The cheapest repair is the one done early on the thing that is actually wrong. Every expensive roof repair started as a cheap one that was patched, ignored or misdiagnosed. All the trade figures below are published cost-guide rates that exclude VAT and exclude access equipment.
Fix the defect, not the symptom
Most leaks trace back to a small number of cheap causes: a broken or slipped tile, a failed flashing, a blocked gutter, or storm damage. Dealt with at that stage the work runs £170 to £400. Left across two winters the water reaches the timber, and you are paying for wet rafters, rotted battens and perished underlay at £500 to £1,500 or more.
Sealant and mortar bodges are what turn the first number into the second. They can look like a fix and fail inside two winters, by which point the water has been getting in the whole time.
The order worth working through
Start with the gutters. A blocked or overflowing gutter is one of the commonest causes of what looks like a roof leak, water backing up over the fascia and into the wall or the eaves rather than coming through the covering at all. Clearing it is the cheapest intervention on the roof and it sometimes ends the problem.
Next, slipped or broken slates and tiles. Up to five tiles is £170 with straightforward access, or £225 where a roof ladder is needed and the tiles have to be bedded.
Then flashing. Re-dressing lead runs £50 to £70 per metre for straight Code 5 work and £80 to £120 per metre where it is stepped around a chimney, which is the usual arrangement on a South London terrace.
Access is the swing factor, not the materials
The same five-tile job that costs £170 with straightforward access costs about £500 once a scaffold is required and the tiles are hard to source. Nothing about the tiles changed. The whole difference is how someone gets to them safely.
That has a practical consequence: bundle small jobs. If access equipment is going up anyway, having the gutters cleared, the ridge repointed and a few slates re-bedded at the same visit costs a fraction of three separate call-outs. The cheapest way to fix a leak is often to fix everything else the roof needs while someone is up there.
When a temporary repair is the right answer
There is exactly one situation: water is entering now, and weather or availability stops a proper repair happening this week. A tarpaulin or make-safe at £100 to £400 buys days to weeks, and it is worth every penny of that when the alternative is a saturated ceiling.
It buys days to weeks, not years. A make-safe that is still on the roof next spring has become the repair, and it is not one.
This is not a DIY job
Checkatrade is unambiguous that roof repairs are not suitable DIY projects, and the safety data explains why. Falls from height caused 31 of the 126 worker deaths in Great Britain in 2025/26. A homeowner on a ladder over a wet slate roof is the exact scenario behind those figures, without the planning, training or equipment the Work at Height Regulations 2005 require of anyone doing it for a living.
The saving is also smaller than it looks. A £170 job saves you £170 and costs you the ladder hire.
Insurance covers sudden damage, not wear and tear
Home insurance often covers sudden damage such as a storm or a falling tree, including the emergency make-safe that follows it. It does not cover deterioration. A roof that has been quietly leaking for three years is a maintenance problem, and an insurer will treat it as one.
That is another argument for reporting and fixing early. Storm damage claimed promptly is a different conversation from the same damage found two years later.
Cheap and expensive on a roof leak are separated by how long it took someone competent to look at it.