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The best attic insulation is the one that reaches your target R-value in the space you have, without blocking the soffit vents that keep the roof deck dry. On an open attic floor that usually means topping up with blown-in or unfaced batts laid across the joists; in a cathedral ceiling or a finished attic it means high-density batts or foam between the rafters.
Below, each type is compared by what it is for and the one specification to read, and the depth you need is worked out with the same function as our insulation calculator — for a 1,200 sq ft attic going from R-19 to R-49.
Pros and cons describe each type from its specifications; this is not a hands-on product test. As an Amazon Associate we earn from qualifying purchases.
Best for: Topping up an open attic floor, laid across the existing joists. Check: The R-value and width on the bag — match 16 in or 24 in joist spacing.
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Best for: Rafter bays, knee walls and areas near chimneys and recessed lights rated for contact. Check: R-value per batt and whether it is sized for 16 in or 24 in framing.
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Best for: Hot, sunny climates where the attic holds ductwork. Check: Perforated (breathable) vs solid foil, and the emissivity figure.
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Best for: Attic hatch covers, knee-wall backs and the underside of rafters in finished attics. Check: R per inch and whether the facer is foil (radiant) or plain.
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Best for: Every vented attic before adding insulation near the eaves. Check: Width for your rafter spacing and length to clear the insulation depth.
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Best for: Air sealing top plates, wiring holes and plumbing penetrations before insulating. Check: Gap size on the can, and fire-block rating where codes require it.
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ENERGY STAR recommends R-49 to R-60 for an uninsulated attic in most of the northern half of the US (climate zones 4 to 8) and R-30 to R-60 in warmer zones; your local code sets the minimum for new work. If you already have some insulation, add only the difference. The insulation calculator does this; the example below uses the same function.
Worked example: A 1,200 sq ft attic floor from R-19 to R-49
Plan on roughly 9.1–12 inches of new insulation over the whole floor, depending on the material — and check the bag's own coverage chart before counting bags or rolls.
Depth matters at the eaves too: the roof slope leaves less room there, which is why baffles go in first. See the roof insulation guide for vapour retarders, and the attic ventilation calculator to check your soffit intake before covering anything.
| Location | Usual choice | Typical R per inch | Why |
|---|---|---|---|
| Open attic floor, top-up | Blown-in or unfaced batts across the joists | 2.5–3.7 | Covers the joists and fills around obstructions |
| Around the hatch | Rigid foam cover plus weatherstrip | 4–6.5 | The hatch is often the biggest single leak |
| Rafters in a finished attic | Mineral wool or high-density batts plus foam | 3.3–6.5 | Limited depth; needs the highest R per inch |
| Eaves | Rafter baffles, then insulation | — | Keeps soffit air flowing to the deck |
| Underside of the roof deck (hot climates) | Perforated radiant barrier | — | Blocks radiant heat, adds no R-value itself |
| Top plates and penetrations | Spray foam and caulk | — | Air sealing before insulating |
For an open attic floor, blown-in cellulose or fiberglass, or unfaced fiberglass batts laid across the joists, are the usual choices because they cover the joists and fill around obstructions. In a finished attic or cathedral ceiling, mineral wool or high-density batts combined with rigid foam give the most R-value in limited depth.
Blown-in fills around wiring, bracing and irregular joists with fewer gaps, which is why it is common for top-ups. Batts are easier to handle without a machine and work well when the joists are regular. Either reaches the same R-value if it is installed without gaps or compression.
ENERGY STAR recommends R-49 to R-60 for most of the northern US and R-30 to R-60 in warmer areas. Subtract what you have, divide by the product's R per inch, and the insulation calculator converts that into depth.
Yes, if the old insulation is dry and not contaminated. Use unfaced insulation for the new layer so you do not create a second vapour barrier, and seal air leaks first.
In a vented attic with soffit vents, yes. Baffles keep insulation from blocking the air path from the soffits to the roof deck, which prevents moisture and ice-dam problems.