Client and designer need to ensure that the contractor (and subcontractors) will use the selected recycled materials, whatever type of contract is being used. Yet the contractor should not be restricted to the extent of increased costs or delays to the programme, if particular materials are difficult to find or not readily available.

The use of reclaimed or recycled materials can be specified for particular parts of the construction. Or particular materials can be specified to contain a minimum percentage of post consumer waste. The contractor then has free choice in sourcing the material, as long as the specification is followed.

For example in the National Building Specification (NBS), clauses for proprietary reference specification are available for a wide range of products. Products that utilise recycled materials can be named in these clauses. For some recycled and reused materials (demolition materials, reclaimed bricks, stone etc.) clauses are included while for others (e.g. recycled aggregate for concrete) general guidance only is given due to lack of agreed testing and quality control standards.

Special clauses can be inserted requiring the use of reclaimed and recycled materials, and products made from recycled materials for particular parts of the construction, for example:

• If concrete block construction is used, the aggregate shall be post consumer waste or crushed recycled concrete
• External guttering, down pipes and water butts shall be made from 100% recycled plastic

Sub-contractors are normally required to adhere to what is required of the main contractor, so that no additional clauses should be necessary.