Felt, EPDM or corrugated sheets — what should I put on a shed roof?
What each shed roof covering actually costs you in life, labour and pitch, and the two questions — roof pitch and deck condition — that decide most of it.
- Difficulty
- beginner
- Time
- 20 min
- Read
- 4 min
Short answer
Mineral felt is cheapest and lasts ten to fifteen years. EPDM rubber is a single seamless sheet, handles flat and very shallow roofs and lasts two or three times as long. Corrugated bitumen sheet is quickest over a rough or uneven deck but needs a reasonable pitch. Shingles look best, cost most in time, and need the pitch the manufacturer specifies. Check your roof's pitch first — it rules options out.
Every shed roof covering is a trade between initial cost, working life and how forgiving it is about the deck underneath. There is no single best answer, but there is usually one obvious answer once you know two things: how steep the roof is, and whether the boards under the old covering are sound.
Step by step
- Measure the pitch before you choose anything.Hold a level horizontally against the slope and measure the drop over a known length. A flat or near-flat roof — under about 10 degrees — rules out shingles and makes corrugated sheet marginal. Steeper roofs open every option.
- Strip a corner and look at the deck.A sound deck takes any covering. A rough, patched or uneven deck suits corrugated sheet on battens, which bridges unevenness, or needs re-boarding before felt or EPDM, both of which telegraph every lump.
- Decide how long you want it to last.Felt on a shed you will replace in ten years is a rational choice. EPDM on a garden office you intend to keep is equally rational. Matching the covering's life to the building's is the whole decision.
- Be honest about the work involved.Felt is the easiest to handle and the fiddliest to detail. EPDM is one sheet with almost no detailing but is unforgiving about surface preparation and temperature. Corrugated sheet is fast but the fixings and the ridge piece have to be right. Shingles are a day's patient work on a small roof.
- Check the ridge and edge details are available as a set.Every system has a matching ridge piece, edge trim or eaves detail. Buying the field material and improvising the edges is how these roofs fail. Buy the system.
- Factor the weather window.EPDM adhesives and felt adhesives both have a minimum temperature and both need dry conditions. Corrugated sheet can be fitted in almost anything. If you are doing this in November, that matters more than the price difference.
Common mistakes
- Choosing a covering that the roof pitch will not support — Every covering has a minimum pitch below which wind drives water back up the laps. Shingles and corrugated sheet both have one; ignoring it produces a roof that leaks only in driving rain, which is the hardest kind of leak to diagnose.
- Laying a long-life covering over a deck that will not last as long — EPDM on rotten 9mm boards is thirty years of membrane on ten years of substrate. Re-deck first or use felt.
- Buying the field material without the trims — Ridge pieces, edge trims and corner pieces are what make the system watertight. Improvised edges are the reason a new roof leaks in its first winter.
Alternatives
- Mineral shed felt: The default. Cheap, available everywhere, ten to fifteen years on a well-detailed roof, less on an exposed one. Laid in overlapping courses bedded in adhesive. Weak points are the nails, the ridge and the edges, all of which are detailing rather than material problems.
- EPDM rubber membrane: A single synthetic rubber sheet cut to size, bonded to the deck with contact adhesive, with formed corners and edge trims. No laps in the field, so nothing to fail. Life measured in decades. Needs a smooth, clean, dry deck and mild still weather to fit, and the sheet must be sized right first time.
- Corrugated bitumen sheet: Lightweight sheets screwed through the corrugation crowns with sealing washers, onto battens or directly to a deck. Tolerant of an uneven substrate, fast to fit, easy to walk on if battened correctly. Needs a decent pitch, proper end and side laps and a matching ridge piece, and looks like what it is.
- Felt shingles: Strips of mineral felt nailed in courses over a felt underlay so each course covers the fixings of the one below. The best appearance by a distance and the one that makes a garden building look like a building. Needs the pitch the maker specifies and takes real time on anything larger than a small apex roof.
- Profiled metal or plastic sheet: Common on stores and lean-tos. Very long-lived and very noisy in rain, and it condenses heavily on the underside unless it has an anti-condensation backing or a ventilated void. Fine for a log store, poor over anything you want to keep dry things in.
Questions people ask
Can I put EPDM on a pitched apex roof?
Yes — it is not only a flat roof product. On an apex roof it goes over the ridge in one piece, which removes the weakest point of a felt roof entirely. The limiting factor is getting a sheet large enough and bonding it evenly on a slope.
Is felt really only good for ten years?
Good felt, well detailed, on a sheltered roof with a decent pitch, can go longer. Cheap felt on an exposed flat roof with nails through the field can fail in five. The material matters less than the detailing and the exposure.
What about painting the old felt with a liquid coating?
Liquid roof coatings work on a sound, clean, dry surface and buy time on a roof that is weathered but not cracked. They do not bridge splits, they do not stick to a wet or mossy surface, and they are not a substitute for re-covering a brittle roof.