Insulation Calculator

How much insulation you need has no answer without a location, so this starts from the IECC climate zone and the prescriptive R-value minimums in the 2018 energy code. Give an attic area, whatever R is already up there and the material going in, and it returns the R-value still needed, the depth that takes, the volume of material and a bag count if you read the coverage off the bag's chart; a second mode counts batts for a framed wall after deducting the openings, and a third just shows the whole code table for your zone. The per-inch figures are published ranges, so the depth is given as a band as well as a midpoint. Editions and local amendments differ and a retrofit is usually not held to new construction minimums, so the code your building department has adopted is the one that governs.

Calculator Type

Measurements In

Square feet, inches and R-value Square metres, millimetres and RSI

This moves every measurement on the form and in the answer together. The code targets are a US table either way, and are printed in both.

Works out how much R you still need, how deep the material has to go to get there, and how much of it that is.

Area to Cover (sq ft) *

Square feet, or square metres if you switched above.

Climate Zone

IECC climate zones. Your county has one; the building department or the IECC map will say which.

Insulation Already There

An R-value, or RSI if you switched above. Zero for bare joists. Old loose fill is often around R-2.5 an inch, or 0.065 W/mK, so measure the depth and ask the supplier what it is.

Material Going In

Coverage Per Bag at That Depth (sq ft), optional

Every bag of loose fill carries a chart of the area it covers at each installed depth. Read it off that chart and the bag count follows. Leave at zero to skip.

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Areas In

Square feet Square metres

This moves the two area boxes and every area in the answer. The batt sizes below stay what they are: real North American products on 16 and 24 inch framing centres, with their coverage reported in whichever unit you pick.

Net area after the openings, then the batt count at the size you are buying. Batts are sold by finished R-value, so pick the one printed on the bag.

Gross Wall or Ceiling Area (sq ft) *

Square feet, or square metres if you switched above.

Windows and Doors (sq ft)

In the same unit as the gross area above.

Batt R-Value

Framing Spacing

Batt Length

Waste Allowance (%)

Offcuts around windows, short bays and the odd ruined batt.

Climate Zone

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