The green cost code

Combined heat and power

Combined heat and power (CHP) has come a long way in recent years. The plant is now far smaller, more efficient and infinitely more reliable than ever before. CHP got a bad name 10 years ago when some professionals had their ‘fingers burned’ with poor CHP plant constantly breaking down and not delivering the efficiencies that were expected.

Gas-powered turbines produce electricity and the heat generated from the turbine action is used to heat or cool the building as required. This can result in greatly reduced energy use since heat and cooling are produced as a by-product of power generation. Other fuels such as biomass are possible, but less common.

Modern plant is efficient, compact, quiet and reliable. New companies have sprung up that provide CHP ‘solutions’. These companies install the CHP and associated plant and M&E systems at their own cost. They then manage the delivery of power, heating and cooling to buildings and are responsible for carrying out all maintenance over a period of 10-25 years after which the plant belongs to the client.

The client/tenant pays for what they use at a pre-negotiated rate which is cheaper than buying the equivalent power from the grid. Data cabling is also installed by the provider throughout the building to enable the use of digital energy meters. The client can use these cables to provide broadband services throughout their building – an attractive side benefit for residential or public-sector schemes.

Waste disposal

A huge impact of construction is the waste produced, which is still predominantly put into landfill sites.

With a little planning, many materials can be sent for reuse or recycling at zero cost to the client and contractor. For example, several schemes exist to reuse old carpet tiles in charity projects. Contractors must segregate tiles during strip-out and stack them for collection. With good management, there is no additional labour required and collections can be arranged at 24 hours notice. The collector charges a small fee to cover their logistics however this is cheaper or equal to the equivalent cost of bins or skips.

Old carpet tiles are then deep cleaned and sold at greatly reduced rates to charity projects. Tiles that are in very poor condition are recycled back into carpet.

The choice of waste contractor is also very important: some waste contractors can take away mixed bins or skips and segregate waste at their facilities for reuse or recycling – at no cost to the client or contractor. There is no change in practice on site with deliveries and collections of skips taking place as normal.

Timber

How many contractors or clients really know where their timber comes from? Not many. Timber is almost impossible to trace back to source unless it comes from a recognised, certified source. FSC (Forest Stewardship Council) is an internationally recognised scheme to certify sustainably grown and harvested timber products. Responsible purchasing reduces the trade in illegally logged timber that finances conflicts in countries such as Congo and threatens the habitat of endangered species such as the orang-utan in Indonesia.

For popular timber species, such as oak, beech and birch, FSC or PEFC (an alternative scheme) timber can be procured at the same cost as non-certified timber, but must be specifically requested when orders are placed. Again, some thought is required from designers so that very unusual or scarce timber is not specified. Even in this case some suppliers can provide astonishingly authentic copies of rare timbers using commonly available sustainable timber. There is a small premium for this, but it is still cheaper and more environmentally friendly than the real thing.

Many contractors still use plywood for many low-grade temporary applications on site such as ramps, hoarding and boxing-in. Ply is an expensive high-grade product that can easily be replaced with FSC-certified OSB (oriented strand board). This comes in several grades including a waterproof type for outdoor use, a high-strength board for load-bearing applications and a smooth faced board that can be painted and used internally in place of MDF. OSB is approximately £5/sheet cheaper than plywood.

Aggregates

On one of our projects, we are using secondary aggregates in place of virgin aggregate dredged from the sea bed.

Secondary aggregate is produced as a result of another industry, in this case granite from the mining of kaolin in south west England. Around St Austell, there are enormous ‘mountains’ of granite that have been produced from centuries of kaolin mining. This rock can be used as aggregate in structural concrete and obtain equal and better strength than virgin dredged aggregate.

Dredged aggregate is the predominant product used in structural concrete although some land-mined aggregate is also used. Both of these extraction techniques damage the environment, with sea dredging being controversial with environmentalists because of feared long-term impacts on marine ecosystems and coastal erosion.

The secondary granite is crushed and graded then transported by ship to the Thames. Secondary aggregate does not incur any aggregates levy (currently £1.60/tonne on sand, rock & gravel), so is attractive for projects which need large quantities of aggregate In our case, prices from suppliers proposing secondary aggregates were equal to those proposing virgin aggregates in readymix concrete.

In addition, we are using a mechanical crusher on our site to produce aggregate for access roads, the piling mat and landscaping from existing demolition materials. This is extremely cost-efficient as the raw material is free.