Best Drone for Roof Inspections: What I’d Fly Over My Own House

Every drone listing shouts a megapixel number at you, and the number is nearly useless on its own. A hundred megapixels spread over an entire terrace is a worse picture of one slate than twelve megapixels aimed at one slate. What you need instead is a single figure that surveyors have used for decades: ground sample distance, or GSD.

GSD is how much real roof one pixel covers. If your GSD is 2 mm, then every pixel in the photograph is a 2 mm square of tile, and nothing narrower than 2 mm can exist in the picture as anything but a smudge. It is the honest ceiling on what the flight can tell you, and you can work it out before you leave the house.

The sum, in full

You need three numbers, and manufacturers publish all three. The 35 mm-equivalent focal length of the lens, the width of the photograph in pixels, and how far you intend to be from the roof.

The 34.6 is the only part that needs explaining. A “24 mm equivalent” lens is defined against a full-frame camera whose diagonal is 43.3 mm; on the 4:3 shape that nearly every drone shoots, that diagonal corresponds to a frame 34.6 mm wide. Drones that shoot 3:2 — the Mavic 4 Pro is the one here — use 36.0 instead.

Put the DJI Mini 5 Pro in: ten metres is 10,000 mm, the lens is a 24 mm equivalent, and the file is 8,192 pixels wide. That gives 10,000 × 34.6 ÷ (24 × 8,192) = 1.76 mm per pixel.

How many pixels does a defect need?

One pixel is not enough. A feature one pixel wide might be a crack, might be a dark lichen streak, might be sensor noise. My working rule — and it is a rule of thumb rather than a standard — is three pixels across the narrowest thing you have to identify. One pixel tells you something is there. Three tells you what it is.

So the question becomes: how wide is the thing you are hunting?

Now run every drone in the guide through the sum, at a sensible ten-metre standoff, and the picture that emerges is not the one the price list suggests.

Three things fall out of that table, and the first one cost me an assumption.

One. The sensor size barely matters here. The £295 Flip and the £689 Mini 5 Pro land 1.79 mm and 1.76 mm apart — a difference of under two per cent, which is nothing. Resolution is decided by how many pixels you spread across the frame and how wide the frame is, and both of those drones spread roughly eight thousand pixels across a 24 mm view. The one-inch sensor buys you a picture that holds together in the shadow under a north-facing eave on a grey December afternoon. It does not buy you finer detail.

Two. A long lens is worth more than any sensor. The Air 3S has a second camera at 70 mm, and that single fact takes it from 1.76 mm per pixel to 0.61 mm at the same distance. Read that the other way round, because it is the point of this whole article: to get the same picture, you can be three times further away from the building. The Mavic 4 Pro’s 168 mm lens takes it to seven times further. A telephoto is not a luxury on an inspection drone. It is a safety feature that happens to also be a lens.

Three. Nothing under 250 grams identifies a hairline crack. To reach 0.33 mm per pixel, a Mini 5 Pro would have to be 1.9 metres from the slate. I have flown that drone a great deal and I would not fly it at 1.9 metres from a building on purpose, on a still day, with nothing to hit. On a real roof, with a gust rolling over the ridge and a television aerial in the frame, it is simply not a thing to do.

That is the honest ceiling on a sub-250-gram roof inspection. You will see missing tiles, slipped tiles, lifted ridges, moss, blocked valleys, failed pointing, daylight through a hole, debris in a gutter and a slate that has gone. You will not reliably see a hairline crack, and any guide telling you otherwise has not done the arithmetic.

One more thing the maths hands you free: the crop is real. If your GSD at ten metres is 1.76 mm, then cropping into a quarter of the frame does not change it. People assume zooming in afterwards costs them detail; it does not, as long as you are looking at actual pixels. What costs you detail is digital zoom in the air, which throws pixels away before they reach the card. Shoot the widest, biggest file the drone offers and crop at your desk.

Suppose the quiz left you with the Mini 5 Pro, as it does for most people who answer honestly about a house in a street. The number in your head is £689. Here is what actually leaves the account before you have taken one useful photograph.

Twenty-seven per cent over the sticker, and I have been conservative — no bag, no spare propellers, no DJI Care. Note what is not on that list: insurance, because for your own house it is genuinely optional. You remain liable for anything you break, but nobody requires a policy.

Doing it for money adds three lines that are not optional. Third-party insurance compliant with Assimilated Regulation (EU) 785/2004, at low-to-mid hundreds a year for the £1 million cover clients ask for. An Operator ID registered in the trading name rather than yours. And the data-controller duties that come with holding photographs of other people’s property. None of that is difficult; all of it is the difference between a hobby and a business, and skipping it is not a grey area.

The case for not buying anything

Here is the arithmetic nobody selling drones will do for you. If you have one roof and one question, you are about to spend £878 and a fortnight of learning to fly in order to answer it — and at the end you will have a sub-250-gram drone that, as Part Three showed, cannot resolve a hairline crack and has no thermal camera at all.

Thermal is the part that stings. Trapped moisture changes how a roof gives up heat, which is why a survey with a thermal camera can show you where water is getting in before anything visible has failed. The camera that does it — the 640×512 sensor on a Mavic 3T — is not sold in shops at any price you would consider. A drone roof inspection booked from a pilot who already owns one arrives with the drone, the qualifications, the insurance and that sensor, on a day when the weather suits it.

I am not going to quote you a price for that, because it moves with access, airspace, the size of the building and whether you need a thermal pass or a full three-dimensional model. What I will say plainly is this: for one roof, once, hiring is almost always the cheaper answer, and it is the answer I would give a friend. Buying starts to make sense at the point where you will be doing this repeatedly — a landlord with a portfolio, a roofer who quotes twenty jobs a year, a surveyor tired of ladders.

So: what I’d fly over my own house

The DJI Mini 5 Pro, at £689, and I would not agonise over it.

Not because of the one-inch sensor — Part Three demolished that as a resolution argument. I would buy it because it is the only drone here that combines three things a roof demands at once: obstacle sensing in every direction with a laser to back it up, eyes that keep working down to 1 lux in the shade where the damage hides, and a take-off weight of 249.9 grams, which means I may fly it over a residential street with nothing but the £12.34 registration. On a terrace or a semi, that last point is not a convenience. It is the difference between a legal flight and an illegal one.

Spend less if the roof is detached. The DJI Flip at £295 puts the same 1.8 mm per pixel on your tiles and comes in propeller cages, which is the drone I would hand somebody who has never flown. It watches forwards and downwards and nothing else, so give it open air on three sides and it will do the job for four hundred pounds less.

Spend more only for the second lens. The DJI Air 3S at £959 is the one I would buy if I were inspecting roofs for other people. Its 70 mm camera means the same detail from three times the distance, and that is the single best safety-and-quality trade on this page. Go in knowing it is 724 grams, so you may not fly it over anybody, and that its no-qualification status expires in January 2028.

The one I’d actively tell you not to buy for this

The DJI Neo, at £119 — and I say that as someone who genuinely enjoys flying it. It is a delightful object. It is also, for this specific job, a trap dressed as a bargain.

Its 14 mm lens spreads twelve megapixels across an enormous field of view, which puts it at 6.18 mm per pixel from ten metres. To get to the 1.7 mm you need for a mortar joint, you would have to fly it 2.8 metres from the roof — and it has no forward obstacle sensing whatsoever. The cheapest drone on the page asks you to fly closest to the building with the least protection. That is precisely backwards, and it is how people put a drone through a conservatory roof.

If none of this appeals — and for one leak, once, it should not — that is what the rest of this site is for. You can hire a qualified drone pilot who already owns the drone, the certificate and the insurance, and who will hand you a report rather than a memory card.