A flat roof rarely fails with much warning. One wet winter and the felt that has looked fine for years starts to blister, pool water and let damp into the ceiling below. If you are pricing a replacement, this guide sets out what a new flat roof typically costs in the UK, why quotes vary so much, and how to judge whether a figure is fair for a property in Maidstone or the wider Kent area.
Most quotes are worked out per square metre, then adjusted for access, edge details and how much of the old roof has to come off. The material you choose is the biggest single factor. As a rough guide for a full strip and replace, including new decking where needed, these are the ranges we see across Kent in 2026.
For context, a single garage roof is usually 15 to 20 square metres, a rear kitchen extension is often 20 to 35, and a large flat-roofed dormer can be 10 to 15. Very small jobs cost more per square metre because scaffolding, skip hire and labour do not scale down neatly.
Two roofs of the same size can come back with quotes hundreds of pounds apart, and it is usually not the roofer being greedy. The condition of what is underneath matters most. If the old felt has been leaking for a while, the timber deck may be soft and need replacing, which adds material and a day of labour. Rotten joists are rarer but not unusual on older Maidstone terraces and 1960s extensions.
Insulation is the other big variable. Building Regulations in England require a roof to be brought up to a minimum thermal standard when more than half of it is replaced, which normally means adding rigid insulation boards to a warm roof build-up. That can add £30 to £50 per square metre but noticeably cuts heating bills in a room below.
Beyond that, expect the quote to reflect the number of upstands, rooflights, pipes and outlets that need detailing, whether the roof is a first-floor extension needing scaffold or a ground-floor garage reachable from a ladder, and how many layers of old material are already on there. Some roofs in Kent have three generations of felt stacked up, and stripping and disposing of all of it is heavy work.
Some contractors will offer to overlay a new membrane on top of the existing felt for perhaps 30 to 40 percent less than a full replacement. It can be a reasonable option if the deck is dry and sound and the existing roof is a single layer with a decent fall, but it locks in any trapped moisture and adds weight. If there is any sign of ponding, sagging or damp staining inside, a full strip is the safer money.
A related decision is whether to fix the fall. Many older flat roofs in the area were built almost level, which is why water sits on them. Firrings or tapered insulation can be used to create a proper slope during a replacement, and it is far cheaper to do that now than to revisit it later.
A proper written quote should state the material and its thickness or grade, whether the deck is being replaced or inspected and priced separately, what insulation is included, how the edges and any abutting walls are being finished, and who is responsible for skips, scaffold and Building Control notification. If those points are missing, ask for them in writing before you compare prices.
It is also worth asking about the guarantee. Membrane manufacturers typically offer 20 years or more on EPDM and GRP when installed by an approved contractor, and a torch-on felt system is usually guaranteed for 10 to 20 years. Make sure the workmanship guarantee is separate from the product one and is backed by an insurer, not just a promise on the invoice.
A single garage or small extension is usually done in one to two days once materials are on site. Larger roofs, or those needing new decking and insulation, typically take three to five days, and work is generally paused in heavy rain.
Planning permission is rarely needed for a like-for-like replacement. Building Regulations do apply when you replace more than half the roof, mainly for insulation and fire performance, and a competent roofer will either self-certify or arrange the Building Control notification.
Patching a single split or a failed joint can cost £150 to £400 and buys time on a roof that is otherwise sound. Once a felt roof is blistering across large areas or has been leaking for a season, repairs tend to chase the problem around and a replacement usually works out cheaper over five years.
Free quotes across Kent, with straight answers about what the roof actually needs.