Flat Roofing In Dartford
Is the roof over your extension holding water again?
EPDM, GRP and felt flat roofs for rear extensions, dormers, bays and porches
Flat roofing in Dartford is mostly small roofs doing hard jobs. A single-storey kitchen extension on the back of a terrace. A box dormer added during a loft conversion. The roof over a bay window, or a porch. They take water off a much larger pitched roof above them, they get stood on whenever someone cleans the upstairs windows, and they're often the first part of a house to leak. Most of the failures we find are at the edges: where the flat roof meets the house wall, around the outlet, or at a split trim. We fit EPDM rubber, GRP fibreglass and torch-on felt. We'll tell you which one actually suits your roof, rather than whichever is quickest for us to lay.
Get a flat roof quote
A roofer rings you back to arrange a visit.
Why it pays to get a flat roof right the first time
A flat roof done badly is back on your list within five years. Done properly, it's a job you forget about. The difference is mostly in preparation and edges.
01
The deck is checked, not just the surface
A new membrane over soft, sagging boards fails fast. We lift the old covering, walk the deck and replace any rotten or delaminated boards with OSB3 or exterior ply before anything new goes down. You see photos of the deck too.
02
A proper fall
Flat roofs shouldn't be truly flat. They need a slight slope so water heads for the gutter instead of sitting in a puddle for a week. Where an old roof has dipped in the middle, we add tapered firrings to put the fall back.
03
Upstands that keep water out
Most flat roof leaks start where the roof meets a wall. We turn the membrane at least 150mm up the brickwork and cover the top with a flashing set into a cut mortar joint. A bead of mastic on its own isn't a fix.
04
Insulation while it's open
Replace more than half a flat roof and Building Regulations expect the insulation to be upgraded. A warm deck puts the insulation above the boards, so the room underneath stays warmer and the timber stays dry. It's far cheaper to do now than later.
05
Edges you won't notice
You look at a kitchen extension every day, often through bifold doors. GRP gets pre-formed trims, EPDM a clean edge detail, and the gutter is lined up properly. Neither should look like an afterthought when you're sitting in the garden.
06
Specified for how you use it
A roof you climb onto to clean a window needs a tougher finish than one nobody touches. A dormer needs different detailing to a porch. We ask how the roof gets used, then choose the system and finish to suit.
1,000+
Roofs repaired, renewed and rebuilt
10 yrs
Written guarantee on every re-roof
5★
The only rating anyone has left us
£0
For the survey and the written quote
Where Dartford houses keep their flat roofs
Walk down a terraced street in Dartford and look over the back fences. A lot of houses have a single-storey rear extension, and many of those have a flat roof that has been re-covered once or twice since it was built. Add box dormers from loft conversions and the little roofs over bay windows and porches, and most homes in town have at least one flat roof somewhere. Because they're out of sight, they tend to be ignored until a stain appears on the kitchen ceiling.
Dry weather helps less than you'd think. North Kent gets far less rain than the UK average, but a flat roof isn't troubled by volume. What wears it out is water ponding for days in a dip, summer sun baking older felt until it cracks, and movement where the extension meets the house. A south-facing extension roof that bakes in July and freezes in January takes a lot of punishment, and any membrane past its best will show it at the seams first.
"Most of the flat roof leaks we get called out to in Dartford start at the wall flashing or the outlet, not in the open middle of the membrane."
How we replace a flat roof in Dartford
- 1
Check above and below
We look at the surface, the edges and the wall joint, then at the ceiling underneath. Soft spots underfoot tell us the deck has taken water. We measure up and note exactly where the water drains off.
- 2
Recommend a system in writing
The quote names the membrane, the deck, the insulation and the edge detail, with VAT included. If EPDM, GRP and felt would all work on your roof, we set out the trade-offs and let you choose.
- 3
Access and protection
Most flat roofs are reached from a tower or ladder. We sheet over the patio, protect sills and agree where materials can sit. If the roof is above your kitchen, we'll talk about timing so you can still cook.
- 4
Strip back to the joists where needed
The old covering comes off. Sound deck stays, rotten deck goes, and firrings are added if the fall needs restoring. This is the stage that cheap flat roofs skip, and it's why they fail early.
- 5
Lay the new roof
On a warm deck, the vapour control layer and insulation go down first. Then the membrane: EPDM bonded as one sheet, GRP laid in resin and glass matting, or felt torched on in layers. Outlets and upstands are formed as we go.
- 6
Edges and flashings
Trims go on, the wall upstand is capped with a flashing chased into the mortar, and the outlet is sealed to the gutter or hopper. These details decide whether the roof lasts, more than the open area does.
- 7
Water test and clear-up
We pour water down the fall to check it runs off and nothing ponds. Then the old felt, boards and offcuts leave site with us, and you get photos of each stage, including the deck before it was covered.
10
Years' cover on a new roof
1,000+
Roofing jobs finished
Paperwork in your hand on the last day. Not posted out "in due course".
What the 10 year guarantee on a re-roof actually covers
Re-roof a house in Dartford with us and you get 10 years of cover on the workmanship. It's a written document. It has your address on it, lists what was done, and is dated the day the roof is signed off. If water gets in because something was fitted wrong - a batten, a fixing, a lap, a flashing - a roofer comes back and puts it right. You don't pay for that.
Why are we happy to promise ten years? Because of how the roof goes on. Every tile or slate is mechanically fixed to BS 5534, the current British Standard. Ridges and hips are fixed too, not just sat in mortar. A breathable membrane goes down first. Where a roof meets a wall, a chimney or the house next door, it gets proper lead or a tested dry system. Shortcuts there are what make a guarantee expensive, so we don't take them.
Tiles, slates and membranes also carry the maker's own warranty. Those vary by product, and your paperwork tells you which ones apply. If a job is too unusual to guarantee in the normal way, you'll hear that at quote stage.
What makes a good flat roofer in Dartford
They insist on seeing under the old roof
Any roofer can lay a new membrane over an old one, and some will offer to, because it's cheaper and quicker. A good flat roofer won't overlay without checking the deck first. Damp trapped underneath rots the boards and blisters the new surface within a few years. Ask what happens if they find soft boards once the old felt is off, and whether that cost is already in the quote.
They know the system they're fitting
EPDM, GRP and torch-on felt are almost separate trades. Each has its own adhesives, laps, trims and details, and each manufacturer publishes how its product should be installed. Ask which system they fit most and how they handle upstands and outlets. Torch-on needs particular care near timber fascias and eaves, since it's laid with an open flame, so ask how they manage that too.
They talk about falls and drainage
If a flat roofer never mentions the fall, the outlet or where the water ends up, they're thinking about the surface and nothing else. Water that can't get off a roof will find a way in sooner or later. A good quote says how the slope will be achieved, what size the outlet is and how it joins the gutter or downpipe below.
EPDM, GRP, felt or lead?
These are the flat roof systems we fit. Each one has a place. Here's how they compare on the kind of small roof most Dartford houses have.
| Comparison point | EPDM rubber | GRP fibreglass | Torch-on felt | Lead (bays and small roofs) |
|---|---|---|---|---|
| Expected life | Commonly 20 to 40 years | Around 20 to 30+ years | Roughly 15 to 25 years | Many decades if detailed well |
| How it's laid | One bonded sheet, no heat | Resin and glass matting that cures hard | Layers torched on with a gas flame | Dressed sheet, cut to set sizes |
| Foot traffic | Fine for occasional access | Copes well with regular use | Good with a mineral cap sheet | Soft, best not walked on |
| Repairs | Easy to patch with matching rubber | Patchable, colour match is harder | Easy to patch | A job for a skilled leadworker |
| Look | Plain matt black | Smooth, can be coloured | Mineral finish, grey or green | Traditional, weathers to grey |
| Best for | Extensions and simple shapes | Dormers, balconies, fiddly edges | Budget re-covers and larger areas | Bay windows and period porches |
Not every bay needs a membrane
Bay window roofs and small porches are where lead still makes the most sense. It dresses neatly over curves, lasts for decades and looks right on older houses. On a newer porch, GRP gives a crisp finish for less money. Our leadwork page covers bays in more depth.
Got a flat-roofed garage at the bottom of the garden? That's a slightly different job, often involving old asbestos cement sheets that need careful handling, so it has a page of its own.
Garage roof replacement
Flat roof prices in Dartford
Replacing the flat roof on a typical 15m² rear extension usually costs £2,200 to £4,200, depending on the system, the state of the deck and whether insulation is added. Bay and porch roofs are smaller jobs, often £450 to £1,300. A detached garage re-covered in EPDM tends to land between £1,300 and £2,400.
Flat roofing questions we hear in Dartford
Do I need planning permission for a new flat roof in Dartford?
Replacing an existing flat roof with a similar one doesn't need planning permission from Dartford Borough Council. Swapping the flat roof for a pitched one might, because it alters how the house looks. Listed buildings and homes in the Town Centre conservation area need more care, as do the West Hill addresses with Article 4 directions. Building Regulations are separate and can apply if more than half the roof is renewed.
Can you lay a new flat roof over the old one?
Sometimes, but we rarely recommend it. Overlaying only works when the existing roof is dry, well bonded and sitting on a sound deck. Most roofs people ask us to overlay have damp somewhere underneath, and sealing that in just lets the boards keep rotting out of sight. Stripping costs a bit more and tells you exactly what you're building on.
Which lasts longer, EPDM or GRP?
Both should last well over twenty years if they're installed properly, and the quality of installation matters more than the choice between them. EPDM copes well with movement and is simple to patch if something sharp lands on it. GRP is harder underfoot and better around awkward shapes. For a plain rectangle on a rear extension, we often lean towards EPDM.
Why is my flat roof leaking when it's only a few years old?
Usually a detail rather than the membrane itself. The upstand at the wall may be too low, or relying on mastic instead of a flashing. The outlet may never have been sealed properly. The roof may not fall, so water sits and finds the weakest lap. Or the old deck was left in place and has kept rotting. We find out which before suggesting a fix.
Can you replace the flat roof on my dormer?
Yes. Box dormers on loft conversions usually have a small flat roof, and its back edge meets the main pitched roof, which is exactly where water tends to get in. We work from a tower or scaffold, replace the covering and redo the junction with the slates or tiles behind it. The dormer cheeks get checked at the same time.
How many days does a new flat roof take?
A typical rear extension takes two to three days of dry weather. EPDM and felt are fairly forgiving about temperature. GRP resin needs dry conditions and mild temperatures to cure properly, so in winter we keep a close eye on the forecast before booking it in. Your kitchen stays usable throughout, though the stripping day is noisy.
Related: Garage roofs · Leadwork · Roof repairs · Guttering, fascias and soffits
Reviews from Dartford homeowners
Every review left for us so far has been five stars. We're adding them here as they come in.
Reviews only tell you so much anyway. When a roofer comes out to Dartford, ask to see photos of a recent job on a house like yours. A good roofer will have plenty and won't mind you asking.
Puddle on the extension roof?
Send a photo or book a visit. We'll check the deck as well as the surface and give you a written price for the system that suits your roof and how you use it.