How Much Insulation Do I Need?

R-value measures resistance to heat flow — higher means better insulation, but it also means a thicker batt that needs a matching stud or joist cavity. R-13 batts fit standard 2×4 wall framing; R-19 needs 2×6 framing; attics typically use R-30 to R-38 depending on your climate zone.

Using a wall-rated batt (R-13) in an attic falls short of most building codes, and compressing a thicker batt into a shallower cavity actually reduces its effective R-value — so matching R-value to the actual cavity depth matters more than buying the highest number available.

The Insulation Calculator converts your area and R-value choice into a bag count directly.

Faced batts (with a paper or foil vapor barrier attached) and unfaced batts aren't interchangeable in every application — faced batts go on exterior walls and ceilings below an unconditioned attic, while unfaced batts are typically used for interior sound-dampening walls or where a separate vapor barrier is installed.