Vapor barrier calculator: rolls and square feet

One row per slab or room: its length, width and how many identical ones. Add the seam lap, the turn-up at the walls and your roll size: the calculation gives the area to cover, the poly to order with the laps and the rolls. In imperial or metric.

Units Feet Meters

Area 1

Lengthft

Widthft

Identical areas

Seam lap (overlap)inTypical value (IRC 2021, R506)

Turn-up at the walls (yours)in

Roll width (yours)ft

Roll length (yours)ft

Waste (%)%

Result

Fill in the fields to see the result.

A quick estimate, without the layout. The template handles the whole job: every slab and footing, the concrete and the base under it, the rooms and their floors, and totals by section.

Vapor barrier: what the codes and makers say (reference)

The minimums our templates cite, as read. The product and your local code have the last word.

	What the sources say
Under a concrete slab (US)	6 mil polyethylene vapor retarder, joints lapped at least 6 in (152 mm)
Under a slab on the ground (Canada)	A soil gas barrier, usually 0.15 mm (6 mil) polyethylene, with a radon rough-in
Under a floating floor over concrete	6 mil (0.15 mm) polyethylene, lapped about 8 in (200 mm)

Sources: IRC 2021, R506; NBC 2020, 9.13.4; Makers' guides, 6 mil poly

How it is calculated

Area = length x width x identical areas, added up over every row (the construction templates' vapour barrier under the slab). Turn-ups = 2 x (length + width) x turn-up height, for each area. Area to cover = area + turn-ups. Each strip covers the roll width less one lap: poly to order = area to cover x roll width / (roll width - lap) x (1 + waste). Rolls = poly to order / (roll width x roll length), rounded up to the roll: an estimate, the real layout decides the end laps and the cuts. The lap starts at the code's 6 in (152 mm); the turn-up, roll size and waste are yours.