Roof & Attic Insulation Calculator — m, R-value, cost
How to use this calculator
Enter your attic floor area (length x width or custom area in m²), select insulation type and target R-value. If you have existing insulation, enter its depth and type. Results update instantly with bags/rolls, depth to add, vapor barrier, and ventilation baffles.
Insulation types — blown fiberglass (R-0.044 W/mK), blown cellulose (R-0.038 W/mK), batt fiberglass (R-0.040 W/mK), batt mineral wool (R-0.037 W/mK).
R-value — thermal resistance in m²·K/W. Higher is better.
Saved Calculations
| Time | Type | Area m² | Depth | R-Value | Qty | Cost |
|---|
How to Calculate Attic Insulation (Metric)
This calculator estimates insulation depth in centimeters, number of bags or rolls, and cost to reach your target thermal resistance (R-value in m²·K/W). Enter attic dimensions in meters or centimeters, select insulation type by thermal conductivity (λ), and set your target R-value.
Formulas
R = thickness (m) / λ (W/mK). Depth needed = (Target R − Existing R) × λ. Bags = Area / Coverage per bag at target depth. Coverage decreases with depth for blown products. Batt rolls are area / roll coverage.
Thermal Conductivity (λ) Values
Blown fiberglass: λ=0.044 W/mK. Blown cellulose: λ=0.038 W/mK. Batt fiberglass: λ=0.040 W/mK. Batt mineral wool: λ=0.037 W/mK. Lower λ = better insulator = less depth required.
FAQ
Can I mix insulation types? Yes, R-values are additive. Blown insulation works well over existing batts. Vapor barrier? In cold climates, install on the warm side of the insulation per EN 13788. In mild climates, consult local building codes.
