What is the difference between design and construct and construct only?

Every building project has to answer one question early: who is responsible for the design?

The answer sets the delivery model. On public work, the two models that come up most are construct only and design and construct, often shortened to D&C.

Construct only

In construct only, the client engages architects and engineers to finish the design first. The contractor then prices the drawings and specifications and builds to them.

The client keeps full control of the design, and it also keeps the risk if the design is wrong or incomplete. Something missed in the drawings usually becomes a variation once it turns up on site. AS 4000 is a standard set of general conditions written for this model, and how variations are handled is covered in how variations are managed.

Design and construct

In design and construct, the client sets out what it needs, usually in a brief with performance requirements and sometimes a concept design. The contractor then develops the design, engages the designers and builds it.

One party carries both the design and the build. If a detail does not work on site, solving it is the contractor's job, not the client's. AS 4902 is the standard set of general conditions written for design and construct.

Where design and construct fits

D&C suits projects where the people who will use the building know exactly how they work and the brief can say so clearly. It also suits projects where buildability matters, because the builder shapes the design from the start.

Monument's design and construct work includes the Bransgrove Road Council Depot sign-writers building, the Fairvale Public School staffroom and uniform shop, and a canteen refurbishment at Cabramatta Public School that made the most of the working area for canteen staff. Several of its sports and amenities projects have been delivered the same way.

Where construct only fits

Construct only suits projects where the client needs close control of the design. Heritage buildings, projects with detailed agency standards and buildings that form part of a larger master design tend to sit here.

It also suits a client that has already paid for a full design and wants contractors to price against the same documents.

A middle path

Some clients want the builder's input without handing over the design. Early contractor involvement brings the contractor in while the design is still being developed, to advise on staging, programme and cost. The detail is in early contractor involvement and cost planning.

Questions to settle before choosing

• How complete is the design today?
• How much control does the client need over the final design?
• Is the site occupied, with staging the design has to allow for?
• Who should hold the risk if a design detail does not work?

Monument's own design and construct capability is covered in does Monument do design and construct.

Our capability