Rubber Extension Roof Kit – Complete 1.2mm One-Piece EPDM Flat Roof System with Gutter, Kerb & Wall Flashing Trims, Cut to Size

A complete one-piece 1.2mm EPDM rubber roof for a flat-roof extension that sits against the house: gutter drip trim along the front, kerb trim down both sides, and a wall flashing where the roof meets the brickwork at the back, with the corners, patches and primer to seal all four.

The 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 hired plant. It is the 1.2mm BBA-certified grade that building control expects on a habitable extension, in 25 sizes up to 7.5m × 7.5m.

Is this the right kit for your roof?

• ✓ A single-storey extension, kitchen extension, side return, garage or utility roof with a flat or low-pitch timber deck from 3m × 3.5m up to 7.5m × 7.5m
• ✓ The roof meets the house wall along one long edge and drains to a gutter along the opposite edge
• ✓ A timber deck — OSB3, WBP plywood or sound boards, warm or cold roof
• ✓ You need the 1.2mm grade with the certificates that building control and insurers ask for

Water runs away from the house to the front edge, which takes the gutter drip trim. The two sides are capped with kerb trim, with a moulded corner at each front corner. At the back the membrane turns 150mm up the house wall and is covered by the wall flashing trim, with a pre-formed corner patch and primer sealing the two back corners where kerb meets wall.

Walls on two or three sides? Side returns and wrap-arounds often need more flashing and fewer kerb trims. Tell us the layout when you order and we will swap the trims at the same price. Free-standing building? You want the garage kit instead, which has kerb trim on three sides and no wall flashing.

Which 1.2mm kit? This one is for roofs against a wall. The garage kit suits detached garages, the garden room kit suits free-standing rooms, the porch kit covers smaller roofs and the dormer kit handles roofs that run under tiles. Anything L-shaped, or with a skylight or outlet, is priced line by line in our roof kit calculator.

What is in the box

What is not included

For a standard rear extension with a gutter at the front and the house wall at the back, nothing else is needed. You may want to add:

• A drain outlet if the roof drains through the deck into a downpipe rather than over the gutter edge
• An EPDM pipe flashing boot where a boiler flue, soil vent or extractor duct passes through
• Extra wall flashing trim if you would rather add a second wall run than have us swap it in
• Walkway pads if the roof is reached from an upstairs window and will be walked on
• Timber, insulation and firrings to build the deck and 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: it dresses down over the front and side edges under the trims, and turns up the house wall at the back. Allow 150mm on each of the four sides. Depth is the dimension from the house wall to the gutter; width runs along the wall.

All 25 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 L-shaped and pitched roofs.

Specification

How it goes on

1. Prepare the deck and the wall

Check every board is fixed, the joints are flush and the falls run away from the house at 1:80 or better. On a re-roof, strip the old covering, replace anything soft, punch every nail head below the surface and fill gaps over 5mm. Rake out or clean the brick course where the flashing will sit, sweep the deck and let everything dry.

2. Relax the membrane, then bond the field

Unroll the sheet with an even overhang on three sides and 150mm spare against the wall, 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 — this one is not left to go tacky — 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 upstand

Brush contact adhesive onto the dry perimeter margin, the wall upstand and the underside of the membrane above them. Wait until both faces are touch-dry, then press the rubber up the wall and down over the front and side edges, and roll it hard. Prime the two back corners and bed the corner patches in.

5. Fit the trims

Trim the surplus membrane, fit the two front corners first, then cut the drip trim and side kerb trims to meet them, screwing at roughly 250mm centres with a 3mm gap at each joint. Fix the wall flashing trim to the brickwork over the top of the upstand and seal its top edge with a bead of sealant.

EPDM against felt and GRP on an extension

What customers say

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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. Everything is cold applied, the membrane arrives as one sheet, and the trims screw on with the corners supplied. The wall detail is the only part that needs care: keep the upstand at 150mm, prime the corners before the patches go on, and seal the top of the flashing. Plan a full day, two people for the larger sizes.

Which size do I need?

Measure the deck from the house wall to the gutter edge and along the wall, add 150mm to each of the four sides, and order the kit closest to but not smaller than that figure. A 3.5m × 4.7m deck needs the 3.8m × 5m kit. Between sizes, go up — or WhatsApp us a photo and your measurements and we will confirm the size before you order.

Will building control accept it?

Yes. The membrane is BBA certified and fire tested to BS 476 and EN 13501, which is what inspectors and insurers ask for on a habitable extension. Email us if you need the certificates for your file.

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, kerb trim for both sides, two front corners, wall flashing trim for the back edge, two back corner patches with primer, a tool kit (rollers, scissors, paint brush) and all clips and pins.

How does the wall junction work?

The membrane turns 150mm up the house wall and is bonded to it with contact adhesive. The wall flashing trim is then screwed to the brickwork over the top of the upstand and its top edge sealed, so water running down the wall is thrown back onto the roof and can never get behind the rubber. The two corners where the side kerb meets the wall are sealed with primed, pre-formed patches.

My extension has walls on two sides

Then you need two wall flashing runs and one kerb trim. Tell us when you order and we will supply that combination instead at the same price, or add a second wall flashing trim to your basket.

Is a drainage outlet included?

No. A standard extension drains over the front drip trim into a gutter. If your roof drains through the deck into a downpipe, add a drain outlet kit.

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

The membrane is lead / slate grey, which stays cooler than black over a living space in summer. The trims come in black, white or anthracite grey — choose above; the price is the same either way. Anthracite matches grey bi-folds and aluminium windows; white matches uPVC fascias.

Can I lay it on a warm roof?

Yes. On a warm deck the membrane bonds to the OSB or plywood that sits on top of the insulation in exactly the same way. Keep the upstand height at 150mm above the finished roof surface, not above the insulation.

How long does it take to fit?

A full day for a typical rear extension: deck preparation, two to three hours to bond the membrane, and two more on the upstand, corners and trims. The largest sizes are 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 old felt?

Only if the felt is fully bonded, flat, dry and free of mineral chippings. On an extension we would usually strip it so you can check the deck and the wall abutment properly first.

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 roof would typically need replacing three to five times over that period.

Does it cope with standing water?

Yes. EPDM is unaffected by ponding water. Build in a fall of 1:80 away from the house anyway so the roof drains and stays clean.

Do I need a primer?

Only for the two back corner patches, and that primer is in the box. 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. If the roof is reached from an upstairs window and will be used more often, fit walkway pads over the membrane. Never walk on it wet or frosty.

How much maintenance does it need?

Ten minutes a year: clear leaves and debris off the roof and out of the gutter, and check the flashing seal and trim joints 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 wall abutment step by step
• Fitting edge trims — which trim goes on which edge
• Forming corners — folding rather than cutting
• Drainage and falls
• Types of EPDM membrane — 1.0mm or 1.2mm?
• The full EPDM Learning Centre