Case study using grey EPS bead

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.

µ-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

µ-value for Build 2 is 0.27

Saving on materials would be £21,070 for this project, while getting a better thermal performance. µ-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

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

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

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