Craft Quantities
Plan & Takeoffs

By trade

Roofing calculators

Every roofing quantity starts with an area that is not on the plan. A 30° roof covers about 1.155 times the footprint beneath it, a 45° roof 1.414 times, and an estimate built on the plan area is short by that factor before a single tile is counted.

  • 47Calculators
  • 4Parts of the site

How roofing is measured

Square metres on the slope for coverings and underlay, linear metres for every edge — ridge, hip, valley, verge, eaves and abutment — and counts for fixings at a schedule set by the exposure. Slates and tiles are then ordered by the course, which is a function of the lap rather than of the area.

Where roofing sits on this site47 across 4
47

Renovation & Construction12

Insulation & Efficiency1

Materials & Quantities33

Sustainability & Compliance1

What gets left off a roofing order

  • Double courses at the eaves and the cut course at the ridge, both of which use more material per metre than the field.
  • Valleys and hips: the cutting waste along a diagonal is material bought and thrown away, and it grows with the tile format.
  • Fixings to the exposure zone rather than to the manufacturer's minimum — a perimeter and a corner zone take more than the middle of the roof.
  • Everything that penetrates: vents, boots, soil pipes and rooflights each take a flashing, a cut and a labour item the area never shows.

Job takeoffs11

Where roofers meet the rest of the job: each runs one of these calculators, with every other trade in the same job beside it.

Worked examples2

A real job estimated step by step, with this trade's steps counted.

Comparisons16

Two ways of doing the same work, weighed against each other.

Planners2

Work this trade out from a space rather than from a job.