How Much Radiant Barrier Do I Need?
Radiant barrier quantity should be based on the surface being covered. For a roof-rafter installation, that surface is larger than the house footprint because roof pitch and overhang both add area.
The four inputs that determine coverage
- House area under roof: Use the approximate footprint beneath the roof, including covered areas that will receive material.
- Roof pitch: A steeper roof has more sloped surface over the same horizontal footprint.
- Overhang: Eaves extend the roof beyond the exterior walls.
- Waste allowance: The Ra-flect estimator adds 10% for overlaps, cuts, and obstructions.
Square footage chooses quantity; framing chooses width
The lowest-cost roll combination is not always the easiest installation. A 17-inch roll is manageable around common 16-inch framing. A 25.5-inch roll suits many 24-inch layouts. A 51-inch roll covers open areas quickly but is heavier and often easier with two installers. Confirm the actual framing and attic access before adding the recommendation to the cart.
What the calculator includes
- Roof-slope factor from the selected pitch.
- Estimated area added by the roof overhang.
- Ten percent installation waste.
- An efficient combination of currently available LP or VB rolls.
- One-click addition of the recommended mix to the cart.
The estimate is intended for conventional roof shapes. Complex hips, valleys, dormers, additions, porches, and multiple roof elevations may require field measurements or a larger allowance.
Enter the footprint, pitch, and overhang to get a coverage target and roll combination.