Insulation Removal / Add-Over Calculator
Topping up existing insulation? Find how many inches to add to go from your current R to the target.
Calculator
Going from R-19 to R-49 means adding R-30 — about 8.57 inches at 3.50 R/inch. You can add unfaced insulation over existing (no second vapor retarder) — confirm the assembly and moisture detailing on the data sheet and local code.
Most attics do not need a tear-out — they need a top-up. If you already have some insulation, you only pay for the gap between what is there and your target. This tool takes your existing R, your target R and the R per inch of whatever you are adding, and returns the inches to add plus the new total.
The default tops a tired R-19 attic up to R-49 with cellulose.
Formula
added_R = target_R − existing_R
added_depth_in = added_R ÷ R_per_inch
new_total_R = existing_R + added_R
Worked example
R-19 up to R-49 with cellulose. Added R = 49 − 19 = 30. Added depth = 30 ÷ 3.5 = 8.57 in. New total = R-49. You add roughly 8.5″ on top of the existing — you do not re-buy the R-19 you already own.
Background & practice
Add unfaced over existing. When you top up, use unfaced loose-fill or unfaced batts — a second faced (vapor-retarder) layer can trap moisture between the two and cause condensation. The existing facing stays; the new layer breathes.
Estimate the existing R honestly. Measure the current depth and multiply by a realistic R/inch (old, compressed or settled insulation is lower than fresh). If it is damp, moldy or rodent-fouled, remove it instead — then this becomes a removal-and-replace job (see the cost tool).
Air-seal before you bury. Adding depth over unsealed top plates, can lights and chases just insulates the leaks. Seal penetrations first; the added inches work far harder over a tight ceiling.
Reference table
| Material | R per inch (labeled) | Inches for R-38 | Inches for R-49 | Field note |
|---|---|---|---|---|
| Fiberglass batt | R3.1–R3.4/in | 11.7 in | 15.1 in | Cheapest; watch gaps and compression |
| Blown fiberglass | R2.2–R2.7/in | 15.5 in | 20.0 in | Loose-fill; settles a little over time |
| Cellulose | R3.2–R3.8/in | 10.9 in | 14.0 in | Denser, less air movement; recycled paper |
| Mineral wool (Rockwool) | R3.0–R3.3/in | 12.1 in | 15.6 in | Fire and water resistant; good acoustics |
| Open-cell spray foam | R3.5–R3.7/in | 10.6 in | 13.6 in | Air-seals; needs more depth for R |
| Closed-cell spray foam | R6.0–R7.0/in | 5.8 in | 7.5 in | High R/inch; adds rigidity, low perm |
| Rigid EPS | R3.6–R4.2/in | 9.7 in | 12.6 in | Lowest-cost rigid board |
| Rigid XPS | R4.5–R5.0/in | 8.0 in | 10.3 in | Mid rigid board; moisture resistant |
| Rigid polyiso | R5.6–R6.5/in | 6.3 in | 8.1 in | Highest rigid R; drops in cold temps |
Labeled published planning typicals — confirm the rated R/inch on your product’s data sheet. Depth uses the band midpoint.