Roofing Calculators

Roofing in the UK must withstand the country's varied and often harsh weather conditions, from driving rain in the west to heavy snowfall in Scotland and high winds along coastal areas. The choice of roofing materials, underlays, and fixings must account for local exposure zones as defined in BS 5534 (the British Standard for slating and tiling) and BS 8104 for wind-driven rain exposure. Our roofing calculators help you quantify materials accurately for any UK roof type, from traditional pitched slate to modern flat roof membranes.

Concrete roof tiles remain the most popular choice for UK new-builds and re-roofs, with Marley, Redland (now BMI), and Russell being the dominant manufacturers. Common profiles include the Marley Modern (plain interlocking tile at approximately 10 tiles per m²), the Redland 49 (a large format tile at roughly 10 tiles per m²), and traditional plain tiles which require around 60 tiles per m² due to their smaller size and double-lap fixing. Our roof tile calculator accounts for tile type, roof area, and wastage to give an accurate order quantity.

Under UK Building Regulations (Approved Document C), roofs must prevent moisture ingress and provide adequate ventilation. Roofing underlay (breathable membrane) must comply with BS 5250, and battens are typically 25mm × 50mm treated softwood fixed at gauge spacings specified by the tile manufacturer. The felt and batten calculator works out underlay rolls and batten linear metres based on your roof area and tile gauge. Ridge tiles, dry ridge systems (now increasingly specified over traditional mortar bedding), hip tiles, and valley troughs must also be quantified for a complete roofing order.

Flat roofs in the UK are regulated under Approved Document C and must achieve a minimum fall of 1:80 (with 1:40 being the recommended design fall to allow for construction tolerances). Common flat roof covering systems include EPDM rubber membrane (such as ClassicBond or Firestone), GRP fibreglass (Fibreglass Flat Roofing from Topseal or Cure It), and torch-on felt (SBS modified bitumen). Our flat roof membrane calculator helps estimate the membrane area, insulation, and trims needed for flat roof projects.

Lead work remains essential in UK roofing, particularly for flashings at abutments, chimneys, valleys, and dormer cheeks. Lead sheet is specified by code number (Code 3 to Code 8) with Code 4 being the most common for flashings and Code 5 for valleys. All lead work should follow the Lead Sheet Association guidelines and be installed by competent roofers to ensure longevity and weather-tightness.