The short answer: some jobs do and many do not, and the deciding factor is almost never the height of the building. What decides it is how people and material get up there, how many days they are on it, and what the perimeter offers by way of protection.
What actually decides it?
Three things, weighed together: the route onto the roof, the duration of the work, and whether the perimeter offers any protection of its own. A low roof reached from a flat rear extension, worked on for an afternoon, behind an existing parapet, is a very different proposition from the same roof reached only from a garden and stripped over several days.
Duration matters more than people assume. A short diagnostic visit and a full re-covering involve the same roof, but one has somebody stepping onto it briefly and the other has crews, rolls, boards and waste moving across the edge repeatedly for days.
When is a ladder and edge protection enough?
When the roof is genuinely low, the ladder can stand on firm level ground you control, and the working edges can be protected without building a structure. On a great many single-storey rear roofs and outbuildings that is exactly the situation, and pretending otherwise would add cost to a job that does not need it.
A garage is the clearest case of all, which is why that type of roof is cheaper to work on than its area suggests. The saving is real, and garages are among the rare jobs where the cheapest way of working is also the right one.
When does scaffold become unavoidable?
When the roof cannot be safely reached or worked from anything less, which in practice means one of a short list of situations. Any of them is enough on its own.
- The roof is at second storey or above, or built into a slope so one side is much higher than it looks
- There is no firm, level, controlled ground to stand a ladder on
- The perimeter is open, with no parapet or wall, and people are working near it for days
- Materials or waste have to be moved in volume rather than carried up by hand
- The work includes the edge itself, so the very thing that would protect people is being rebuilt
- The public or building users pass beneath, and something has to protect them rather than the workers
That last one is easy to overlook and often the real reason. Scaffold on a commercial or residential block is frequently there to keep people underneath safe from what is happening above, not to help anybody climb.
Who arranges it, and whose responsibility is it?
Normally the roofing contractor arranges it through a scaffolding firm and it appears in the roofing quotation, because the contractor knows what the work needs and when. It stays specialist work: it is designed, erected and inspected by people who do only that, and it is signed off before anybody uses it.
Where a client, a main contractor or a managing agent already has scaffold in place for other works, using it is often sensible and always worth raising early. What has to be settled in writing either way is who is responsible for it, how long it stands, whether it suits this roof rather than the last job, and who is paying for the time between it going up and coming down.
Why does it appear as its own line?
Because it is bought separately, it is priced by somebody else, and its cost tracks time rather than roofing. Burying it inside a rate per square metre would hide the one item on the quotation that changes if the programme slips or the design changes.
Shown separately, it also stays checkable. You can see what access has been allowed for, ask what it covers, and understand why a delay costs money even when nobody is on the roof. That transparency is the point of the line, and it is worth reading it as information rather than as padding.
Is a quotation without scaffold cheaper?
Only on paper, and usually only until the work starts. If a roof genuinely needs it, a quotation that omits it has either assumed access somebody has not yet agreed to, or is carrying the item unstated with the intention of raising it once the job is under way. Neither is a lower price; both are a later conversation.
So the useful comparison between quotations is not the totals but what each has assumed about access, which is one of the questions worth putting to anybody before choosing. A survey report settles it before the tendering starts, because access is one of the things a surveyor is standing there looking at.