Contractor's Design Portion - Designing Buildings Wiki

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Contractor's design portion

The contractors designed portion (sometimes referred to as 'contractor's design portion' or CDP)

is associated with JCT construction contracts. It is an agreement for the contractor to design

specific parts ofthe works. The contractor may in turn sub-contract this design work to specialist

sub-contractors. This should not be confused with design and build contracts where the

contractor is appointed to design the whole of the works.

Until 2005, the JCT Standard Building Contract had a contractors designed portion supplement

for use where the appointed contractor was required to design specific parts of the works. This

provision has now beenincorporated into themain contract, but a separate sub-contractor design

agreement isavailable where the main contractor is to design specific parts of the works and a

sub-contractor is to design part or all of the sub-contract works. The JCT Intermediate Building

Contract still has a separate contractors design agreement, as well as a sub-contractor's design

agreement. The JCT Minor Works Contract has a with contractors design option and a separate

sub-contract with sub-contractors design.

Theclients requirements for contractor's design will generally be set out in the tender documents

as Employers Requirements in response to which the contractor will submit ContractorsProposals.

Contractors design may be used with a Pre-Construction Services Agreement or Pre-

Construction Services Agreement (Specialist) to provide early consultancy services to the

project before the main construction contract commences.

Often, the portion of design left to the contractor is the detailing work undertaken by specialist

manufactures and installers. The main contractor has responsibility for managing the

procurement of its specialist sub-contractors design in an orderly fashion and to an agreed

programme so it can be approved by the clients design team (who within their conditions of

engagement avoid liability for specialist design). The main contractor also has to ensure that

various specialist sub-contractors under its control co-ordinate their emerging designs with each

other. For instance the services sub-contractors need to know both the grid system and position

of fixings for a suspended ceiling and likewise the ceiling sub-contractor needs to know details of

plant above ceilings which require maintenance access. To carry out this management function

'design managers' have become a regular addition to the main contractors project staff.

The main contractor may be given the responsibility for ensuring that its sub-contractors design

is submitted for and obtains building regulations approval. The clients design team will usually

submit specialist design to the planning authorities when necessary to satisfy planning

conditions since it is generally the design teams responsibility to obtain full planning consent.

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Design consultants need to judge how far to take their design before handing over its completion

to specialists. Furthermore it must be made abundantly clear exactly what the specialist has to

design within the work section. A performance specification must describe quality both in terms

of function and form, bearing in mind that contractors tendering in competition will respond with

the cheapest option available to meet the specification. The use of a sub-contractor design

approval procedures to improve what was tendered has been the source of back door variations

and many contractual disputes in relation to cost and/or delay. On the other hand it is a waste of

designers resources and time to develop the design of systems that may or may not be used.

Closed specifications reduce options in the specialist market and this is not in the best interestsof the client.

It is sensible for the main tender documents to ask for a sub-contractor design programme to be

submitted by the main contractor within a certain period after the contract has been placed. This

should track specialist design, the approval process, manufacture and installation and fit into the

overall contract programme. It is reasonable for the design team to insist on an even workload of

sub-contractor drawing submittals so it can balance its resources in relation to the comment and

approval process.

The introduction of building information modelling (BIM) is likely to have a profound effect on

contractor's design. If at the time of the main contractor's appointment, a fully-integrated and

collaborative building model has been prepared, it is unlikely that this will simply be handed over

to the main contractor. The model is more likely to remain under the management of the client's

design team. Whoever is managing the model will be the party that has to manage the collective

input of specialist designers. The main contractors role in this process could therefore become

redundant, which is not satisfactory under the current terms of contractor's design agreements

because it effectively means the designers would be controlling activities of the main

contractors sub-contractors. However, the main contractor carries the risk of a fixed price and

meeting the contract completion date. For this and for programme reasons, contractor's design in

the way that we know it now could become a thing of the past. In any case the advent of BIM is

likely to alter the timing of the inclusion of specialist design so it takes place in the pre-

construction design stage rather than in the construction stage. Consequently the design team

will work on the design with specialists in the pre-construction stage and insist that the tendering

contractors adopt the specialist and its design as part of the tender offer. So the scope of

specialist work, its price and programme will be included within the main contractor's bid. The

main contractors tender documents will also give the main contractor the choice of seeking

alternative sub-contractors thus avoiding the legal problems associated with nominated sub-

contractors when the courts judged that a main contractor was not liable for the performance of a

sub-contractor forced upon it by the client or its agents.

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