Building envelopes account for up to £25bn a year in construction costs. In our latest specialist update, our expert team at Gardiner & Theobald examines the trends and costs in curtain walling, roofing and stone construction

01 — Overview

The envelope of a building typically accounts for 15-25% of the cost of the overall construction budget for a building, which adds up to a total of £15-25bn a year at current prices.

This market has grown recently and is set to continue for at least two years, although several significant recent changes are impacting on costs. The recent amendments to Part L of the Building Regulations demand higher-performing roofing and cladding and if architects insist on all glass buildings they will have to specify triple glazing. This will inevitably push up costs. Prices and lead times for bespoke cladding have increased due to the demise of Schmidlin, which has reduced competition at the top end of the market. This effect is likely to become more pronounced once the next generation of central London office blocks starts on-site.

Finally, cladding and roofing companies have been absorbing increased energy and raw material prices but pressure on margins means these costs are now being passed on.

Curtain walling

Duncan Smith reviews the cost of curtain walling and the impact of Schmidlin’s collapse on capacity in this high-risk but expanding market

02 — Market overview

The UK curtain walling market has a total estimated annual value of more than £600m. Enquiries have picked up significantly over the past year and growth has been in excess of 10% for the period.

The bulk of curtain walling in the UK is still consumed by commercial office developments and the current high demand in the commercial office market is predicted to continue for the next couple of years.

The Mercedes Benz museum in Stuttgart features highly complex cladding – the glazed area lines up with an internal ramp that spirals down around the perimeter of the building
The Mercedes Benz museum in Stuttgart features highly complex cladding – the glazed area lines up with an internal ramp that spirals down around the perimeter of the building

03 — Hot topic: Managing risk

Managing risk

The demise of Schmidlin has illustrated that bespoke curtain wall contracting can be a relatively high-risk market. This has led the high-end curtain walling market to improve their risk management procedures to reduce and control the levels of risk with contracts.

There is a clearer understanding within the industry that the level of risk should match the level of return and the curtain walling market will take a more balanced and selective approach when it is securing work.

Final negotiations will consider contract terms and conditions in parallel with the pricing levels – which will be higher in any case because of reduced competition.

Raw materials

The cost of raw materials has continued to rise; in particular aluminium, stainless steel and glass. Until recently, companies were attempting to absorb these increases in costs and maintain competitive pricing levels, but this led to great pressure on the profit margins, which were unsustainable in some cases. Therefore there has been an adjustment in the market to reinstate the margins to more realistic levels. This is particularly true of glass products, where availability of quality commercial supplies is already limited.

Part L

The new regulations give maximum flexibility to designers when selecting the means of compliance for carbon dioxide emissions for new buildings. This leads to closer working between the designers, with the early involvement of services engineers in conjunction with the cladding design.

Although the impact on the cladding design will be determined by the overall building design, the areas where potential additional costs will be encountered are:

  • Increase use of high-performance glazing units, including gas-filled cavities
  • Higher insulation standards for external fabric and glazing
  • Improved airtightness of external fabric
  • Fixed or motorised external shading
  • Double wall facades
  • Triple glazing.

04 — Lead times and costs

The current high level of demand for curtain walling in the UK coupled with reduction in capacity due to Schmidlin’s demise has led to an increase in lead-in times by as much as 50%.

This has caused clients with high-quality, technically demanding requirements to appoint a specialist contractor at a much earlier stage in order to secure production capacity and reduce the risk of a delay.

Pre-construction services agreements with specialist contractors are likely to become more prevalent.


Curtain walling can range in value significantly and the following costings are purely indicative. It is advisable to undertake market testing with those specialists seen as most appropriate to the project.

It is also critical that specific conditions such as site constraints, client expectations, designers’ intentions and performance requirements are considered when putting an overall price to a curtain walling system.

In a typical city centre office, building prices range from £550/m² for a simple low specification system to £900/m2 for a high-specification curtain wall.

Typical design options: approximate costs

Cost of each additional frit £15-20/m²
Extra over cost on system for faceting 10-15%
Extra over cost on system for single radius 60% minimum
Glass external fins, depending on profile £250-350/m
Aluminium external fins, depending on profile £100-200/m
Extra over cost of laminated glass in place of toughened £15-20/m²
Inter-cavity blinds (motorised tilt only, manual raise and lower) £50-60/m²
Additional layer of glazing (opening inwards for access to cavity) £90-120/m²

Miscellaneous items

Parapets £250-400/m
Penetrations through system £1500-2000 each
Single doors £3500 each
Double doors £6000 each
External soffits £400/m²
Interface with other elements ie stone £250/m
Secondary steelwork project specific


Phil Saunders reports on changes in this expanding sector, including the impact of the rising cost of labour, oil and steel-based roofing materials

05 — Market overview

Gardiner & Theobald’s research has shown that the UK roofing market continues to grow, with an estimated annual turnover of £1.9bn for 2006, up 20% from 2000 figures.

The market for copper roofing has also benefited over the past 18-24 months from a growing appreciation of its appearance and lengthy life expectancy. However, prices have recently risen more than 20% in line with the increase in raw material, which has also affected pipework and cable costs.

Steel-based roofing materials have enjoyed increased use in the past five years but prices have gone up 20-30% because of raw material price increases. It is difficult to tell whether this growth will continue in spite of this price increase. The roofing market is having to pass on above-inflation increases to contractors.

The Gardiner & Theobald tender price indices previously reported low price rises of 3-4% in 2004 and 2005 despite steel prices rising 20-30%. This can be attributed to the influx of labour from Eastern Europe, which has eased the labour shortage in the construction industry. The latest review reports rises above 5%.

Oil price increases have resulted in the higher transport cost for the industry. Most of these increases have been passed on to the consumer. The liquid roofing sector has been most hit by oil price rises as they use oil-based materials such as asphalt and bitumen. The cost of liquid roofing is likely to follow fluctuations in oil prices for the foreseeable future.

The striking roof of the Woodhorn Colliery Museum features this spectacular serrated roof structure symbolising coal-cutting machinery
The striking roof of the Woodhorn Colliery Museum features this spectacular serrated roof structure symbolising coal-cutting machinery

06 — Hot topic: Labour rates

Labour rates

Labour rates have jumped as part of the Construction Industry Joint Council working rule agreement. On 27 June 2005, new labour rates came into force giving a 10.1% increase to craft operatives with at least NVQ Level 2 and a 5.9% increase to adult general operatives and semi-skilled workers. It is too early to assess the impact on tender prices.


With the 2012 Olympics promising increased workload and tight timescales, labour shortages are likely to increase the roofing markets lead-in times. The demand for roofing materials suitable for stadiums and sports facilities is also likely to rise.

Bespoke design

The ever-increasing use of bespoke designs are making it hard for small and medium-sized contractors to compete with large roofing contractors, who can handle bespoke designs more easily. There have also been reports of roof failures caused by problems with designing and installing these bespoke roofs.


The recently revised Part L means more highly insulated and airtight roofs will be specified, which is likely to result in higher prices.

Green roofs are being more frequently specified in response to increasing concerns about the environment.

07 — Lead times

The average lead times for membrane and profiled roofing has remained static over the last quarter at nine weeks and 14 respectively. However, contractors are busier certainly than a year ago and are being more selective with the projects they tender and are having to turn away work in order to maintain lead-in periods. The table (right) shows current roof covering tender prices.

Typical current rate (London region, second quarter 2006) based on 400m² roof area

Single-ply membrane £/m² 85-100
Natural slate £/m² 135-170
Aluminium standing seam £/m² 75-95
Two-coat asphalt £/m² 135-170
High-performance bitumen felt £/m² 75-95
Stainless-steel standing seam £/m² 95-125
Clay tiles £/m² 55-75

This 250m diameter roof clads the largest indoor sports facility in the world. Called Aspire, it is located in Qatar and will host the 15th Asia Games in December
This 250m diameter roof clads the largest indoor sports facility in the world. Called Aspire, it is located in Qatar and will host the 15th Asia Games in December

Stone construction and restoration

Demand continues to be strong, with quarries and the commercial sector in London among the beneficiaries, writes David Harding

08 — Market overview

According to stonework conservation and restoration specialist Szerelmey the restoration and conservation market across the UK is very busy at the moment, and is the continuation of several years of growth.

Demand is particularly strong in the London commercial sector, and this trend looks set to continue, as there are a lot of enquires about potential jobs and requests for budget pricing.

This long-term increase in demand for restoration work has also helped UK quarries, as many planning authorities want to see materials used to match the existing buildings.

Stone cleaning has been affected by water restrictions in drought-affected areas. Although commercial cleaning had not been banned, many clients have not proceeded with the cleaning part of a project for the moment, but this will mean that it may impact on the market by increasing demand for cleaning work in the future.

Lead-in times are generally controlled by obtaining licences and consents, but it is fair to allow about four to six weeks on a large restoration project.

The time needed for new stone varies enormously depending on availability and finish, but after an initial design stage, generally a period of 12-16 weeks is allowed for manufacture and production.

09 — Costs

Stone cleaning

The cleaning and repair of buildings is a specialist procedure given the variable nature of stone and its response to the localised environment, which means that a standard approach is often not possible.

The following details the most common methods of stone cleaning in the current marketplace, with typical specialist costs (excluding access scaffolding) based upon a contract valued at £250,000-£500,000 and measured to overall facade – that is, including windows.

Budget costs

Washing £4.50/m²–£10.00/m² (dependent on method)
Controlled air abrasion £11/m²-£19/m²
Poultices £30/m²-£100/m²
Chemical cleaning £6.50/m²-£13.00/m²

Treatment by lasers is used where a high degree of control is required on sensitive materials (such as statues), but this method does not appear to provide cost-effective cleaning of substantial areas, and specialist advice should be sought for budgetary purposes.

Stonework repairs

Typical specialist costs (excluding access scaffolding) based upon a contract valued at between £250,000-£500,000 are as follows:

• Masonry indent repair (patching)

This method should be used if pieces of stone are not available or the size of the area is less than 25mm deep.

Costs in the order of £17.50-£35 per 200mm × 200mm patch size in a plain stone and £37.50-£55 in a moulded stone.

• Masonry indent repair (filling and patching)

As above, but where the void is greater than 25mm a suitable filler should be used to build up the void until a suitable level for patching has been achieved.

Cost in the order of £27.50-£40 per 200mm × 200mm area with depth not exceeding 50mm in a plain stone and £45-£65 in a moulded stone.

It should be noted that neither of the above methods should be used on listed or existing historic buildings without prior approval or consent from a conservation adviser.

• Bonding

Cost in the order of £30 per piece in a plain stone and up to £130 in a moulded stone.

• Stitching

Where cracked or broken stones on a building can be jointed together. Cost in the order of £35-£65 per 300mm stainless steel dowel including grouting in a plain stone and £55-£85 in a moulded stone.

• Pinning

An alternative to stitching. A diagonal hole is drilled through the stone into the support medium behind and dowels can be inserted to provide restraint. The hole is then filled with an epoxy resin adhesive.

Cost in the order of £30 per piece for a plain stone and £40 for a moulded stone.

The above descriptions reflect options available for the repair of small areas of stone. The nature of this work means that in some instances indicative costs are not available and therefore specialist advice should always be sought.

Replacement stone

Example costs based upon a typical contract valued between £250,000-£500,000 would be as follows:

Portland stone:

600 x 300 x 100mm £150-350 per piece
Continuous moulded stone £450-750/m


600 x 300 x 100mm £250-550 per piece
Continuous moulded stone £825-1,900/m

Working of stone

Planing stone up to £130/hr
Sawing stone £50/hr
Masons £35/hr