You can usually tell the two apart with a careful look inside the attic, and the difference matters because it shapes how a conversion is approached. The quickest test is whether the space is open or blocked with timber.
A traditional cut roof is built on site from rafters and purlins, and it looks open. You will see big diagonal timbers around the edges, with a clear central space you can move through. Cut roofs are common in older houses, broadly those built before the 1970s and 1980s, and they usually offer an open, convertible space.
A modern trussed roof is made from prefabricated W-shaped timber trusses. It looks criss-crossed with lots of smaller timbers forming W shapes, and you cannot walk through it because the webbing fills the space. Trussed roofs are common in newer estates.
- Cut roof: open feel, large diagonal timbers around the edges, room to move.
- Truss roof: dense criss-cross of small timber W shapes you cannot pass through.
Why it matters: a cut roof usually converts more directly, whereas a trussed roof can still be converted but needs a structural engineer to design new steels and floor structure to replace the trusses, which adds cost. Head height then decides whether a Velux approach works or a dormer is needed.
If you are still unsure after looking, we can identify it for you during a free assessment, or you can start with our suitability checker.