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R-49 is the common target for the roof or ceiling in cold and mixed climates. That is about 20 inches of blown fibreglass, 15 inches of blown cellulose, 16 inches of fibreglass batt or about 8 inches of closed-cell spray foam. Air seal the ceiling plane before adding any of it.
Radiant barrier reflects summer heat back out of the roof deck. It shines in hot climates. Enter your attic footprint and roof pitch for roll counts and savings.
With these inputs:
| Result | Value |
|---|---|
| Roof deck area to cover | 1,478 sq ft |
| Rolls required | 3 rolls |
| Staples estimate | 370 staples |
| Material cost | $325 |
| Expected cooling savings | 12% |
| Best value verdict | Strong payback |
Roof deck area = attic floor area × pitch multiplier · Rolls = deck area ÷ (roll width × roll length) · Savings % depends on climate zone — hot zones benefit most
Barely. It reflects summer heat gain, so payback is real in zones 1 to 3 and marginal from zone 5 north. Cold-climate money is better spent on attic depth and air sealing.
Stapled to the underside of the rafters is standard — laying it on top of insulation collects dust, which kills reflectivity within a few years.
Material is about $0.22 per sq ft of roof deck for perforated foil. A 1,500 sq ft attic at a typical 1.12 roof-slope factor has about 1,680 sq ft of deck, so roughly $370 of foil plus staples. Labor is the bigger variable: stapling to rafters in a tight attic is slow, awkward work, which is why installed quotes run several times the material price.
In hot sunny climates with ducts in the attic, it can make a measurable difference by reflecting radiant heat off the roof deck. In cold climates it does very little, because the dominant heat flow is conductive rather than radiant. It is a climate-dependent product being sold as a universal one, which is where most of the disappointment comes from.
Yes, and this is the thing most installations get wrong. A reflective surface in contact with another material conducts through the contact instead of reflecting across a gap. Laid straight onto existing insulation, a radiant barrier does almost nothing — it needs an air space facing it to function at all.
No. It addresses one of three heat transfer paths and does nothing about conduction through the ceiling. It is an addition to attic insulation in the right climate, not a substitute for depth, and any product marketed as replacing R-value should be treated with suspicion.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.