Twice a year for a domestic flat roof, plus a check after any severe storm. The useful part is which two visits, and what each one has to cover.
The two that matter are early autumn, before the leaf fall, and spring, once the winter has finished. If you only ever do one, do the autumn one. It is the visit that prevents damage rather than the visit that finds it.
Why a flat roof needs looking at more often than a pitched one
Because of how it drains. A pitched roof sheds water off its edge; a flat roof has to push it through a hole.
That is the whole difference, and everything else follows from it.
On a pitched roof, water runs down the slope into a gutter and away. When the gutter blocks, the water overflows over the front edge, down the wall, where you can see it from the pavement. It is a real problem and it causes real damp, but it tells you about itself.
On a flat roof, there is no free edge. Every drop that lands on it has to leave through an outlet, a chute or a parapet gutter. Block that and the water has nowhere else to go, so it rises and sits. There is no overflow down a wall to warn you, because the parapet or the upstand that stops water running off is doing exactly the job it was built for.
A flat roof holding water is also heavier than a flat roof shedding it, it is working every joint and upstand it has, and it is finding out whether the covering was as continuous as everyone hoped. That is why the interval is shorter here than on the pitched roof over the front of the same house.
For a pitched London roof, once a year plus a look after any major storm is the working answer, and our roof care and maintenance service is built around that year. This article is about the flat sections, which are the part that justifies the second visit.
What an inspection should actually cover
Drainage first, then the details, then the field. That order is not arbitrary: it runs from most likely to cause a problem to least.
Drainage. Outlets, gratings, chutes, parapet gutters, hoppers and downpipes. Are they clear, are they the right size for the area, is anything sitting on the roof after rain that should have left it? On a roof behind a parapet this is the single most valuable ten minutes of the year.
The details. Upstands where the roof turns up a wall or parapet. Laps and terminations. Flashings and abutments. The kerbs around rooflights. Door thresholds where a terrace meets a room. Corners and internal angles, which are the hardest geometry on any roof. Flat roofs almost never fail in the middle; they fail where the covering had to stop, turn or be joined.
Anything standing on the roof. Satellite dishes, aerials, air conditioning units, solar frames, handrails, planters, plant. Whatever is fixed down went through the covering to get there, and whatever is loose on the surface can move in wind and abrade it.
The field of the roof. Splits, blisters, crazing, loss of chippings or surface finish, lifted seams. Where water sits, and whether the pattern has changed since the last set of photographs. A pond that has moved or grown means the roof or the deck below it has moved.
Underneath, where you can get to it. From inside a loft or the room below: staining, drips, mould at the wall head, and the smell of damp timber, which arrives before anything visible does.
What the findings mean is a separate question, and one worth separating from the inspection itself. Our guide to flat roof leak diagnosis covers how to tell a covering fault from condensation, plumbing or a parapet, and ponding water on a flat roof covers what standing water actually does over time.
Which two visits, and why the autumn one matters more
Early autumn, before the leaves come down, and spring, once the winter is over. The autumn visit is the one that prevents damage.
Early autumn. The point of this visit is to have the drainage clear before the weather that overloads it. In London that means before the leaf fall rather than during it, because an outlet clogged in October is an outlet that is going to be tested by every storm from then until March. This is also the visit at which flashings, upstands and terminations should be checked, so anything loose is dealt with before the wet season rather than during it.
Spring. The point of this visit is to find out what the winter did. Frost gets into cracks and opens them, wind works on edges and terminations, and the freeze and thaw cycle is hard on anything already brittle. A spring inspection also catches moss and algae growth while it is still light enough to treat easily.
After any severe storm. Not on a schedule, on the weather. Lifted edges, displaced flashing and debris blown into an outlet all happen on one day rather than gradually, and finding them a week later is far cheaper than finding them in February.
When twice a year is not enough
Five situations justify more frequent checking, and four of them are about what is happening around the roof rather than to it.
Heavy tree cover. The most common one in London. A flat roof under mature trees can block its outlets in a single autumn, and one clearance in September is not enough if the drop runs into December. Two autumn visits is normal on those buildings.
Plant or services mounted on the roof. Condenser units, extract fans, solar frames. Every mounting is a penetration through the covering, every unit vibrates, and anybody servicing one is walking on your roof.
Other trades using the roof as a working platform. This is the one owners forget. Aerial installers, window cleaners, boiler engineers and scaffolders all end up on flat roofs, and none of them has to live with the covering afterwards. A check after any trade has been up there is worth more than a check on a date in the diary.
A roof already known to pond. If water stands after every rainfall, the roof is being loaded and tested continuously rather than occasionally, and the interval should shorten to match.
A roof in the last years of its service life. An old covering does not fail gradually and evenly; it holds and then it goes. Once a roof is known to be near the end, inspection stops being maintenance and becomes the thing that tells you when to schedule the refurbishment rather than react to it.
Commercial and managed buildings run to their own logic, driven by the lease, the service charge and the fact that a leak affects tenants rather than the owner. That is a different subject and it has its own article: commercial flat roof maintenance.
What you can check yourself, and what you should not
You can do a genuinely useful check from an upstairs window or from the ground. You should not walk a flat roof of unknown condition.
Safe and worth doing. Look down at the roof from the window above it. You are looking for water standing after rain, debris around the outlet, splits, blisters, lifted edges, plant growth and anything that has moved since last time. Take a photograph every time from the same window: the comparison is worth more than any single look. From inside, check the ceiling below and the loft if there is one.
Not worth doing. Walking out onto a flat roof you do not know. A deck that has been quietly wet for years gives no warning before it gives way, and older coverings become slippery and brittle in ways that are not obvious from a window. This is not a caution about being careful; it is that the information you would gain is not worth the way it can go wrong.
Where the roof genuinely cannot be seen or safely reached, a drone roof inspection gets high resolution images of the whole surface without anyone standing on it, which is the practical answer on a roof behind a parapet or above three storeys.
Why the written record matters more than any single visit
Because one inspection tells you the condition today, and two a year apart tell you the direction of travel.
That distinction is what turns inspection from a chore into a decision-making tool. A pond that is the same size as last spring is a characteristic of the roof. A pond that has grown or moved means something structural has changed. A blister that was there a year ago and is still the same size is being watched. A blister that has doubled is not.
The same applies to a crack in a parapet, a lifted lap, a stain in the loft. None of them mean much on their own, and all of them mean something when you have the previous photograph next to them.
So whoever inspects your roof should leave you with dated photographs and a written note of what was found, what was done and what needs watching. On a managed building that record is also what a service charge account, an insurer or a leaseholder consultation needs behind it. On a house it is what tells you whether you are budgeting for a refurbishment in two years or in seven.
That reporting is part of how our roof care visits work rather than an extra, for exactly this reason: the value of an inspection compounds, and it only compounds if somebody wrote it down.
What an inspection costs
Ours is free where it is part of assessing work we would quote for, which covers most domestic enquiries in South and West London.
Where you want a standalone survey with a proper condition report and no work attached, a drone survey runs at roughly £150 to £350 for most UK houses. That is an indicative market range for context rather than our quote, and a firm price from K & M Roofing Solutions follows a free survey as it does on everything else.
The comparison worth making is not against zero. It is against what a blocked outlet becomes over one winter: a saturated deck, wet insulation, stained ceilings and a roof that has gone from a repair to a replacement while nobody was looking at it. Our guide to flat roof repair or replacement sets out where that line falls, and the point of inspecting twice a year is to stay on the right side of it.