Solve backwards
How much wall will my fluid-applied weather barrier cover?
- 5 galThe example worked below
- Fluid-Applied Weather Barrier Coating Coverage CalculatorEvery figure is its own
You have
How much fluid-applied weather barrier?
That is 5 gal(18.9 L). Worked by the Fluid-Applied Weather Barrier Coating Coverage Calculator at the settings below.
The settings it uses
- Wet Film Thickness per Coat
- 0.03 in
- Number of Coats
- 2
- Width of the Detail Band
- 6 in
- Lap and Waste Allowance on Tape or Mesh (%)
- 10
What it will do
123 sq ft of sheathing
11.4 m²
One wall. Enough for a wall 15.3 ft long and 8 ft high.
Or several. Less than one wall of the size the Fluid-Applied Weather Barrier Coating Coverage Calculator opens on (a wall 135 ft long and 8 ft high).
Check it forwards
- Substrate Area to be Coated
- 123 sq ft
- Length of Joints and Details to be Treated
- 22.1 ft
- It asks for
- 5 gal
- You have
- 5 gal
The Fluid-Applied Weather Barrier Coating Coverage Calculator asks for 5 gal at that size.
If you had more, or less
Around your amount
Each worked by the Fluid-Applied Weather Barrier Coating Coverage Calculator at the same settings.
Half
2.5 gal
61.3 sq ft
a wall 7.7 ft long and 8 ft high
Yours
5 gal
123 sq ft
a wall 15.3 ft long and 8 ft high
Half as much again
7.5 gal
184 sq ft
a wall 23 ft long and 8 ft high
Double
10 gal
245 sq ft
a wall 30.7 ft long and 8 ft high
Common amounts
What each amount of fluid-applied weather barrier covers
The sizes it is usually sold in, each worked by the Fluid-Applied Weather Barrier Coating Coverage Calculator at the settings above.
| You have | It covers | As one wall | Average walls |
|---|---|---|---|
| 5 gal(18.9 L) | 123 sq ft(11.4 m²) | a wall 15.3 ft long and 8 ft high | under 1 |
| 10 gal(37.9 L) | 245 sq ft(22.8 m²) | a wall 30.7 ft long and 8 ft high | under 1 |
| 25 gal(94.6 L) | 613 sq ft(57 m²) | a wall 76.6 ft long and 8 ft high | under 1 |
| 55 gal(208.2 L) | 1,349 sq ft(125 m²) | a wall 169 ft long and 8 ft high | 1 |
A litre a square metre a millimetre
The arithmetic is exact: one millimetre of wet film over one square metre is one litre. Two passes of 0.8 mm are 1.6 L a square metre before the detail bands; at 30 mils wet a gallon coats about 53.5 square feet a pass. With the calculator's joints and openings in, five gallons coat about 123 square feet of sheathing, and 20 litres about 11.5 m² — a barrier goes a fraction as far as paint.
Thickness is the one to watch
Wet film thickness is the only variable anyone can get wrong while working, so check it with a wet film gauge as you go. US data sheets state it in mils — 30 mils is 0.76 mm — and some state a dry figure, which is smaller by the product's solids content; applying a dry figure as a wet one leaves the barrier short of the thickness it was tested at under ASTM E2570.
Detail bands run longer than they look
Every sheathing joint, corner, rough opening and transition gets a band of barrier wider than the tape or fabric bedded in it. The calculator scales that with the wall — 60 m of detail on 100 m², about 195 feet on 1,080 square feet — but a facade full of small openings has far more, and it is the item that runs short. Rough or absorbent sheathing drinks more on the first pass, and overspray is extra again.
How the answer is worked
Nothing here is a second formula. The Fluid-Applied Weather Barrier Coating Coverage Calculator runs forwards — a size in, a quantity out — and this page grows its own starting wall in proportion until the quantity it asks for is what you have. Where it rounds up to whole containers, the answer is the largest size before the next one would be needed.
Where the calculator adds an allowance for cuts or breakage when you order, the same allowance comes off here, because it is the same calculator: a stack you already own finishes less than its face value. Where it adds none, neither does this page — the settings beside the answer say which.
Fluid-Applied Weather Barrier Coating Coverage Calculator
runs it forwardsWork out how much fluid-applied barrier a substrate takes at the specified wet film build, and how much detail tape or mesh goes with it.
Work out what to buy insteadSolve backwards
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Solve backwards
Start from what is already in the yard
Paint, sheets, rolls, bags and pieces, each read the other way by the calculator that orders it.
The calculator's own figures
Nothing is estimated twice: the page runs the same calculator you would order with.
The largest size that fits
Where a calculator rounds up to whole containers, the answer stops before the next one.
Both unit systems
Gallons and litres, square feet and square metres, side by side.
Frequently asked questions
- How much sheathing does 5 gal of fluid-applied weather barrier cover?
- At the Fluid-Applied Weather Barrier Coating Coverage Calculator's own settings, 123 sq ft (11.4 m²) — a wall 15.3 ft long and 8 ft high. Every figure follows the settings, which you can change in the calculator.
- How much sheathing does 20 L of fluid-applied weather barrier cover?
- At the Fluid-Applied Weather Barrier Coating Coverage Calculator's own settings, 11.5 m² (123 sq ft) — a wall 4.8 m long and 2.4 m high. Every figure follows the settings, which you can change in the calculator.
- How many square feet does a gallon of fluid-applied WRB cover?
- It depends on the wet thickness the maker specifies. At 30 mils wet a gallon covers about 53.5 square feet (5 m²) in one pass, so about 27 square feet at the two passes the calculator carries, less the detail bands. At a lower specified build it goes proportionally further — use the data sheet's figure.
- What wet film thickness for a liquid weather barrier?
- Whatever the manufacturer specifies for that product; the calculator opens at 0.8 mm (about 31 mils) a pass, two passes. Barriers are evaluated under ASTM E2570 at the thickness the maker states, so that figure, checked with a wet film gauge during application, is the one the barrier has to reach.
- Does fluid-applied WRB need tape at the seams?
- Most systems bed a tape or reinforcing fabric in a wider band of barrier at sheathing joints, corners, openings and transitions, and the calculator counts that reinforcement separately, with ten per cent for laps and corner wraps. Flashing membranes, sill pans and penetration boots are separate products with their own coverage.