Flashing Calculator

• Step flashing - Stepped pieces woven between tiles and up a wall or chimney side. One piece per tile course.
• Apron flashing - Single piece covering the front (downslope) face of a chimney or dormer.
• Back gutter - Behind a chimney or abutment, collecting water from the roof above. Requires an upstand and a gutter section.
• Valley flashing - Open valley between two roof slopes. Usually lead or aluminium.
• Abutment / wall flashing - Where a flat or pitched roof meets a vertical wall along its length.
• Ridge / hip cap - Lead or aluminium over a ridge or hip junction.
• Soaker - Small L-shaped pieces under step flashings at chimneys. Usually Code 3 lead or aluminium.

• Code 3 (1.32 mm · 14.97 kg/m²) - Soakers and small flashings
• Code 4 (1.80 mm · 20.41 kg/m²) - Step and cover flashings, most common
• Code 5 (2.24 mm · 25.40 kg/m²) - Valley gutters, back gutters, flat roofs
• Code 6 (2.65 mm · 30.05 kg/m²) - Parapet gutters, flat roofs, high-exposure locations

Lead is sold by weight (kg) or by roll. Always check current market price - lead is a commodity metal with fluctuating cost.

• Step / cover flashing - 150-200 mm wide (75 mm upstand + 75 mm cover)
• Apron flashing - 225-300 mm (minimum 150 mm upstand)
• Valley - 300-450 mm depending on pitch
• Back gutter - 300-450 mm (gutter width + upstand)
• Abutment - 150-225 mm (75 mm upstand minimum)
• Max individual lead piece length: 1500 mm (thermal movement)