The Rectangular Flat Roof Estimating Calculator is used to calculate the labour, materials and plant costs associated with typical rectangular flat roofs. To estimate a flat roof of another shape, use the Universal Flat Roof Estimating Calculator.

The Rectangular Flat Roof Estimating Calculator calculates the following items:

  • Roof joists and wall plates
  • Fascias and guttering
  • Roof waterproofing and perimeter flashings and drips
  • Guttering and down pipes
  • Plastering and insulation
  • Internal and external decorating
  • Plus all labour associated with the above

All of the items required for a flat roof are specified by the specification.


  • Flat roofs can be constructed in several different ways with insulation positioned at various levels and utilising a wide variety of insulation and water proofing systems. It is therefore essential that each of these items are carefully examined within the Specification and/or the Calculated Resources tab and adjusted to accommodate the methods you are using.
  • To add roof lights or skylights to your flat roof, use either the Aluminium Rooflight, PVCu Rooflight or Velux Skylight Estimating Calculator in the Flat Roof Openings section of the Quote Template.