Cost model: City of London offices, Part L | Features

City office development Part L cost breakdown
	*element cost (or saving)*	*cost/m2 gfa £*	*% of total cost*
Part L (2002) compliant scheme Construction cost of base scheme	17,800,000	1,913.98
Shell and core 9,300 m2 @ 1,640
Category A fit out 6,375 m2 @ 400

Enhancements to scheme to comply with Part L 2005: Option 1 40% glazing
*External walls, windows and doors*	*81,400*	*8.75*
Extra over double glazed curtain walling; for solar-control glass; average U-value improvement from 2.2 to 2.0 1,300 m2 @ 40
Extra over paint-backed glazed panels for improved insulation; average U-value improvement from 0.35 to 0.27 1,960 m2 @ 15
Extra; increase airtightness to achieve 7 m3/hr/m2. No cost addition as standard is already achieved with unitised curtain wall 3,260 m2 @ nil
*Heat source, space heating, air treatment and ventilation*	*(174,500)*	*(18.76)*
Extra for; increased efficiency of condensing boilers to 89% 460kW @ 15
Saving for; reduced boiler capacity and pipework sizes due to improved facade performance and heat recovery; reduction of 350 kW (350)kW @ 275
Extra for: coefficient of performance for air cooled chillers increased to 3.1. No cost addition as chillers are typically specified to achieve this COP 806kW @ nil
Saving for; reduced chiller capacity and pipework sizes due to improved facade performance and heat recovery; reduction of 275 kW (275) kW @ 315
Saving for; reduced power loads to mechanical plant, reduced sizing of sub-mains distribution Item @ (5,000)
Extra for; allowance for heat recovery installation to air handling plant; run-around coils Item @ 6,500
*Builders’ work in connection*	*2,000*	*0.22*
Extra over costs of additional builders’ work in connection with heat recovery installation Item @ 2,000
*Preliminaries and contingencies*	*(18,900)*	*(2.03)*
Contractor’s overheads, site establishment and site supervision Allow 17% Item @ (13,900)
Contingency sum Allow 5% Item @ (5,000)

Construction cost – building only including costs of Part L compliance	17,690,000	1,902.16
Extra over costs of Part L compliance	(110,000)	(11.82)	(0.62)

Enhancements to scheme to comply with Part L 2005: Option 2 100% glazing, high performance glass, fixed louvres
*External walls, windows and doors*	*522,400*	*56.17*
Extra over double glazed curtain walling; high performance glass; average U-value improvement from 2.2 to 1.8 3,260 m2 @ 40
Extra; increase air tightness to achieve 7m3/hr/m2. No cost addition as standard is already achieved with unitised curtain wall 3,260 m2 @ nil
Extra; fixed external shading 2,450 m2 @ 160
*Heat source, space heating, air treatment and ventilation*	*(57,800)*	*(6.22)*
Extra for; increased efficiency of condensing boilers to 94% 470 kW @ 40
Saving for; reduced boiler capacity and pipework sizes due to improved facade performance and heat recovery; reduction of 340 kW (340) kW @ 275
Extra for: water cooled chillers in lieu of air cooled Item @ 10,000
Saving for; reduced chiller capacity and pipework sizes due to improved facade performance and heat recovery; reduction of 340 kW (340) kW @ 315
Extra for; distribution circuit to water cooled chiller; complete Item @ 100,000
Saving for; reduced power loads to mechanical plant, reduced sizing of sub-mains distribution Item @ (5,000)
Extra for; allowance for heat recovery installation to air handling plant; thermal wheel Item @ 19,000
*Builders’ work in connection*	*1,000*	*0.11*
Extra over costs of additional builders’ work in connection with heat recovery installation Item @ 1,000
*Preliminaries and contingencies*	*104,400*	*11.23*
Contractor’s overheads, site establishment and site supervision Allow 17% Item @ 81,000
Contingency sum Allow 5% Item @ 23,400

Construction cost – building only including costs of Part L compliance	18,370,000	1,975.27
Extra over costs of Part L compliance	570,000	61.29	3.20

Enhancements to scheme to comply with Part L 2005: Option 3 100% glazing
*External walls, windows and doors*	*735,000*	*79.03*
Extra over double glazed curtain walling; for low-e coating; average U-value improvement from 2.2 to 2.0; no additional cost as standard already achieved with curtain wall 3,260 m2 @ nil
Extra; increase air tightness to achieve 7m3/hr/m2. No cost addition as standard is already achieved with unitised curtain wall 3,260 m2 @ nil
Extra; motorised external shading 2,450 m2 @ 300
*Heat source, space heating, air treatment and ventilation*	*(57,800)*	*(6.22)*
Scope of works and costs as breakdown for Option 2
*Electrical installations*	*10,000*	*1.08*
Extra for; power supplies to motorised louvres 200 @ 50
*Special installations*	*50,000*	*5.38*
Extra for; control wiring to motorised louvres 100 @ 500
*Builder’s work in connection*	*4,000*	*0.43*
Extra over costs of additional builders’ work in connection with heat recovery installation and motorised louvres Item @ 4,000
*Preliminaries and contingencies*	*158,800*	*17.08*
Contractor’s overheads, site establishment and site supervision Allow 17% Item @ 121,800
Contingency sum Allow 5% Item @ 37,000

Construction cost – building only including costs of Part L compliance	18,700,000	2,010.76
Extra over costs of Part L Compliance	900,000	96.78	5.06

*External walls, windows and doors*	*551,300*	*59.28*
Extra; increase airtightness to achieve 7m3/hr/m2. No cost addition as standard is already achieved with unitised curtain wall 3,260 m2 @ nil
Extra over costs of; externally ventilated double wall facade with motorised blinds in lieu of standard unitised curtain wall; average U-value 1.60 2,450 m2 @ 225
*Heat source, space heating, air treatment and ventilation*	*(57,800)*	*(6.22)*
Scope of works and costs as breakdown for Option 2
*Electrical installations*	*10,000*	*1.08*
Extra for; power supplies to motorised louvres 200 @ 50
*Special installations*	*50,000*	*5.38*
Extra for; control wiring to motorised louvres 100 @ 500
*Builders’ work in connection*	*4,000*	*0.43*
Extra over costs of additional builders’ work in connection with heat recovery installation Item @ 4,000
*Preliminaries and contingencies*	*122,500*	*13.17*
Contractor’s overheads, site establishment and site supervision Allow 17% Item @ 94,500
Contingency sum Allow 5% Item @ 28,000

Construction cost – building only including costs of Part L compliance	18,480,000	1,987.10
Extra over costs of Part L compliance	680,000	73.12	3.82

Key performance criteria to meet Part L standards
General design criteria
Occupancy	8 m2/person
Outside air rate	10 l/s/person
Small power load	15 W/m2

*Option design criteria*	*Base*	*Option 1*	*Option 2*	*Option 3*	*Option 4*
	scheme	40%	100%	100 %	100%
	Part L	glazing	glazing, high	glazing,	glazing,
	(2002)	solar	performance	motorised	double wall
	compliant	control	glass, fixed	louvres	facade with
		glass	louvres		motorised
					louvres

Glass U-value (W/m2K)	2.20	2.00	1.80	2.00	1.60
Cladding U-value (W/m2K)	0.35	0.27
Heating load (kW)	810	460	470	470	470
Cooling load (kW)	1,080	806	740	740	740
Power (kW)	770	550	470	470	470
Solar heat gain	52%	42%	18%	18%	18%
Lighting load (w/m2)	13	12	12	12	12
Heat recovery;
run-around coils		50%
Heat recovery; thermal wheel			70%	70%	70%
Airtightness @ 50 Pa,
m3/hr/m2	10	7	7	7	7
Boiler efficiency	80.8%	89%	94%	94%	94%
Air cooled chiller
coefficient of performance	2.25	3.1
Water cooled chiller
coefficient of performance			4.0	4.0	4.0