AECOM associate David Holmes looks at external works and drainage costs
Design and works for external areas can be complex and sensitive. Strength, durability, cost and future-proofing must be considered. Different sites rarely have the same requirements.
External areas must usually allow both pedestrian and vehicular access. Popular material types today include block paving and brick paviours, particularly for external areas of residential developments. They can be supplied in a wide variety of colours and finishes, which combined with different laying patterns can create a range of aesthetically pleasing finishes.
Concrete paving stones can be a cost effective alternative to traditional clay block pavers, especially if large numbers are required.
In industrial environments reinforced concrete is preferred for access roads and loading bays, often combined with brick paviours for turning areas which suffer the most wear and tear and can be more easily repaired. Tarmac can be used to cover large areas such as car parks, as it easily accommodates small settlements and can be used very quickly after laying.
Street furniture is probably the largest and most diverse category of external works. It is used to create an identity for an area and to create subtle themes in city centres. Street furniture layout is used to create strong visual effects. Benches, seats and so on are manufactured in a wide range of material and styles. Themes can be extended to include matching signage, planters, lamp-posts and litter bins.
The term ‘external works’ describes any works carried out to the external environment of a building project. These can provide functional and aesthetic features.
The following rates are based on the UK average and represent typical prices at 2017 Q4. Please note that prices can vary significantly depending on the exact specification
Housing cost models meeting minimum planning requirements or to maximize sales potential at economic cost. Soft landscaped space only space; planting: turf ratio’s as shown; planting sizes and densities as indicated; one tree of 18-20cm girth at one tree per 100m² overall external area; mulch and watering after planting
Landscaped area; turf and trees only ; imported topsoil to turf areas at 50mm thick 1,250 - 1,525
Landscaped area 70:30 turf to planted area with imported topsoil to turf areas at 50mm thick 2,160 - 2,615
Landscaped area 50:50 turf to planted area; imported topsoil to turf areas at 50mm thick 2,470 - 2,990
Science and office parks
Areas of denser landscaping with relaxation areas and larger planting schemes; generally more mature at implementation with larger trees; Planting schemes often with larger swathes of groundcovers to give graded views over landscaped areas; planting density and sizes generally of higher standard than housing. Soft landscaped space only. Space planting turf ratios as shown; planting sizes and densities as indicated; one tree of 25-30cm girth at one tree per 100m² overall external area; mulch and watering after planting
Landscaped area; 100% turf and trees only; imported topsoil to turf areas at 50mm thick 1,496 -1,811
Landscaped area 70:30 turf to planted area with imported topsoil to turf areas at 50mm thick 2,423 - 2,933
Landscaped area 50:50 turf to planted area; imported topsoil to turf areas at 50mm thick 2,708 - 3,278
Civic environments and streetscape
Civic and public areas in the current climate encompass higher quality surfaces for public access. Planting is generally larger. There is a need for furniture and lighting
Civic town centre area of paved open space; model area 500m²
General open area; one 30-35cm trees with root cell planting system every 400m²; Metal tree grid; One bench per 200m², one bin per 500m²; Granite kerb surround
Concrete slab paved 14,725 -17,825
Granite paved 17,100 - 20,700
Granite paved with stepped terraces. 3 steps of 10m long each in an area of 500m² 23,750 - 28,750
Living wall; Design and installation of planted modules with automatic irrigation systems
Fabric based systems; indicative area rates as shown
Wall up to 20m² / 50m² 682 - 775 / 539 - 613
Wall up to 100m² / 150m² 506 - 575 / 495 - 563
Parking; macadam base and wearing course, per bay 900 - 1100
Parking; Block paviours 80mm thick 78 - 90
Pedestrian areas; 100mm thick concrete 60 - 70
Modular grass concrete paving 100mm thick 65 - 75
Resin bonded 1mm - 3mm golden pea aggregate pathways 77- 90
Excavate inspection chamber; concrete base; half section pipework and benching
Precast concrete inspection chamber 600 × 400 × 900mm deep nr 510 - 620
Polypropylene inspection chamber: mini access chamber 600mm deep nr 330 - 375
Polypropylene inspection chamber: 475 mm dia × 900 mm deep; ductile iron cover with screw down lid
Excavate and lay 100 mm diameter upvc pipes over 1.0m deep 49 - 62
Excavate and lay 150 mm diameter clay pipes over 1.5m deep 86 - 110
Excavate and lay 300 mm diameter concrete pipes over 2.5m deep 160 - 205
Excavate and lay 150 mm diameter cast iron pipes over 1.5m deep 180 - 225
Road signs; reﬂected trafﬁc signs 0.25m² area on steel post/illuminated nr 130 -280
Lighting to estates’ pedestrian areas; 4m-6m columns with up to 70W lamps nr 250 - 300
400W High pressure sodium lighting to main roads; 12m-15m spacing nr 660 - 800
Benches; hardwood and precast concrete 1200 -1600
Litter bins bolted to ground: concrete / hardwood nr 200-240/200 - 245 cast iron / large aluminium nr 410 - 490/nr 610 - 640
Street planters: Supply and locate precast concrete planters; ﬁll with topsoil:
50 mm shingle and drainage mat; plant with 5 litre and 3 litre shrubs for instant effect;
700 mm dia. × 470 mm high; white exposed aggregate ﬁnish each 900 - 1100