How Much Insulation for a 30x40 Shop?
Bags or rolls
10 bags
The four walls of a 30 by 40 shop at 8 foot plate height, 140 linear feet of wall, framed at 16 inches on center.
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How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Wall or ceiling area1120 sq ft
- Stud or joist spacing16 in
- Coverage per bag or roll106.8 sq ft
Bags or rolls10 bags
| Gross area | 1,120 sq ft |
|---|---|
| Framing factor at 16 in oc | 90% |
| Cavity area to insulate | 1,008 sq ft |
| Bags at 106.8 sq ft | 10 |
| Coverage bought | 1,068 sq ft |
The material list this produces
| Insulation batts, bags | 10 |
|---|---|
| Vapor retarder, sq ft (if required) | 1,120 |
Coverage per bag compared
Bag coverage is the number that decides this, and it is printed on the bag. Here is the same area at five coverages, from 40 square feet a bag up to the 106.8 default.
| Coverage per bag | Bags or rolls | Coverage bought |
|---|---|---|
| 40 sq ft | 26 bags | 1,040 sq ft |
| 50 sq ft | 21 bags | 1,050 sq ft |
| 75 sq ft | 14 bags | 1,050 sq ft |
| 90 sq ft | 12 bags | 1,080 sq ft |
| 106.8 sq ft | 10 bags | 1,068 sq ft |
What else matters here
A hundred and forty feet of wall at eight feet is 1,120 square feet gross, 1,008 of cavity, ten bags.
What this calculator assumes
- Framing takes up roughly 10 percent of a wall at 16 inch on center and 7 percent at 24. Cavity area is reduced accordingly, so you do not buy insulation for the studs.
- Bag coverage varies a lot by R value and width. The default is a common R-13 kraft faced batt bag; read your own bag and change it.
Questions people ask
How many bags of insulation for a 30x40 shop?
Ten bags for the four walls at 8 foot plates, based on 1,120 square feet of wall and 1,008 of cavity.
The insulation calculator takes any dimensions you like and hands back the same list.
Other common sizes
23 more sizes are answered on the insulation calculator page