The short answer
They are good for the right building. Corrugated bitumen sheets are light, cheap to buy and easy to cut, which makes them a fair choice for a shed, a lean-to store or a basic garage. They have limits. They soften in strong sun, sag between supports if the frame is too wide, and look dated beside a house. For a garage you value, other coverings last longer.
Bitumen sheet is the black ribbed board you see on sheds and allotment stores. It is a practical product with a short list of limits.
What the sheets are
A corrugated bitumen sheet is a fibre board soaked in bitumen and pressed into a wave. Bitumen is the same tar-like substance found in roofing felt. The sheets are light enough for one person to carry, and a fine-toothed saw cuts them to fit.
Why do people choose them?
Price and speed. A small shed roof can be covered in an afternoon, and the product is forgiving. It tolerates being cut on site and fixed to simple timber rails without special tools. If you are swapping an old fibre-cement roof for something new, ask the supplier to confirm in writing what the new sheet is made of, so you know what is going up in its place.
Bitumen sheet is a wavy board and not a tile, so it relies on its overlaps and its fixings to keep water out. The maker's data sheet gives the side lap, the end lap and the minimum pitch for each product. Before anyone orders, we measure the slope on your garage and set it against those figures.
That check matters because a sheet laid below its stated pitch leaks at the laps, however carefully it is fixed. A shallow garage roof is the usual place for that mistake.
Where bitumen sheets suit and where they do not
These sheets work on small, simple buildings with a modest span and a sound frame. A potting shed, a bin store, a log store or a lean-to against a boundary wall are all fair uses. The roof does not need to carry heavy loads, and nobody expects a showpiece finish.
Are they right for a garage?
It depends on what the garage is for. For a basic store with no heating and no one working under it, they can do the job. For a garage holding a car, tools and boxes you care about, or a building that faces the road, we would steer you toward a covering with a firmer surface and a longer expected life, such as a coated steel sheet or a felt or rubber membrane.
Heat affects them. In strong sun the bitumen softens, and a sheet can droop between rails that are spaced too far apart. Rails at close centres reduce that, so the framework counts as much as the sheet. In cold weather the sheets stiffen and can crack if they are struck or fixed too tightly.
The main alternatives are compared on our best garage roof material page.
Fixings, fading and condensation
Bitumen sheets are fixed with special screws or nails that have a large sealing cap, and the fixings go through the crown of each wave, never the trough. A fixing in the trough lets water settle around it and find its way in. Using too few fixings is another cause of failure, because wind lifts a corner and then the whole sheet works loose.
Do bitumen sheets fade and drip?
Colour fades over the years as sunlight wears the surface, and a dark sheet can turn dull. That is cosmetic. Dripping from the underside is a separate matter. Like any thin roof over a space with damp air, the underside can collect moisture on cold mornings, and a garage with poor ventilation will show it. The answer is airflow, which means gaps at the eaves and ridge ends and no stacked boxes pressed against the wall.
Length of life depends on the installation. Sheets fixed through the crowns with proper caps, on rails at close centres, outlast the same sheets thrown over old, bowed timbers. The condition of the roof timbers is the first thing we check, and we show you the evidence.
Cost and the better buy
Bitumen sheets are among the lower-cost coverings to buy. The saving can disappear if the frame needs repair, if the old roof has to be taken away, or if the sheets have to be replaced again early. A cheap material that needs replacing sooner is not the cheaper roof.
What does a garage re-roof cost in general?
In MyJobQuote's October 2026 guide, replacing a garage roof sits between £750 and £3,500 as a typical UK range, across all coverings. The surface chosen, roof area, access, tower hire and disposal of the old roof all push the figure up or down. If the existing sheets are asbestos cement, a separate set of handling rules applies, set out on our asbestos garage roof removal page.
We look at the building first. If bitumen sheet suits a garden store you rarely open, that is what we recommend. If your garage would be better served by another covering, we explain why, using pictures taken on your own roof. Our corrugated garage roof replacement page covers the other corrugated options, and the garage and asbestos roofs page sets out the full service. A single written total follows the visit.
More on bitumen sheeting
Can bitumen sheets be laid over old corrugated sheets?
Over sound, non-asbestos sheets they sometimes can, if the frame will carry the extra load and the profiles line up. Over asbestos cement it is a different matter, because fixing through the old sheet disturbs it. We identify the old material before suggesting anything, then explain the options.
How steep does a bitumen sheet roof need to be?
Every product has its own minimum pitch, and the maker's data sheet states it. Laying sheets below that pitch invites leaks at the laps, even with good fixings. We measure your slope with a level and match it to the product before anything is ordered.
The full picture: Garage and asbestos roof replacement in Taunton · More short answers