Whole-life costs: Concrete vs steel | Features

A - Base building: Steel-framed, air-conditioned office
Basic information
Gross internal floor area:	11,700 m²
Form:	Six storeys high and 15 m deep on plan
Construction:	Steel frame of 44 kg/m²
Substructure:	200 mm groundbearing slab, bearing on to 2.5 m deep pad foundations
Roof:	Flat, Sarna single-membrane proprietary roofing system with parapets
External walls:	Mostly wall cladding with reconstituted stone. Ten per cent is polyester powder coated aluminium curtain-walling, fully glazed to clear height with double-glazed low-emissivity glass
Window frames:	Aluminium for about 60% of clear height
Windows:	Double-glazed, low-emissivity glass
Air-conditioning:	Chilled beams with displacement ventilation in a raised floor plenum of 400 mm deep
Lifts:	Three passenger and one goods

Capital costs (£) (excluding fees)
Substructure	£544,010
Structure	£2,013,435
External envelope	£3,090,609
Internal divisions	£528,842
Finishings and fittings	£2,805,140
Mechanical	£3,707,744
Electrical and communications	£2,486,371
Lifts	£594,093
Preliminaries, overheads and profit	£2,680,646
Design and construction contingency @ 8%	£1,475,933
Total	£19,925,000

Annual energy consumption (£)
Space heating	£9,457
Cooling and fans	£32,872
Lighting	£14,165
Other energy costs	£35,194
Total (over 30-year period)	£91,688

D - Environmental impact
		CO2 output		Ecopoints
	Quantity	Rating	Tonnes	Rating	Total
Steel frame with composite floors
Pad foundations	263 m³	0.31	81.53	5.3	1,393.90
Steel frame	515 t	0.76	391.4	11	5,665.00
Note: The above ratings accept the steel industry’s calculation methodology (previously questioned)
Hot-dip galvanized steel permanent formwork	9.215 t	1.34	12.35	11	101.37
140 mm lightly reinforced concrete	1290 m³	0.37	477.3	5.3	6,837.00

Total for steel frame option excluding operation			963		13,997
CO2 produced over 30 years	30 years	775	23,250

CO2 total emissions for steel frame option including operation			24,213

Insitu concrete frame and floors
Pad foundations	440 m³	0.31	136.4	5.3	2,332.00
Reinforced concrete columns	323 m³	0.38	122.74	5.3	1,711.90
Reinforced concrete beams	59 m³	0.38	22.42	5.3	312.7
(Taken to perimeter, but can be avoided)
Reinforced concrete floors	2675 m³	0.38	1,016.50	5.3	14,177.50

Saving 200 mm wall height per level (approx)	–341 m²	0.1	-34.1	1.1	–375.10

Total for insitu concrete option excluding operation			1,264		18,159
CO2 produced over 30 years	30 years	718	21,540		N/A

CO2 total emissions for insitu concrete option including operation		22,804

Summary of changes

Overall extra for concrete option excluding building operation		301 (up 31%)		4,162 (up 30%)

Overall saving for concrete option including building operation	1,409 (a 6% saving on total energy costs)