Headroom shortfall

Designs that work on paper fail when the existing roof timbers, insulation and new floor build-up are added. Measure on site before signing off the design.

Missing fire protection

Plasterboard fitted, painted and decorated — then Building Control flag missing fire-rated boards above the stair. Open-up and redo is the only remedy.

Insulation in the wrong place

Warm roof vs cold roof confusion is endemic. Get the build-up right at design stage; do not let it be decided on site.

Steelwork without details

Padstones, bearing lengths, connections and fire protection of steel routinely missed. The engineer's drawings should be on site, and the builder should be working to them.