Floor Insulation Calculator
Calculate U-values for suspended timber floors and solid concrete floors. Our calculator helps you determine the right thickness of insulation to meet Building Regulations Part L targets of 0.22 W/m2K for extensions.
U-Value Calculator
Check Part L 2021 compliance for your insulation project
Tips for Floor Insulation
- Suspended timber floors need ventilation - never block airbricks
- Use rigid boards for solid floors, mineral wool between joists for suspended
- Consider moisture barrier for solid floor insulation
- Insulating floors typically saves 5-10% on heating bills
Floor Insulation Cost Estimates
| Floor Area | Suspended | Solid Retrofit | Property |
|---|---|---|---|
| 20m2 | GBP 400-600 | GBP 800-1200 | Single room |
| 40m2 | GBP 800-1200 | GBP 1600-2400 | Ground floor flat |
| 60m2 | GBP 1200-1800 | GBP 2400-3600 | Terrace house |
| 80m2 | GBP 1600-2400 | GBP 3200-4800 | Semi-detached |
Common Mistakes to Avoid
Blocking underfloor ventilation
Problem: Timber rot and structural damage
Solution: Maintain all airbricks and cross-ventilation pathways
Wrong insulation type
Problem: Compression, moisture damage, poor performance
Solution: Use rigid for solid floors, flexible for between joists
No vapour barrier
Problem: Moisture migrating into insulation
Solution: Install DPM on warm side for solid floors
Gaps around pipes
Problem: Cold bridges and heat loss
Solution: Cut insulation carefully around all services
Compressing insulation
Problem: Reduces R-value significantly
Solution: Maintain full thickness - add support netting if needed
Understanding Floor Insulation
Floor insulation prevents heat loss to the ground or to unheated spaces below. Suspended timber floors allow insulation between joists, while solid concrete floors require insulation above the slab, raising floor levels.
For complete home insulation, combine floor work with loft insulation and wall insulation for maximum energy savings.
Example: 40m2 Suspended Floor
Before: Uninsulated timber floor (U-value approx 0.7)
After: 100mm mineral wool between joists (U-value approx 0.25)
Cost: GBP 800-1200 installed
Annual saving: GBP 60-100
Frequently Asked Questions
Related Calculators
Other Calculators
Need Professional Advice?
Get in touch for custom calculations or project guidance.