Construction contracts define the legal and commercial relationship between the client and the contractor. Understanding the main contract types, what they mean for risk allocation, and how drawings and specifications fit into the contract is essential for anyone producing or reviewing construction documents.
The Main Contract Types
A lump sum contract (also called a fixed price contract) sets a single price for the complete scope of works. The contractor takes the risk of quantities — if it costs more to build than estimated, the contractor absorbs the difference. Lump sum contracts require a complete, coordinated drawing and specification set at tender stage; gaps in the documents become disputes. This is the most common contract type for straightforward buildings with well-defined scope.
A remeasurement contract (bill of quantities contract) pays the contractor at agreed rates for the quantities of work actually executed, measured on completion. The client takes the quantity risk — if more material is needed than estimated, the client pays. This suits projects where final quantities cannot be precisely determined at tender, such as civil engineering works with ground uncertainty.
A cost-plus contract reimburses the contractor’s actual costs plus an agreed fee or percentage. It offers maximum flexibility but minimum cost certainty — the client bears all cost risk. Used for emergency works, highly complex projects, or where the scope cannot be defined in advance.
Design-and-build contracts make the contractor responsible for both design and construction. The client issues an Employer’s Requirements document (the functional and performance brief); the contractor produces the Contractor’s Proposals (the design response) and then builds it. Design-and-build transfers design risk to the contractor and typically delivers faster programmes, but gives the client less control over detailed design decisions.
Standard Forms of Contract
Standard forms codify the rights and obligations of each party in a balanced, tested document. In the UK and internationally, the JCT (Joint Contracts Tribunal) suite covers building works at all scales. The NEC (New Engineering Contract) is widely used for civil engineering and infrastructure, emphasising collaborative management and early warning of problems. FIDIC (Fédération Internationale des Ingénieurs-Conseils) contracts are the global standard for international infrastructure projects — the Red Book for construction, the Yellow Book for design-and-build, the Silver Book for EPC/turnkey. In India, CPWD and MES standard conditions of contract apply to government works.
How Drawings Fit into the Contract
Contract drawings are the drawings listed in the contract as forming part of the agreement — they define the scope of work the contractor has priced. Any drawing issued after contract award that changes the scope is a variation, which entitles the contractor to additional payment and potentially additional time. This is why the drawing set at tender must be as complete as possible — every gap will become either a dispute or a cost.
The hierarchy of contract documents matters when there are conflicts between them. Typically: contract conditions override everything, then employer’s requirements or specification, then drawings, then bills of quantities. Understanding the hierarchy tells you which document governs when the drawing and the specification say different things about the same item.
Variations and Change Management
A variation (or change order) is any instruction that changes the scope, quality, or sequence of the work from what was contracted. Every variation must be formally instructed in writing — verbal instructions are not contractually binding under most standard forms. The cost of a variation is assessed against the rates in the contract bills or, if no applicable rate exists, by fair valuation. Time extensions are assessed separately from cost — a variation that causes delay to the critical path entitles the contractor to an extension of time as well as additional payment.
Practical Implications for Drawing Production
For anyone producing drawings, understanding contract implications means: never issue a drawing as a revision when the change is a scope addition (issue a variation instruction instead), maintain a clear drawing register showing which drawings were included in the tender set and which were issued post-contract, and flag design changes to the project manager before issuing revised drawings so the contractual impact can be assessed.
Conclusion
Construction contracts translate design intent into legal obligations. The drawings are not just technical documents — they are the primary definition of what the contractor has been paid to build. Clarity, completeness, and consistency in the drawing set are not just professional standards; they are contractual requirements that directly affect the cost, programme, and quality of what gets built.