The following shows difference in prices and µ-values of houses built with different insulation methods. Prices are for insulation and internal blocks, not including bricks and plasterboard as these would be identical in both builds (50 homes @ 120m² each would need 6000m² of blocks and insulation):
| Build 1 |
Brick outer leaf 50mm Celotex Board Celcon Block 3.6N 600kg/m³ Dot and Dab Inner |
| Celotex Boards | £3.35 per board covering 0.54m² | £37,222 |
| Celcon Block 3.6N | £9.95m² | £59,700 |
| Total | £96,922 |
The total cost does not include the extra wall ties and fittings for the cavity boards. Also does not account for any damage/waste for board cutting/shaping.
| Build 2 |
Brick outer leaf 100mm Grey EPS Bead Dense concrete block 7.3N Dot and Dab Inner |
| Grey EPS Bead | £7.94m² | £47,652 |
| Dense Concrete Block 7.3N | £4.70m² | £28,200 |
| Total | £75,852 |
Saving on materials would be £21,070 for this project, while getting a better thermal performance. µ-values calculations are detailed below.
Element type: Wall – Masonry – partial cavity fill
Calculation Method: BS EN ISO 6946
| Layer | d (mm) | λ layer | λ bridge | Fraction | R layer | R bridge | Description |
| 0.130 | Rsi | ||||||
| 1 | 12.5 | 0.210 | 0.060 | Plasterboard (standard wallboard) | |||
| 2 | 15 | R-value | 0.430 | 0.200 | 0.170 | 0.035 | Drylining – plaster dabs |
| 3 | 100 | 0.150 | 0.940 | 0.0670 | 0.667 | 0.106 | Celcon Block (600 kg/m³) – outer |
| 4 | 50 | 0.022 | 2.273 | Celotex 50mm | |||
| 5 | 50 | R-value | 0.180 | Cavity unventilated | |||
| 6 | 105 | 0.770 | 0.136 | Brick outer leaf | |||
| 0.040 | Rse | ||||||
| 333 mm (total wall thickness) |
3.655 | ||||||
Total resistance:
Upper limit: 3.584
Lower limit: 3.407
Ratio: 1.052
Average: 3.495 m²K/W
µ-value (uncorrected): 0.286
µ-value corrections:
| Air gaps in layer 4 | ΛU = 0.004 | (Level 1) |
| Wall ties in layer 4 | ΛU = 0.003 | (2.50 per m², 12.5 mm² cross-section, λ = 17.0) |
| Total ΛU | 0.007 | (2.5% of µ) |
µ-value (corrected): 0.286 (ΛU not added since it is less than 3% of µ)
µ-value (rounded): 0.29 W/m²K
Element type: Wall – Masonry – full cavity fill: injected
Calculation Method: BS EN ISO 6946
| Layer | d (mm) | λ layer | λ bridge | Fraction | R layer | R bridge | Description |
| 0.130 | Rsi | ||||||
| 1 | 12.5 | 0.210 | 0.060 | Plasterboard (standard wallboard) | |||
| 2 | 15 | R-value | 0.430 | 0.200 | 0.170 | 0.035 | Airspace / plaster dabs |
| 3 | 100 | 1.130 | 0.088 | Concrete block (dense) | |||
| 4 | 100 | 0.032 | 3.125 | Grey EPS Bead | |||
| 5 | 105 | 0.770 | 0.136 | Brick outer leaf | |||
| 0.040 | Rse | ||||||
| 333 mm (total wall thickness) |
3.749 | ||||||
Total resistance:
Upper limit: 3.722
Lower limit: 3.675
Ratio: 1.013
Average: 3.698 m²K/W
µ-value (uncorrected): 0.270
µ-value corrections:
| Wall ties in layer 4 | ΛU = 0.003 | (2.50 per m², 12.5 mm² cross-section, λ = 17.0) |
| Celcon Block 3.6N | £9.95m² | £59,700 |
µ-value (corrected): 0.270 (ΛU not added since it is less than 3% of µ)
µ-value (rounded): 0.27 W/m²K
British Plastics Federation