Which lasts longer, EPDM or GRP?

A single piece EPDM membrane on a sound deck typically gives 25 to 30 years and has no seams to fail on a domestic sized roof. GRP is similar in life and harder wearing underfoot, though it can craze if the deck moves or if it is laid in cold or damp conditions. On a Leeds dormer we usually recommend EPDM. On a balcony that gets walked on, GRP wins.

Why does water sit on my flat roof?

Because the fall is too shallow or the deck has sagged. Flat roofs are never flat. Good practice is to design in a fall of around 1 in 40 so that the finished roof still drains at 1 in 80 after everything has settled. Old felt roofs on Leeds extensions were often laid nearly level, and ponding water is what splits the seams.

Do I need Building Regulations approval for a flat roof?

For a repair, no. For a full strip and recover, yes. The roof counts as a thermal element, so recovering most of it triggers a requirement to upgrade the insulation to current standards where that is feasible. That usually means PIR board in a warm deck build up. We tell you at the survey whether your job crosses the line.

Can you lay a new covering over the old felt?

Sometimes, and it is usually a false economy. If the deck below is wet, the moisture is trapped and it blisters the new membrane within a couple of summers. We only recover in place where the deck probes dry, the fall is right and the extra height works at the threshold. Otherwise we strip it.

What about the dormer cheeks and the upstand?

That is where most dormer roofs leak. The membrane has to carry up behind the cladding or into a chase in the brickwork, with a proper lead or trim detail at the top. We renew the cheeks and the flashing as part of the job rather than dressing the new rubber against old, cracked mortar.

Will the new roof take my ladder and my foot traffic?

EPDM handles normal maintenance traffic fine, and we can add a walkway strip where you regularly access a Velux or an aerial. For a roof that gets used as a terrace or sits under a loft window people climb through, GRP with a non slip topcoat is the more sensible choice. Tell us how the roof gets used at the survey.

Flat Roofing in Leeds: EPDM and GRP

A new EPDM flat roof in Leeds costs £95 to £165 per square metre, so a typical 12 square metre dormer or garage lands between £1,150 and £2,000. GRP costs a little more. Most flat roofs here fail because water sits on them, so we rebuild the fall and move the outlet before choosing a membrane.

Signs you need this

Water still standing on the roof two days after the rain stopped

Blisters or bubbles across old felt that move when you press them

A split along a seam or at the upstand where the roof meets the wall

Green algae and silt marking out a low spot

Ceiling staining in the room below the dormer or the back extension

Chipboard decking that feels soft underfoot at the edges

Where flat roofs turn up in Leeds

Three places, mostly. Rear extensions on 1930s semis in Pudsey, Horsforth and Morley. Box dormers on terraces converted into loft rooms, which is half the student stock around Headingley and Hyde Park. And detached garages, which are the roofs people ignore until a car bonnet gets rained on indoors.

There are also the small ones that cause trouble out of proportion to their size: bay window tops on Roundhay and Chapel Allerton villas, porch roofs, and the little lead or felt flat between two back additions on a through terrace.

What we look at before quoting

The deck comes first. We walk it and probe it. Soft chipboard at the edges usually means the trims have failed and water has been tracking in along the drip for years. Then the fall, checked with a level rather than by eye, because a roof that looks flat to you might be falling in the wrong direction entirely.

Then the outlet. A single 50mm rainwater outlet in the wrong corner will undo a good membrane. We work out where the water naturally wants to go and put the outlet there, adding a second one or an overflow where the roof is large enough to need it.

Finally the edges: the upstand at the house wall, the flashing above it, the abutment where a dormer meets the main slope, and the height available at any door threshold if insulation is going on top.

The build up and what it means for you

A warm deck puts rigid insulation above the deck and the membrane above that, so the timber stays on the warm side and condensation has nowhere to form. It is the right way to build a flat roof now and it is what Building Regulations push you towards on a full recover. It does raise the roof by 100mm or more, which matters if there is a door or a window head close by.

A cold deck puts insulation between the joists with a ventilated gap above. It keeps the height down. It only works if the ventilation is genuinely continuous, and on a dormer boxed in on three sides that is hard to achieve.

Weather and timing

GRP needs dry conditions and a deck temperature above about 5 degrees, which rules out a fair number of days in a Leeds winter. Laying it damp is how you get a roof that crazes and delaminates inside two years, so we book GRP jobs when the forecast supports them and we will move a date rather than rush it.

EPDM is more forgiving and can go down in cooler weather, which is why it takes most of our winter work. Either way the deck goes on and gets sheeted the same day. We do not leave an open deck overnight on a Leeds forecast.

How the work runs

Check the deck and the fall

We measure the fall with a level, find the low spots, and probe the deck. If the boards are soft or the fall is wrong, no membrane will fix it.

Agree the build up

Cold deck, warm deck or a straight recover changes the price and the height at the door threshold. We show you the options and what Building Regulations require on your roof.

Strip and rebuild

Old covering and rotten deck come off, firrings go on to create the fall, then new boards, insulation where needed and the trims.

Lay the membrane and finish

EPDM goes down as one piece on most domestic roofs. Upstands, outlets and edge trims get detailed properly, then we test it with a hose before we leave.

What it typically costs

Job	Typical range
EPDM flat roof, per square metre New deck, insulation where Building Regulations apply, single-piece membrane, scaffold excluded	£95 to £165
GRP fibreglass, per square metre Laid wet on a new ply deck, needs dry weather above 5 degrees	£110 to £185
Torch-on felt, per square metre Three layer system, the cheapest route and the shortest life	£80 to £135
Typical garage or dormer roof Around 12 square metres, stripped, re-decked and recovered	£1,150 to £2,400
Warm deck insulation upgrade PIR board over the deck where a full recover triggers the thermal element rule	£30 to £60 per square metre
Repair to an existing flat roof Patching a split or resetting an outlet where the deck underneath is still sound	£220 to £650

Typical ranges for Leeds and the surrounding area , reviewed September 2026. Every quote is written and fixed before work starts.