Garden Shed Roof: Felt, EPDM or Onduline by Pitch

A garden shed roof is usually the first part of a shed to fail, and in autumn it is the part worth checking before the wet months set in. Most sheds leave the factory with a single layer of green mineral felt nailed over thin boards. That covering does its job for a few years, then it cracks, lifts at the edges and lets water into the boards underneath. Once the boards are wet, the problem stops being a £30 roll of felt and becomes a new roof deck.

This covers how to tell whether your shed roof needs work, which covering suits which roof pitch, what each one realistically lasts, and how to refelt a shed roof properly if felt is still the right answer.

Signs your garden shed roof needs work

Go up a stepladder on a dry day and look at the felt, then go inside and look at the underside of the boards with a torch.

Worn brown felt shingle shed roof with two domed rooflights and nail heads showing across the courses — A worn shingle shed roof, with nail heads showing through the courses | Shed roof by A.M. Kuchling (CC BY 2.0), via Flickr, https://www.flickr.com/photos/44165698@N00/17294115

Cracks and crazing across the felt, often worst on the sunny side where UV has dried out the bitumen.
Blisters and bubbles, which trap water and split open with the next frost.
Lifting edges at the eaves and gables, where wind gets under the felt and tears it from the nails.
Nail heads showing or rusting through, a sign the covering has thinned or the boards have shrunk.
Moss and algae holding water against the surface, typically under overhanging trees.
Inside: dark stains, soft spots or daylight between the boards. Push a screwdriver into any stained patch. If it sinks in, that section of deck is rotten and has to come out before any new covering goes on.

If the boards are sound and only the felt is tired, you can simply refelt. If boards are soft or the roof sags between the frame, replace the deck first. New felt nailed to rotten timber will pull through within a winter.

Garden shed roof materials compared

Each covering has a minimum pitch below which it will not shed water reliably, so start with the shape of your roof. An apex shed usually has a pitch steep enough for most options; a pent (single slope) shed is often shallow, and a near-flat roof narrows the choice to felt systems or EPDM.

Covering	Typical life	Minimum pitch	Best for
Standard shed felt	About 5 to 10 years	Low pitch, not truly flat	Cheap refresh on a sound deck
Heavier “super” shed felt	Up to 15 years (maker’s claim)	Low pitch	Better felt at modest extra cost
Felt shingles	Roughly 10 to 25 years	About 12.5 degrees	Apex sheds and summer houses
Onduline (corrugated bitumen)	15-year waterproofing warranty	5 degrees on boards, 10 on purlins	Pent roofs, open log stores
EPDM rubber	Often 20 years plus	Flat or low pitch, with a fall	Pent and flat roofs, garden offices
Metal box profile	Depends on coating, 8 to 25 years plus	About 4 degrees	Workshops, bike stores

Lifespans vary a lot by source and by how well the roof is fitted and kept clear; treat the figures above as ranges, not promises. IKO, which makes much of the UK’s shed felt, says its Super Shed Felt lasts up to 15 years but still advises checking and replacing shed felt every 5 to 10 years.

Shed felt

Mineral felt is a bitumen sheet with a mineral chipping surface, sold in rolls, usually green or grey. It is the cheapest option and the easiest to fit with a hammer and clout nails. Cheap sanded felt is intended as an underlay beneath shingles, not as a finished covering, so check the label. Felt is fine on a small apex shed if you accept refelting every several years.

Felt shingles

Shingles are strips of bitumen felt cut to look like tiles, nailed in overlapping courses over a felt underlay. They look far better than roll felt, which is why many summer houses use them, and a damaged strip can be replaced on its own. They need a steeper pitch than roll felt, and in exposed gardens the tabs can lift in high winds until the self-seal strips bond in warm weather.

Onduline and corrugated sheets

Onduline is a corrugated sheet made from bitumen-impregnated fibres. It is light, at about 3.4kg per square metre, and quick to fix. Onduline states a minimum pitch of 5 degrees on a solid deck of OSB or plywood, or 10 degrees on purlins. It is a good fit for pent sheds and log stores where a felt roof keeps tearing.

EPDM rubber

EPDM is a synthetic rubber membrane bonded to the deck. For most sheds it comes as one piece cut to size, so there are no seams on the main roof, which is where felt roofs usually leak. It is the best option for flat and low-pitched shed roofs and for garden offices, where a leak means damaged equipment, not just damp tools. It costs more than felt, needs a smooth, clean OSB or ply deck, and must be finished with edge trims. Give the roof a slight fall so water does not pond.

Check the roof deck before you choose a covering

Most budget sheds have a roof of thin tongue-and-groove boards or thin OSB sheet. Neither is designed to carry much weight, which matters if you plan to stand on the roof to fit it. Spread your weight with a board across the rafters rather than kneeling on the middle of a panel.

When you strip the old felt:

Pull out or hammer home every old nail and tack so nothing punctures the new covering.
Replace any soft boards. Match the thickness so the surface stays flat.
If the boards have gaps or are uneven, overlay the whole roof with OSB3 or exterior plywood. This is essential for EPDM and Onduline at low pitches, and makes felt last longer too.
Check the fascia boards and bargeboards. Rotten fascias are where felt edges pull away first.

How to refelt a shed roof

These steps follow IKO’s published shed felt instructions for a roll-felt apex roof. Pick a dry, calm day; felt is stiff and cracks when cold, so unroll it and let it relax in the sun or a warm room first.

Measure and cut. Cut lengths to run along the roof, allowing about 50mm of overhang at the eaves and at each gable end.
Start at the bottom. Lay the first strip along the lowest edge so it overhangs the eaves by 50mm. Nail the top edge with galvanised clout nails at about 500mm centres.
Fold and fix the edges. Fold the overhangs down over the fascia and nail them at roughly 50mm intervals. Fold the corners neatly rather than cutting them.
Work up the roof. Lay each next strip so it overlaps the one below by 75mm, stick the overlap down with felt adhesive, and fix it the same way.
Finish the ridge. On an apex roof, run a final strip over the ridge so it laps down both slopes, bond it with felt adhesive and nail it closely.
Refit the fascias and bargeboards over the folded edges so the wind cannot get under them.

For a pent roof, the same principle applies: start at the lowest edge and lap each strip over the one below, so water always runs over a joint, never into it.

Gutters, overhangs and what makes a shed roof last

How long a roof lasts depends as much on what surrounds it as on the covering.

Clear leaves and moss each autumn. Debris holds water against the felt and speeds up rot at the eaves.
Cut back branches that brush the roof. They scour the surface in the wind.
Add a gutter on the low side and run it into a water butt. It stops water splashing back onto the cladding and base, which is where many sheds rot first.
Keep a gap from fences and walls. A shed jammed against a fence cannot dry out, and you cannot reach the roof edge to maintain it.

If you are raising the roof or rebuilding the shed, remember the permitted development height limits for outbuildings. Our guide to planning permission for a garden shed sets out the 2.5m rule near boundaries. For insulated garden buildings, our garden room roof guide covers warm-roof build-ups.

Frequently asked questions

How often should a shed roof be refelted?

Standard shed felt usually needs replacing every 5 to 10 years, depending on exposure, sun and how well it was fitted. Heavier felts last longer. Check it every autumn and patch small splits with felt adhesive before they let water into the boards.

What is the best material for a flat shed roof?

EPDM rubber is generally the best choice for a flat or very low-pitched shed roof, because it goes on as a single sheet with no joins and copes with standing water far better than felt. Give the roof a slight fall and fit proper edge trims.

Can I put new felt over old felt?

It is better not to. Nailing over old felt hides rotten boards, traps moisture and gives the new nails a poor fixing. Strip the old covering, check the deck, replace any soft boards and then refelt.

Can you fit Onduline on a shed roof with a low pitch?

Onduline sheets can go down to 5 degrees if they are laid over a solid deck of OSB or plywood. Below that, use EPDM or a felt system instead.

Why is my shed roof leaking when the felt looks fine?

Check the ridge, the edges and the nail holes. Leaks often start where felt has pulled away from the fascia, at a poorly lapped joint, or around nails that have lifted. Water can also track in along the top of the cladding if there is no overhang or gutter.

For more practical advice on garden buildings, from sheds to fully insulated rooms, explore Best Garden Room.