Flat Roof Material Estimator (EPDM/TPO)

Flat roofing systems like EPDM (Ethylene Propylene Diene Monomer) and TPO (Thermoplastic Polyolefin) require precise material quantification to prevent mid-job shortages or excessive waste. Unlike sloped roofs, flat roofs often feature parapet walls - vertical extensions of the wall past the roofline - which significantly increase the surface area requiring membrane coverage. A standard calculation of L × W often results in a material shortage of 15% to 20%.

This tool addresses the complexities of commercial and residential low-slope roofing. It factors in base dimensions, vertical wall flashing (parapets), and industry-standard waste coefficients for overlaps and trimming. Correctly estimating adhesive is equally critical; running out of bonding adhesive while a membrane is open can compromise the system's waterproof integrity. This calculator outputs roll counts based on standard widths and specific adhesive buckets required for both the field (horizontal) and vertical surfaces.

The total membrane area A is calculated by summing the horizontal deck area and the vertical parapet area, then applying a waste factor w (typically 1.10). The parapet area considers the perimeter length P covered by walls and the height h of the wall rise.

Adhesive quantity Q_adh depends on the coverage rate R (sq ft per gallon). Note that contact adhesives are often applied to both surfaces, effectively halving the coverage.