CALC-N-001 · DRAWING NO. IN-001 · REV A
Insulation calculator.
Drafted to scale · cited sources · honest numbers
Select the insulation type and target R-value. The calculator returns depth, bag count (blown), board feet (spray foam), or coverage area (batt), with a material-cost range. Cellulose shows both installed and settled depth. Fires IRC R806.5 and R316 code warnings.
◈ DRAFTING PANEL · INSULATION TAKEOFF · N.T.S.
SHEET IN-001 · REV A
Redline · scope notice Material takeoff only. Does not evaluate vapor barriers, air sealing, ventilation baffles, or flash-and-batt minimum closed-cell depths by climate zone. Blown and spray quantities assume open cavity with no obstructions. Batt output is coverage area only; check manufacturer packaging for pieces per bag.
Note 01 · Field Procedure
How to measure for insulation
- For attics: measure the exterior footprint of the house (length x width). Subtract overhangs if the attic floor does not extend past the exterior wall line. The attic floor area is the insulation area.
- For walls: measure each wall height and length. Subtract window and door openings. The net wall area is the insulation area. Standard stud cavities are 3.5 in. deep (2x4) or 5.5 in. deep (2x6).
- Check existing insulation. Push a ruler through the material to the ceiling deck. Subtract existing R-value from the target. Blowing over existing batt insulation is common in attic upgrades.
- Determine whether the attic is vented or unvented. Vented attics have soffit and ridge vents. Unvented (hot roof) assemblies require air-impermeable insulation per IRC R806.5.
Note 02 · Equation
The formula
depth = Rtarget ÷ R/in
R_targettarget R-value (from IECC by climate zone)
R/inR-value per inch for the insulation type
depthinches of insulation needed
Cellulose: depth shown is installed (pre-settlement). Settled depth = installed x 0.82. Bag count uses installed depth.
Note 03 · Sanity Ranges
Insulation by project
| T | Use case | Notes |
|---|---|---|
| 600 sf | Small attic / cape cod | Cellulose R-49: ~26 bags. Half-day job with a blower rental. |
| 1,200 sf | Standard ranch attic | Cellulose R-49: ~52 bags. The most common DIY blown-in job. |
| 2,000 sf | Large attic / colonial | Cellulose R-49: ~86 bags. Budget a full day plus helper. |
| 200 sf | Wall cavity section | R-13 batt: 200 sf material. Match batt width to stud spacing (15 in. or 23 in.). |
| 800 sf | Crawlspace floor | R-25 batt or spray foam. Crawlspace insulation often requires vapor barrier on top. |
Note 04 · References
Sources
Authorities cited on this sheet
- IECC 2021: International Energy Conservation Code · ICC. Defines minimum R-values by climate zone and location (attic, wall, floor). Table R402.1.2 is the residential insulation schedule. Basis for the zone selector and target R-value defaults.
- IRC R806.5: Unvented Attic and Unvented Enclosed Rafter Assemblies · IRC 2021 Chapter 8. Prohibits air-permeable insulation in unvented attic assemblies. Requires air-impermeable insulation (spray foam) or a flash-and-batt hybrid. Enforced as a hard warning in this calculator.
- GreenFiber Blown-In Cellulose Insulation · 30 lb bag coverage: ~40 sqft at 10 in. depth. Basis for the cellulose bag count and installed-depth math.
- Cellulose Insulation Manufacturers Association (CIMA) · Trade association for loose-fill cellulose. Publishes the ~18% settlement factor from installed to settled depth that drives the dual-depth display and the FTC Rule 460 labeling requirement.
- Insulation Institute (NAIMA) · North American Insulation Manufacturers Association. R-value per inch reference tables for fiberglass blown (2.2-2.7), batt (3.4-3.7), and general fiberglass guidance.
PROJ MATERIALFOREMAN
SHT IN-001 / 014
REV A · 2026-04-19
DRAWN MF