How Much Insulation for 2,500 Square Feet?
Bags or rolls
22 bags
2,500 square feet of wall or ceiling, framed at 16 inches on center, with 106.8 square foot bags.
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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 area2500 sq ft
- Stud or joist spacing16 in
- Coverage per bag or roll106.8 sq ft
Bags or rolls22 bags
| Gross area | 2,500 sq ft |
|---|---|
| Framing factor at 16 in oc | 90% |
| Cavity area to insulate | 2,250 sq ft |
| Bags at 106.8 sq ft | 22 |
| Coverage bought | 2,350 sq ft |
The material list this produces
| Insulation batts, bags | 22 |
|---|---|
| Vapor retarder, sq ft (if required) | 2,500 |
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 common coverages.
| Coverage per bag | Bags or rolls | Coverage bought |
|---|---|---|
| 40 sq ft | 57 bags | 2,280 sq ft |
| 50 sq ft | 45 bags | 2,250 sq ft |
| 75 sq ft | 30 bags | 2,250 sq ft |
| 90 sq ft | 25 bags | 2,250 sq ft |
| 106.8 sq ft | 22 bags | 2,350 sq ft |
What else matters here
Twenty five hundred square feet gross, 2,250 of cavity, twenty two bags. That is a whole house of walls, or the ceiling of a large one.
If it is a ceiling, the R value is much higher than a wall's and the reason is that heat rises and the attic is the cheapest place in the building to add depth. Current energy code ceiling values run around R-38 in the warmest zones and R-49 to R-60 further north, against R-13 to R-20 for the walls. Nowhere else in the house does another few inches of material cost so little.
That is also why an under insulated attic is the first thing any energy audit finds. Going from R-19 to R-49 in an attic is usually a one day job on a house this size, needs no drywall touched, and pays back faster than anything else on the list.
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 2,500 square feet?
Twenty two bags at 106.8 square feet per bag, covering the 2,250 square feet of cavity left after framing.
What R value should an attic have?
Roughly R-38 in the warmest zones and R-49 to R-60 further north, which is far more than a wall gets because depth is cheap in an attic.
Why do ceilings need more insulation than walls?
Heat rises, so the ceiling is the biggest loss path, and an attic has unlimited depth available. Adding inches there is the cheapest R value in the building.
The insulation calculator takes any dimensions you like and hands back the same list.