What is loose-fill insulation?
Loose-fill insulation (also called blown-in insulation) consists of small particles of fiber, foam, or mineral material blown or poured into place. Common materials include mineral wool (rock wool or glass wool), cellulose (recycled paper fiber), and EPS beads (expanded polystyrene). It is widely used in attics, floors, and wall cavities because it fills irregular spaces and achieves uniform coverage.
How do you calculate how many bags of insulation you need?
Each bag has a stated coverage at a reference depth (typically 10 cm). To find coverage at your target depth, scale it proportionally:
Coverage at depth = bag coverage × (10 / target thickness in cm)
Bags needed = ⌈ area / coverage at depth ⌉ (rounded up)
For example, if a bag covers 6.5 m² at 10 cm and you need 20 cm depth over 50 m²: coverage at 20 cm = 6.5 × (10/20) = 3.25 m²/bag. Bags needed = ⌈ 50 / 3.25 ⌉ = 16 bags.
What is the R-value formula for loose-fill insulation?
R-value (thermal resistance) is calculated from the thickness and the material's thermal conductivity (λ):
R = thickness (m) / λ (W/m·K)
Typical λ values: mineral wool ≈ 0.036, cellulose ≈ 0.040, EPS beads ≈ 0.035. A 20 cm layer of mineral wool gives R = 0.20 / 0.036 ≈ 5.56 m²·K/W. Use our length converter if your measurements are in feet or inches.
What are some loose-fill insulation calculation examples?
Attic floor, cellulose: 80 m², 25 cm depth, bag coverage 6.5 m² at 10 cm. Coverage at 25 cm = 6.5 × (10/25) = 2.6 m²/bag. Bags = ⌈ 80 / 2.6 ⌉ = 31 bags. R = 0.25 / 0.040 = 6.25 m²·K/W.
Floor cavity, mineral wool: 40 m², 15 cm depth. Coverage = 6.5 × (10/15) = 4.33 m²/bag. Bags = ⌈ 40 / 4.33 ⌉ = 10 bags. R = 0.15 / 0.036 ≈ 4.17 m²·K/W.
Does loose-fill insulation settle over time?
Yes — and accounting for settling is essential for long-term performance. Cellulose settles 15–20% of installed depth over time due to gravity and vibration. Mineral wool and EPS settle far less — typically 2–5%. To maintain your target R-value after settling, install extra depth upfront: add about 20% extra for cellulose, or 5% for mineral wool and EPS.
Settling example: targeting 25 cm of cellulose — install at 30 cm (25 × 1.20). Targeting 20 cm of mineral wool — install at 21 cm (20 × 1.05). This avoids the need for top-up bags later.
What is the difference between mineral wool, cellulose, and EPS beads?
Mineral wool (rock wool or glass wool) is non-combustible, moisture-resistant, and has good acoustic properties — λ ≈ 0.036. Cellulose is made from recycled paper, is eco-friendly, and treats well for fire resistance — λ ≈ 0.040. EPS beads (polystyrene granules) are very lightweight and moisture-resistant — λ ≈ 0.035. For equivalent R-values, EPS and mineral wool require slightly less thickness than cellulose. When budgeting your project, the mortgage calculator can help you plan financing for larger home renovation work.
What R-value do I need for attic insulation?
Recommended R-values depend on climate zone and building code. In Northern Europe, attic floors typically require R-7 to R-10 (roughly 25–35 cm of mineral wool or cellulose). Norwegian TEK17 targets R-7 to R-9 for roof insulation. Central European codes commonly require R-5 to R-7. In the US, DOE recommendations range from R-30 in warm climate zones to R-60 in cold zones 5–8. Always verify with your local building regulations, as minimum energy efficiency standards continue to increase. Planning a full renovation? Pair this calculator with the paint calculator to estimate all your material quantities at once.