Deck Waterproofing Calculator

Membrane system for occupied space below decks.

Deck length (ft)

Deck width (ft)

System (1=liquid, 2=sheet, 3=fiberglass)

Number of post penetrations

Wall contact length (ft)

Deck slope (%)

Tab to move between fields

Total waterproof area (sq ft)

317

Deck surface area (sq ft)240

Primer (gallons)2

Base coat / membrane (gal or rolls)11

Top coat (gallons)4

Sealant tubes17

Estimated material cost ($)$1,151.00

How to Use This Calculator

Enter Deck Length (ft) and Deck Width (ft) — the interior dimensions of the deck surface to waterproof.
Select System Type (1=liquid polyurethane, 2=peel-and-stick sheet membrane, 3=fiberglass/resin).
Enter Number of Post Penetrations and Wall Contact Length (ft) requiring counter-flashing treatment.
Set Deck Slope (%) — code minimum is typically 2% (1/4 inch per foot) for positive drainage.
Review Total Waterproof Area (sq ft), Primer Gallons, Base Coat/Membrane, and Top Coat Gallons to build your material order.
Use Sealant Tubes count and Estimated Material Cost for bid preparation and procurement.

How the result changes with Deck length (ft)

Deck length (ft): Length of the deck surface to waterproof.
Deck width (ft): Width of the deck surface to waterproof.
System (1=liquid, 2=sheet, 3=fiberglass): 1 = Liquid polyurethane (most common). 2 = Peel-and-stick sheet membrane. 3 = Fiberglass/resin system.
Number of post penetrations: Posts, railing bases, or other penetrations requiring flashing.
Wall contact length (ft): Linear feet where deck meets a wall requiring counter-flashing.
Deck slope (%): Slope for drainage. Code minimum is typically 2% (1/4 inch per foot).

Total waterproof area (sq ft): Total area including flashings, edges, and 10% waste.
Deck surface area (sq ft): Sloped deck surface area.
Primer (gallons): Primer gallons needed for substrate preparation.
Base coat / membrane (gal or rolls): Main waterproofing material quantity.
Top coat (gallons): Traffic-rated top coat for UV and wear protection.
Sealant tubes: Polyurethane sealant for penetrations and edges.
Estimated material cost ($): Approximate material cost.

Identify Input Parameters
4 parameters
Deck length (ft) = 20, Deck width (ft) = 12, System (1=liquid, 2=sheet, 3=fiberglass) = 1, Number of post penetrations = 6 = 6 input(s) provided
Calculate Total waterproof area
Total waterproof area = totalWaterproofArea * 1.10
317 = 317
Calculate Deck surface area
240 = 240
Calculate Primer
Primer
2 = 2