Solve backwards
How much attic roof will my rolls of radiant barrier cover?
- 4 rollsThe example worked below
- Attic Radiant Barrier CalculatorEvery figure is its own
You have
How much radiant barrier foil?
Worked by the Attic Radiant Barrier Calculator at the settings below.
The settings it uses
What it will do
1,818 sq ft of roof deck
169 m²
One roof deck. Enough for a roof deck about 43 × 43 ft.
Or several. About 1 roof deck of the size the Attic Radiant Barrier Calculator opens on: a roof deck about 40 × 40 ft.
Check it forwards
- Roof Deck Area
- 1,818 sq ft
- It asks for
- 4 rolls
- You have
- 4 rolls
The Attic Radiant Barrier Calculator asks for 4 rolls at that size, and 5 rolls one step larger.
If you had more, or less
Around your amount
Each worked by the Attic Radiant Barrier Calculator at the same settings.
Half
2 rolls
909 sq ft
a roof deck about 30 × 30 ft
Yours
4 rolls
1,818 sq ft
a roof deck about 43 × 43 ft
Half as much again
6 rolls
2,727 sq ft
a roof deck about 52 × 52 ft
Double
8 rolls
3,636 sq ft
a roof deck about 60 × 60 ft
Common amounts
What each amount of radiant barrier foil covers
The sizes it is usually sold in, each worked by the Attic Radiant Barrier Calculator at the settings above.
| You have | It covers | As one roof deck | Average roof decks |
|---|---|---|---|
| 1 roll | 455 sq ft(42.2 m²) | a roof deck about 21.3 × 21.3 ft | under 1 |
| 2 rolls | 909 sq ft(84.5 m²) | a roof deck about 30 × 30 ft | under 1 |
| 4 rolls | 1,818 sq ft(169 m²) | a roof deck about 43 × 43 ft | 1 |
| 6 rolls | 2,727 sq ft(253 m²) | a roof deck about 52 × 52 ft | 1 |
Five hundred square feet a roll
The calculator counts a 4 by 125 foot roll (1.2 by 38 m) at 500 square feet (46 m²) and adds ten per cent to the area before dividing. Read backwards, one roll lines about 454.5 square feet (42.2 m²) of deck, and four rolls about 1,818 (169 m²). Radiant barrier also comes in wider and longer rolls, and in perforated and double-sided grades that do not all carry the same coverage, so divide by the figure printed on yours.
Measure the slope, not the floor
The area is used exactly as entered; nothing here turns an attic floor into the sloping rafter plane. At a 6/12 pitch the roof is about 12% larger than the floor beneath it, and at 12/12 about 41%, so an order taken off the floor falls short and the gap grows with the pitch. Gable ends, knee walls and dormer cheeks are extra area to measure and add if you are lining those as well.
The foil has to face an air space
This is a material count, not a performance figure. The reflective face only works looking into an open air space, and only while it stays clean — dust on the surface raises its emittance. Eave baffles and the ventilation path must stay clear behind it, an unperforated sheet acts as a vapour retarder, and clearances to recessed lights, flues and chimneys come from the maker and the adopted code.
How the answer is worked
Nothing here is a second formula. The Attic Radiant Barrier Calculator runs forwards — a size in, a quantity out — and this page grows its own starting roof deck 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.
Attic Radiant Barrier Calculator
runs it forwardsEstimate how many rolls of reflective radiant barrier foil you need for an attic roof deck.
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 roof deck does 4 rolls of radiant barrier foil cover?
- At the Attic Radiant Barrier Calculator's own settings, 1,818 sq ft (169 m²) — a roof deck about 43 × 43 ft. That is about 1 roof deck of the size the calculator opens on: a roof deck about 40 × 40 ft. Every figure follows the settings, which you can change in the calculator.
- How many square feet is a roll of radiant barrier?
- The calculator's standard roll is 4 by 125 feet, 500 square feet (46.5 m²). Other widths, lengths and grades are sold and not all carry the same coverage, so read the label. With the calculator's ten per cent for overlap and cutting, a 500 square foot roll lines about 454 square feet (42 m²) of roof deck.
- How many rolls of radiant barrier for a 1,500 square foot attic?
- Measured on the floor, 1,500 square feet (139 m²) plus ten per cent is 1,650, which is 4 rolls (3.3 rounded up). At a 6/12 pitch the deck itself is about 1,677 square feet (156 m²) — still 4 rolls, at 3.7 — but at 12/12 it is 5, and lining the gable ends adds more.
- Does radiant barrier replace attic insulation?
- No. It works by reflecting radiant heat across an air space rather than resisting conducted heat, and it is a supplement to insulation, not a substitute. The calculator gives no R-value, energy saving or temperature figure — whether foil helps depends on the climate, the air space and keeping its face clean.