Carport roof options

A garage has walls on four sides to hold its roof steady. A carport usually has posts, a beam and some rafters, and often one side fixed to the house. Because wind can get under and around the covering, the frame matters more than it does on an enclosed building. Posts rot at the foot where timber meets a concrete pad. Steel posts rust at their base plates. Bolts work loose in the beam, and a rafter that has been bowed for years will not carry a heavier covering without help.

So the first job is to inspect the supports. We check posts for movement, how the roof is tied to the house, how the rafters fall and whether the timber is sound. If any of that is weak, strengthen the frame first and cover it second. A new covering fixed to a tired frame fails at the weakest bolt, not at the sheet.

Photographs of every post, the beam and the underside of the roof are what we ask for when you first get in touch.

Four materials account for most carport roofs, and each has a use.

• Polycarbonate sheet. Light, easy to fit and it lets daylight through, which helps when the carport sits against a kitchen window. Twin-wall is stiffer and warmer than single skin. Sources put polycarbonate conservatory roofs at around 10 to 15 years, and the sheet fitted to a carport is the same material, so plan on a similar working life rather than a lifetime.
• Box-profile or corrugated steel. Strong, quiet when it has a good coating and cheap to hold up because it is light. Noise in heavy rain and condensation underneath are its weak points. Our guide on box-profile steel roof sheets goes into the detail.
• EPDM on a flat deck. EPDM is a synthetic rubber membrane laid as one sheet. It gives a clean look and few joints. Typical life is 20 to 30 years or more, according to GreenSpec, though that depends on the deck beneath.
• GRP. Fibreglass moulded in place over boards. It is hard-wearing and shapes well round rooflights and odd corners.

Flat or low-pitched carports fail where water stands. On a flat roof, BS 6229:2018 as reported by IKO sets a recommended finished fall of 1:80 at the least, and designers aim for 1:40 so that tolerances and sag leave some margin. Many old carports were built dead level, which is why they hold puddles and stain at the edges.

Sheet roofs need enough pitch for their laps to shed water, and the fixing pattern has to suit the sheet. Screws go through the crown of a steel profile, or through the flat of a polycarbonate sheet with an oversized hole and a sealing washer, so the sheet can expand and contract without cracking. Too few fixings lets a sheet lift in a gust.

Do not forget the edge. A carport beside a house needs a flashing or a sealed upstand where the roof meets the brickwork, otherwise rain tracks down behind the covering and into the wall. Gutters and a downpipe to a soakaway or drain keep the pad dry and the neighbour happy.

Occasionally, yes, but not by default. Marley lists its concrete plain tile at 73.8 kg/m² laid, which is a long way beyond a sheet of steel or polycarbonate. A frame built for light sheeting needs to be checked, and usually uprated, before it carries that weight. Beams may need to be deeper, posts may need larger foundations and the connection to the house wall may need a rethink.

When we do tile a carport, it is usually because the carport adjoins a pitched house roof and the owner wants it to match, or because a conservation area makes plastic sheet unwelcome. The cost of the extra structure is often a good reason to choose a lighter alternative that looks right from the street, so that is what we talk through at the survey.

A close look at the existing covering usually shows whether repair is worth it.

Planning permission or Building Regulations approval may apply to a carport, depending on its size, its distance from a boundary and whether it is fixed to the house or stands alone. Listed status matters too. A photograph cannot settle any of that. Put the question to the planners at Swindon Borough Council, or at whichever council covers your address, before you alter the footprint or the height. Re-covering like for like is a lighter question than building new, though a phone call is still sensible in a conservation area.

Where the carport is shared, or sits on a rented plot, the question of who pays and who may alter it comes before any question of material. Our page on garage block roofs covers the same ground for lock-up blocks. If you plan to sell, a damaged asbestos sheet carport roof will show up in surveys, so read selling a house with an asbestos garage roof first.

Owners sometimes want light under a carport, particularly where it blocks a window or a back door. Twin-wall polycarbonate panels are one answer, and where the roof is a solid covering a rooflight can be added. Our page on adding a skylight to a garage roof explains how that works on sheet and flat roofs.

We photograph your carport during the survey, and the quote you receive afterwards is written and gives one total. Size, frame work, height, access for a tower or ladders and the covering itself all push it up or down. Ask any firm whether VAT and scaffolding are inside their figure. A written guarantee covers our workmanship for a decade, and old materials leave with us. To begin, WhatsApp pictures of the posts, the roof from below and a rough width and length, or ring 01793 626096. The wider picture sits on our garage roof replacement page.