveyed figure exists, the surveyed figure wins. What this replaces is a guess, not a survey.
Can I order materials off the area?
Not directly, and this is the most important line on the page. The published area is the PLAN area, the roof’s shadow on the ground. The real surface of a pitched face is larger: divide by the cosine of the pitch, which at about fifteen degrees adds roughly three and a half per cent. We did not do that conversion on this job, so we are giving you the plan area and the pitch to do it with rather than a number that looks finished and is not.
What is the 51 per cent?
The part of the roof that did not fit any of the three planes: plant, upstands, raised sections, and areas the flight did not resolve cleanly enough to call. It is on the page because leaving it off would make three planes look like a whole roof.
Does it find damage?
No. The white metal roof renders noisily in the 3D, so reading damage off it would be guesswork, and we would rather say that than sell a condition report nobody should act on. For damage, look at the photographs closely. That is a different job and we would scope it as one.
How would you make it tighter?
RTK, or ground markers. Either takes the scale from metres to centimetres and the figures from a guide to something an engineer can lean on. Neither was used here.
What did you get wrong?
The first attempt at finding ground level picked a lawn rather than the hard standing, which put the roof height out, and it was redone. Everything on this page is from the second pass.
How much does it save?
We do not know and we will not put a figure on it. Nothing on this job was compared against a ladder visit or a satellite estimate, so there is no saving to quote and we are not inventing one.
What does it need from us?
One routine crosshatch flight over the building, flown by pilots who already fly them. No access equipment and nobody on the roof. If you already hold suitable footage we will look at that first.
Got a roof nobody has been on this year?
Tell us what the building is and what you need to know about it. We will say whether this would answer it, including when it would not.