Two completely different jobs get called refelting. One is recovering a flat roof with a new bitumen membrane system. The other is replacing the underlay beneath the tiles or slates of a pitched roof, which means stripping the covering off to get at it. They share a word and almost nothing else, and knowing which one you need is the first step to reading a quote.
When a flat roof felt repair patch is the right answer
A single split, a lifted lap or a blister on an otherwise sound roof is a legitimate repair, and a competent roofer can cut it out and bond in a matching membrane. The test is whether the rest of the covering still has life in it. If the surface is crazed across the whole area, the mineral finish has washed off, or there are splits in several places, patching buys a season and the money is better spent on a recover.
The cost of refelting a roof: what a flat roof recover involves
Stripping the old layers, inspecting and repairing the deck, correcting or improving the falls, upgrading the insulation where the regulations require it on renovation, then laying the new system in its full number of layers with new trims and outlets. The membrane is a modest part of that. Most of the variation between quotes is how honest each one is about the deck and the falls.
3 layer felt roof cost per m2: why three layers is not marketing
A traditional built up roof gets its reliability from layering: an underlay, an intermediate layer and a cap sheet, bonded and staggered so no joint lines up with the one below. A two layer system is a legitimate specification in the right place. What you want to avoid is paying for a three layer price and receiving a single torched cap over an old surface, so ask for the layer count and the product names.
Refelting under tiles on a pitched roof is a re roof
Replacing the underlay on a pitched roof means taking the tiles or slates off, usually renewing the battens, fitting the new underlay, and re laying or replacing the covering. It is scaffolded work over several days. People often reach it after finding torn bitumen underlay in the loft, and it is worth being clear that this is a re roof with a different name, not a repair.
Access is part of the price
Roof work is the biggest single source of fatal falls in construction and the HSE treats access as part of the work rather than an optional extra. A quote that does not name a tower, a scaffold or an edge protection arrangement has either not costed it or is not planning to use it, and both are worth knowing before you compare prices.
Questions people ask about felt roof repair
Can you felt over an existing felt roof?
It is done, and on a sound roof with good falls it can be defensible with the right overlay specification. It also hides the deck and does nothing about ponding, so ask the contractor to justify it rather than accepting it as the cheaper option.
Why does my flat roof keep blistering?
Blisters usually mean moisture trapped between layers or beneath the membrane, turning to vapour in the sun. Recurrent blistering after repairs points at a wet deck or trapped moisture in the build up, which patching will not solve.
Do I need approval to recover a flat roof?
Replacing a significant proportion of a roof covering is normally notifiable and triggers a thermal requirement for the renovated element. Some contractors can self certify under a competent person scheme, otherwise building control is involved.
How long should a felt roof repair last?
A properly bonded patch on a sound roof should last as long as the surrounding covering. If a repair fails within a season, the diagnosis was wrong rather than the patch, which usually means water is entering somewhere other than where it appeared.