Lay out membrane rolls, flashing pieces and sealed joints

Roll dimensions describe the supplied material. Laps and details determine how much of it covers the work. Draw the proposed runs before converting a total area into roll count.

Compare gross and effective coverage

An illustrative 1 m × 20 m roll contains 20 m² gross. With a specified 0.1 m side lap, the simplified repeating effective width is 0.9 m and area is 18 m² before end laps or cuts. A 35 m² field needs at least two rolls by that simplified calculation, but the actual run lengths may require more.

Count the ends of flashing runs

Three illustrative flashing pieces each 2.4 m long, joined with two 0.15 m laps, cover 7.2 − 0.3 = 6.9 m of run. Subtract the number of actual joints, not a lap at every piece end indiscriminately. Corners and terminations may require additional pieces.

Calculate sealant from the filled profile

An illustrative 12 m rectangular joint, 8 mm wide and 5 mm deep, contains 480 mL. Cartridge count then uses the selected product volume and a separately justified allowance. The rectangular assumption may not match the specified bead shape.

Keep details authoritative

Lap widths, compatible sealants, primers and joint profiles must come from the chosen system and design. The example numbers are not installation requirements. Use quantity tools to check an established detail rather than inventing a detail to suit a convenient roll or cartridge count.

Found a measurement or calculation issue? Send the example and your correction.