# Insulation Calculator

Calculate how much insulation you need for walls, attics, and floors. Get batt bundles, blown-in bags, or spray foam board feet.

## What this calculates

Proper insulation is one of the best investments in energy efficiency. This calculator helps you determine the right amount of fiberglass batts, blown-in cellulose, or spray foam for your project. Select the desired R-value and insulation type to get accurate material quantities.

## Inputs

- **Total Area to Insulate** (ft²) — min 0 — Total wall, ceiling, or floor area
- **Stud/Joist Spacing** — options: 16" on center (standard), 24" on center
- **Desired R-Value** — options: R-11 (2x4 wall, 3.5"), R-13 (2x4 wall, 3.5"), R-19 (2x6 wall, 5.5"), R-21 (2x6 wall, 5.5"), R-30 (attic floor, 9.5"), R-38 (attic floor, 12"), R-49 (attic floor, 16")
- **Insulation Type** — options: Fiberglass Batts, Blown-In (Cellulose), Spray Foam
- **Waste Factor** (%) — min 0, max 20 — 5-10% for open areas, 15% for areas with obstacles

## Outputs

- **Net Insulation Area** (ft²) — Area after accounting for framing (studs reduce area ~10%)
- **Batts/Rolls Needed** — formatted as text — Based on standard batt packages
- **Bags (Blown-In)** — formatted as text — 30-lb bags of cellulose insulation
- **Required Thickness** (in) — formatted as text
- **Area to Order For** (ft²) — Including waste factor

## Frequently Asked Questions

**Q: What R-value do I need?**

A: R-value requirements depend on climate zone and location in the home. For most US climates: exterior walls need R-13 to R-21, attic floors need R-30 to R-60, and floors over unheated spaces need R-19 to R-30. Check your local building code for specific requirements.

**Q: What is the difference between batt and blown-in insulation?**

A: Batt insulation comes in pre-cut rolls or panels that fit between studs. It is easier to install in new construction. Blown-in insulation is loose fill sprayed into cavities and is better for retrofitting existing walls and attics with irregular framing or obstructions.

**Q: Can I add insulation on top of existing insulation?**

A: Yes, you can layer insulation to increase R-value. Do not compress existing insulation as this reduces its effectiveness. For attics, simply lay new unfaced batts or blow in cellulose on top of the existing layer.

**Q: Should insulation have a vapor barrier?**

A: In cold climates, faced insulation (with kraft paper or foil) should have the vapor barrier facing the warm (interior) side. In hot/humid climates, the barrier faces outward. Never sandwich insulation between two vapor barriers as trapped moisture can cause mold.

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Source: https://vastcalc.com/calculators/construction/insulation
Category: Construction
Last updated: 2026-04-21