Flat & low pitch
Flat roof waterproofing is the design and installation of a continuous membrane over a deck, with falls that actually drain, insulation above the deck, and detailed junctions at every upstand, parapet and outlet. Flat roofs do not fail in the middle — they fail at those junctions. They fail at upstands, at outlets, at the junction with a parapet, and wherever standing water sat because the falls were wrong. Membranes have improved enormously; detailing has not, because detailing is labour and labour is where quotes get cut. We price the detailing explicitly so it does not quietly disappear.
Published benchmark
Quoted per project
Flat roof pricing varies more by build-up and detailing complexity than by area, so a per-m² band would be misleading. We price from the survey.
A cold flat roof — insulation below the deck, ventilated void above — is very difficult to build reliably and is the source of a large share of flat roof condensation failures. Where the structure allows, we build warm: insulation above the deck, vapour control layer below it, no cold void to condense in. It is the more robust construction and it is what we specify unless there is a reason not to.
Water that cannot leave sits, and everything sitting water touches degrades faster — membrane, laps, sealants, upstand terminations. Where the deck cannot be re-laid we build the falls into tapered insulation, set out from the outlet positions rather than applied as a nominal slope.
Southern Italian flat roofs are a heat and UV problem; alpine Austrian ones are a snow load and freeze-thaw problem; Slovenian coastal ones face the bora. Manufacturers themselves segment their systems this way. The right membrane in Bari is the wrong membrane in Salzburg, and we specify by location rather than by habit.
Discuss your roof with us — no sales script, no obligation.
See all questionsA properly built warm-roof build-up with a quality membrane and correct falls should give 25 to 30 years or more. Flat roofs get their bad reputation from cold-roof constructions, nominal falls that leave water standing, and detailing at upstands and outlets that was cut to win the job. The membrane is rarely the problem. The junctions are.
Yes. Water that cannot drain accelerates the degradation of everything it touches — membrane surface, laps, sealants and upstand terminations — and adds load the deck may not have been designed for. Where the deck cannot be re-laid, we build the falls into tapered insulation set out from the outlet positions. A "nominal fall" that ponds is not a fall.
If the structure supports the saturated load, yes — and a saturated extensive build-up is far heavier than the dry figure people quote. It needs a root-resistant membrane, a properly designed drainage and retention layer, and accessible outlets that will actually be maintained. We check the structural case first and are straightforward when the answer is no.
A full reroof on a fixed scope, a fixed price and dates confirmed in writing.
Learn moreAbove-rafter insulation designed to a calculated U-value, installed while the roof is open.
Learn moreThe structural, waterproofing and electrical interface for PV — built in before the panels exist.
Learn moreA fixed-fee survey, a written condition report with annotated photographs, a realistic remaining service life and a costed action list. Credited in full against your project if you go ahead — and still useful if you do not.
Water coming in right now? Mark the enquiry urgent or write to hello@roofpruf.com, and stay off the roof — do what is safe from inside while we read it.