Question answered
Carport roof replacement
The short answer
Carport roof replacement means picking a covering that suits an open structure: polycarbonate for daylight, profiled metal or fibre cement sheets for a solid roof, or felt or a single-ply membrane on a boarded flat frame. Each must be matched to the frame's spacing and fall, with fixings that cope with wind lifting an open roof. A check of the frame itself always comes first.
A carport roof takes wind, sun and rain with no walls to help it. Choosing between polycarbonate, profiled sheets and a felted flat deck comes down to the frame, the light you want and the exposure.
Check what the frame can carry first
Most carport trouble starts below the sheets. Timber posts rot where they meet the ground or a slab, rails sag, and brackets to the house wall loosen. New sheets on a weak frame only hide the problem for a season, so we look at the posts, the beams, the rails the sheets sit on and the fixings to the wall before talking about coverings.
The frame also decides what you can lay. Light twin-wall polycarbonate flexes more than metal and needs rails closer together, while heavier boarded decks need beams sized for the load. Every sheet has a maker's span table and a minimum fall, and the product's own data sheet is the final word. If the rails are too far apart or the slope too shallow, the frame is altered before anything goes on top. Posts set on a slab with no standoff, or buried in soil, are the commonest place for rot to start, and replacing them with a raised base is a modest job when it is done at the same time as the roof.
Polycarbonate, metal and fibre sheets
Polycarbonate lets daylight through, which suits a carport against a house wall where a solid roof would darken a window. It scratches and clouds with age, and thin sheets drum loudly in heavy rain. As a rough pointer from a different roof, HomeBuilding and Eco Experts both put polycarbonate conservatory roofs at around 10 to 15 years, although a carport lives in different conditions.
Profiled metal sheets are light, quick to lay and quieter if given a backing, and coated finishes are chosen for sea air along this coast. Fibre cement sheets suit a traditional garage look. Ask which sheets are going on, what the coating or finish is rated for, and whether the screws and washers come as part of the sheet system, because the smallest parts of a roof are often the first to fail. Our page on weighing price against life on a garage roof covers the same trade-off, and the same sense applies when sheets are chosen for a carport.
Open sides make wind the main test
A carport roof behaves like a sail. With open sides, air pushes up beneath the sheets as well as over them, and the lift concentrates at the windward edge. Marley notes for tiled roofs that pitches under 30° can suffer severe suction on the side facing the gusts, and the same physics applies to a lightly pitched sheet roof.
So we examine how the sheets are held down, as well as what they are. Fixings should pass through the crest of the profile into a solid rail, with washers sized for the sheet, and the laps should be arranged so gusts cannot get under an exposed edge. Clips that were fine on a sheltered street can pull out near the seafront or on the open Downs side. The posts are checked to confirm they resist the same uplift as the roof above them, and the brackets that tie the carport to the house wall get the same attention, since a loose wall plate lets the whole roof flex.
Felt and membrane carport roofs
A flat carport with a boarded deck can be covered in felt, in a rubber membrane called EPDM, or in glass-reinforced plastic (GRP). MyBuilder (updated 21/08/2026) quotes garage roof prices of about £75 per m² for felt and £70 to £100 per m² for EPDM as typical UK ranges, a rough guide to the scale of the work and not a price. The written quote that follows the survey carries a single total.
Fall is the important detail. IKO, citing the 2018 edition of BS 6229 (since revised), recommends a finished minimum slope of 1:80 on a flat roof, and suggests designing for 1:40 to leave room for sag in the deck and small errors in the build. A carport deck laid dead level ponds, and ponding shortens the life of any covering. Edges also matter: a carport roof has no wall to shelter it, so drip edges and upstands at the house wall need careful detailing. If you want a pitched carport instead, see pitched garage roofs for what changes.
Old sheets, enclosing the carport and attachment
Sheets that went up before 2000 are treated as containing asbestos until tested, which is HSE's advice for buildings of that age. Do not drill, break or wash them; our guide to replacing one garage roof sheet explains why even a single panel needs a plan.
If you are thinking of walling the carport in, read what the roof needs in a garage conversion first, since an enclosed space asks more of the roof. Whether a carport needs planning permission or building control approval turns on its size and position, so put that question to the Adur and Worthing planning team before the structure is altered. Send photographs of the posts, the sheets and the wall fixings and we can say what looks realistic. The full range is on our garage roof replacement page.
Carport roofs: two more points
Can clear polycarbonate go over my existing carport rails?
Often, but the rails may need adding to, because thinner light sheets span less and flex more than metal ones. Check the sheet maker's span table against your rail spacing, and confirm the fall suits the sheet before ordering anything. We measure the existing rails at the survey and say whether they will do.
How do I find out whether old carport sheets are asbestos?
You cannot tell by looking. Sheets from before 2000 should be treated as asbestos until a sample says otherwise, so leave them alone and do not clean or drill them. Our page on testing an asbestos roof explains how identification works, and we will not touch suspect sheets before the result is in.
Tell us about your roof
Describe what is happening and we will call you back to arrange a visit.
- Photographs of what we find
- A written quote with one total price
- Or call 01903 299063
10-year workmanship guarantee, in writing.