Rubber Dormer Roof Kit – Complete One-Piece EPDM System for Flat-Top Dormers, Cut to Size

A complete one-piece EPDM rubber roof for a flat-top dormer, built around the way a dormer actually drains: a gutter drip trim along the front edge, kerb trim capping the two sides, and the membrane running up under the tiles or slates where the flat roof meets the pitched roof behind.

The 1.2mm membrane is cut to your chosen size before it leaves us, so it goes on as one sheet with no on-site joining, and everything is bonded cold — no torch, no flame, no hot works next to the timber and felt of a pitched roof.

Is this the right kit for your roof?

• ✓ A flat-top dormer — box dormer, loft-conversion dormer or a run of dormers — with a timber deck from 1.5m × 2m up to 4.5m × 9m
• ✓ The front edge drains to a gutter and the back edge meets a pitched roof of tiles or slates
• ✓ A timber deck — OSB3, WBP plywood or sound boards
• ✓ You want the whole job in one delivery, fitted in a day with no flame anywhere near the roof timbers

Water runs forward to the front edge, which takes the gutter drip trim with a moulded corner at each end. The two sides are capped with kerb trim. At the back the membrane runs 150mm up the pitched roof and tucks under the bottom course of tiles or slates, so rainwater coming down the main roof sheds straight onto the rubber. The two back corners, where the kerb meets the pitch, are sealed with pre-formed corner patches on primer.

Dormer built against a wall, or a porch? Use the porch kit, which swaps the pitched-roof detail for a wall flashing. Cheeks clad in slate or tile hanging? The kerb trim still fits; tell us and we will cut the trims to suit. Anything with a skylight, a pipe or an odd shape is priced line by line in our roof kit calculator.

What is in the box

What is not included

For a standard flat-top dormer, nothing else is needed. You may want to add:

• An EPDM pipe flashing boot where a soil vent or flue passes through the dormer roof
• A drain outlet if the dormer drains through the deck rather than over the front edge
• Replacement tiles or slates for the course you lift at the back, if any break on the way out
• Timber and firrings to correct the falls — sourced locally, not something we ship

Choosing the right size

The size on this page is the size of the membrane, not your roof.

The rubber has to reach past the deck on every side: over the front and sides under the trims, and 150mm up the pitched roof under the tiles. Allow 150mm on each of the four sides. Depth is the front-to-pitch measurement; width runs along the gutter.

All 52 sizes are listed in the selector above, each with the deck it fits. If you fall between two sizes, take the larger one. Surplus membrane trims off in seconds; a sheet 50mm short cannot be rescued.

Size and price my roof Our calculator prices every line for any shape, including skylights and L-shaped roofs.

Specification

How it goes on

1. Prepare the deck and lift the back course

Take the old covering back to the boards. Replace anything soft, punch every nail head below the surface, fill gaps over 5mm and confirm the falls run to the gutter edge at 1:80 or better.

Carefully lift the bottom course of tiles or slates where the pitched roof meets the dormer and set them aside; the membrane will tuck under them. Sweep the deck clean and let it dry.

2. Relax the membrane, then bond the field

Unroll the sheet with an even overhang all round and leave it 30 minutes to lose its fold memory. Fold half back and roller water-based deck adhesive onto the bare deck, stopping about 150mm short of every edge.

3. Sweep it down into the wet adhesive

Roll the folded half back into the adhesive while it is still wet and sweep it firmly from the fold outwards with a soft broom to drive the air out. Repeat for the second half.

4. Contact-bond the perimeter and the pitch

Brush contact adhesive onto the dry perimeter margin, the first 150mm of the pitched roof under the lifted course, and the matching underside of the membrane. Wait until both faces are touch-dry, then press the rubber over the front and sides and up the pitch, and roll it hard.

Fold and bond the two back corners, then prime them and apply a corner patch over each. Re-lay the tiles or slates over the membrane.

5. Fit the trims

Trim the surplus membrane, fit the two moulded front corners first and cut the gutter and kerb trims to meet them. Screw through the face at roughly 250mm centres with a 3mm gap at each joint.

Why rubber instead of felt or lead on a dormer

What dormer owners say

Read all customer reviews · Rated Excellent by 1,000+ UK roofers on Trustpilot.

Delivery, dispatch and returns

• Free delivery to UK mainland addresses on every size — including the trims, which most suppliers surcharge.
• Dispatched within one working day — every membrane is cut to your size before it leaves.
• 1–3 working days on a tracked courier once dispatched. Trims travel in a separate rigid pack so they arrive straight.
• Made to measure — the membrane is cut to the size you order, so kits cannot be returned or exchanged once cut unless faulty. Faulty or damaged items are replaced or refunded in full.
• 20-year product guarantee on the membrane; BBA and fire certificates available on request.

Frequently asked questions

Can I fit this myself?

Yes, if you are comfortable working at height on a pitched roof. The field of the dormer goes down like any EPDM sheet; the part to take slowly is lifting the back course of tiles, tucking the membrane under and re-laying them. Everything is cold applied, so there is no torch anywhere near the roof timbers. Plan a full day and work from a properly secured ladder or scaffold.

Which size do I need?

Measure the dormer deck, add 150mm to each of the four sides, and order the kit closest to but not smaller than that figure. A 1.7m × 2.7m deck needs the 2m × 3m kit. Between sizes, go up — or WhatsApp us a photo and your measurements and we will confirm the size before you order.

Which way round are depth and width?

Depth is the measurement from the gutter edge back to the pitched roof. Width runs along the gutter. A 2m × 4m kit is 2m deep and 4m wide, and the trims are cut to suit that layout.

How does the membrane join the pitched roof at the back?

You lift the bottom course of tiles or slates, run the membrane 150mm up the pitch on contact adhesive, and re-lay the tiles over it. Rain coming down the main roof then runs off the tiles straight onto the rubber. No lead, no mortar and no soakers are needed on a straight junction. The two corners where this meets the kerb trim are sealed with the patches supplied.

My dormer has a wall at the back, not a pitched roof

Then you want the porch kit, which has the same gutter and kerb trims but a wall flashing trim for the back edge instead of the under-tile detail.

Will the membrane have a join?

Every kit is supplied as one sheet at the size you order, so there is no on-site joining required — nothing to tape or overlap on the roof.

As with all EPDM sheet, larger sizes may contain a factory-made join formed under controlled conditions; these are covered by the product guarantee.

What exactly is included?

1.2mm EPDM membrane cut to size, water-based deck adhesive, contact adhesive, gutter drip trim for the front edge, kerb trim for both sides, two moulded front corners, two corner patches with primer for the back corners, a tool kit (scissors, roller set, mini roller, paint brush) and all clips and pins.

What colour is the membrane, and can I choose the trim colour?

The membrane is lead / slate grey, which sits well next to slate and grey tile. The trims come in black, white or anthracite grey — choose above; the price is the same either way. White suits uPVC fascias, anthracite matches grey windows.

How long does a dormer roof take to fit?

A full day for a single dormer, most of it on preparation, lifting and re-laying the back course and fitting the trims. The membrane itself goes down in an hour or two. A full-width loft dormer is a two-person day.

Does the deck have to be dry, and what weather do I need?

Yes. The deck must be completely dry and you want a dry day at 5°C or above with no rain forecast until the adhesive has cured. Water-based adhesive will not bond to a damp deck, and trapped moisture blisters the finished roof.

Can I lay EPDM over the old felt?

On a dormer we would strip it. Old dormer decks hide soft boards you cannot see through felt, and you need a clean deck to form the back detail properly. Overlaying is only sensible if the felt is fully bonded, flat, dry and free of chippings.

How long will it last, and is it guaranteed?

The membrane carries a 20-year product guarantee and has a life expectancy of up to 50 years. Felt on the same dormer would typically need replacing two to four times over that period.

Is the membrane certified?

Yes — it is BBA certified and fire-tested to BS 476 and EN 13501. If your building control officer or insurer wants the paperwork, email us and we will send the certificates.

Does it cope with standing water?

Yes. EPDM is unaffected by ponding, which matters on older dormers where the falls are rarely perfect. Build in a fall of 1:80 from the pitch to the gutter anyway so the roof drains and stays clean.

Do I need a primer?

Only where supplied: the primer in the kit is for the two corner patches. The water-based adhesive bonds directly to OSB and plywood without it.

Can I walk on the finished roof?

For occasional maintenance in soft-soled shoes, yes. Most dormer roofs are never walked on, but if yours is used for window cleaning or gutter access, fit walkway pads and never walk on it wet or frosty.

How much maintenance does it need?

Ten minutes a year: clear leaves off the roof and out of the gutter, and check the trim joints and the back corners after big storms. There is nothing to re-coat or paint.

When will it arrive?

Every kit is dispatched within one working day, then 1–3 working days on a tracked courier. Delivery is free to UK mainland addresses, trims included.

What if I order the wrong size?

Tell us straight away. Every membrane is cut to your size to order, so once it has been cut it cannot be returned or exchanged unless it is faulty. If you contact us before the membrane is cut we can amend the size free of charge — which is why we would rather size it with you first.

Guides that go with this kit

• Flashing and detailing — the pitched-roof junction explained
• Fitting edge trims — which trim goes on which edge
• Forming corners — folding rather than cutting
• Drainage and falls
• The full EPDM Learning Centre