Case Study using Grey EPS Bead

The following shows difference in prices and U 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.

U Value for Build 1 is 0.29

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

U Value for Build 2 is 0.27

Saving on materials would be £21,070 for this project, while getting a better thermal performance. U Values calculations are detailed below.

Build 1

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

U-value (uncorrected): 0.286

U-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 U)

U-value (corrected): 0.286 (ΛU not added since it is less than 3% of U)

U-value (rounded): 0.29 W/m2K


Build 2

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

U-value (uncorrected): 0.270

U-value corrections:

Wall ties in layer 4 ΛU = 0.003 (2.50 per m2, 12.5 mm2 cross-section,
λ = 17.0)
Total ΛU 0.003 (1.1% of U)

U-value (corrected): 0.270 (ΛU not added since it is less than 3% of U)

U-value (rounded): 0.27 W/m2K