Glossary · Technical Design
RIBA Stage 4
RIBA Stage 4 — Technical Design — is the stage at which design is fully resolved, tender documents are prepared, and cost certainty is established before procurement begins.
What happens commercially at Stage 4
By the start of Stage 4, the cost plan should be at "stage 3" depth — every element priced against the design. During Stage 4, the cost plan is converted into tender documents: a Bill of Quantities or detailed schedule of works that contractors will price.
For the consultancy, Stage 4 is the most cost-intensive stage of work. Detailed estimates are produced. Sub-contractor procurement strategies are agreed. Long-lead items may already have been ordered. By the end of Stage 4, the client should know the project's final cost to within a small contingency.
Why it's the highest-stakes stage
Cost decisions made at Stage 4 are expensive to unwind. A specification change at Stage 4 might cost £5k in design rework; the same change at Stage 5 might cost £50k in variations and programme impact. Most consultancies hold a formal "Stage 4 sign-off" with the client before tender to lock down scope.
Common pitfalls
- Stage 4 cost not reconciled with Stage 3 cost plan. If the Stage 4 detailed estimate suddenly comes in 15% higher than the Stage 3 elemental plan, the client conversation is unpleasant. Reconcile before tender.
- Tender date set before design is ready. Pressure to procure can push tender out before Stage 4 is properly complete. The downstream cost is variations during construction.
- Cost not stress-tested for late-stage changes. Stage 4 cost should include sensitivity analysis — what if MEP comes in 10% higher? what if structural costs spike? The consultancy that doesn't do this gets a late surprise.
Related
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