Design development stage: concept to construction-ready documentation

TL;DR

Design development (DD) is the design stage that follows concept or sketch design and precedes full construction documentation. It resolves planning-compliant massing and layout into a coordinated set of drawings and specifications covering structure, services, external envelope, primary materials, and performance specifications. On Design and Construct (D&C) projects, the DD package is typically the technical brief issued at tender (roughly 60-80% complete depending on practice and project complexity): the consultant team has resolved the big calls, but detailed shop drawings, finishes schedules, and service-run drawings are still to follow. After novation, any gaps in the DD set become the builder’s scope risk, not a variation from the client. The commercial discipline for a builder: interrogate what is NOT resolved before pricing, and schedule every open item in the tender qualification.

The stage ladder

Design typically steps through three broad stages, though naming and percentage-complete conventions vary by practice, state, and contract form:

Concept or sketch design: massing, orientation, room adjacency, preliminary planning strategy. Drawings are exploratory; nothing is fixed. Used to obtain planning pre-lodgement meetings, brief sign-off, and early feasibility checking.
Design development: planning-compliant design resolved into coordinated documentation. Structure located and sized (preliminary), services strategy confirmed, external envelope materials selected, wet area and critical dimension layouts fixed. At the end of DD the project is buildable in principle; the documentation is not yet IFC but is detailed enough to price and to form a D&C technical brief (verified 2026-06-11 against standard Australian D&C procurement practice referenced in AIQS Project Management Guidelines and consistent with procurement descriptions across the Chalkline corpus including contracts/novation-design and trades/architect-building-designer).
Construction documentation (CD) (also called contract documents or issued-for-construction (IFC) documents): fully coordinated and detailed drawings, specifications, schedules, and consultant coordination drawings from which the builder constructs. The CD package is what a construct-only project puts to tender; under D&C, the builder typically produces CDs after novation.

What design development resolves

By the close of DD the consultant team should have locked:

Grid and levels: floor-to-floor heights, structural grid, datum levels, finished floor levels (FFLs) for wet areas and level entries.
External envelope: facade material, glazing extent and performance specification, roof form and material, insulation strategy (including NatHERS-pathway inputs for NatHERS assessors to model).
Wet areas and critical layouts: bathroom, laundry and kitchen layouts dimensioned to tolerances, hob heights, floor falls, waterproofing zones.
Structural system: primary structural framing type (concrete frame, steel, timber), preliminary beam and column sizes, slab type.
Services strategy: hydraulic, electrical, mechanical, and fire services system choices (not run-by-run; system-level decisions fixed, e.g. VRV vs split system, central hot water vs instantaneous).
Planning compliance: privacy and sight line screening and setback compliance resolved; shadow diagrams finalised for DA/CDC approval if not already issued.
Performance specifications: fire-rated systems nominated, acoustic separation approach confirmed, energy compliance pathway chosen (NatHERS or DTS).

Why builders care at DD

On a D&C project, the builder prices and subsequently accepts design liability from the DD set. Two commercial risks concentrate at this stage:

Pricing risk from gaps. Items resolved at DD are priceable; items left open (unspecified structure, provisional materials, undefined services routes) sit as contingencies or PC sums. The more open the DD package, the less reliable the lump-sum tender price.

Post-novation scope risk. Under a novation deed, the design freeze occurs at novation. Anything the client “was thinking about” at DD but did not confirm in writing becomes a builder-initiated variation after novation, which the builder now has to fund or fight for. A builder who does not interrogate the DD set before signing is pricing an open scope with no upside.

Milestone checklist: end of DD (builder review)

Before pricing or accepting a D&C package at DD stage, check:

Structural grid and floor-to-floor heights fixed on the architectural drawings
External envelope materials and glazing performance specs confirmed (not TBC or NTS)
Wet area layouts dimensioned; FFL and drainage points confirmed
NatHERS certificate issued (or modelling underway with confirmed specification inputs)
Structural engineer’s preliminary sizing report issued (spans, beam depths, slab type)
Services system choices confirmed in a consultant’s report or services design statement
Planning approval drawings issued or DA-approved drawings match the DD set
Schedule of unresolved items issued by the design team (what is intentionally left to CD stage)

The last item is the most useful: a design team that proactively issues a schedule of open items is honest about what the builder is pricing. A design team that has no such schedule has either resolved everything (rare) or hasn’t thought it through.

Builder-facing read

Ask the design team for a schedule of unresolved items at tender. Put every open item in your tender qualification, with your pricing assumption. Unresolved material selections become PC sums with a real-cost cap; unresolved structural elements get a contingency line that you control. Do not absorb ambiguity in the hope it resolves cheaply: it rarely does.

References

AIQS (Australian Institute of Quantity Surveyors), Project Stages and Documentation guidance (general reference; design stage ladder aligned to standard industry practice) (verified 2026-06-11, aiqs.com.au).
ABCB (Australian Building Codes Board), NatHERS Accredited Software pathway under NCC 2022 Volume Two Specification 42 (relevant to design-stage energy compliance locking; NatHERS assessment is a design development milestone, not a construction milestone) (verified 2026-06-11, abcb.gov.au).
Consistent with stage conventions described in: Novation of design consultants (Chalkline, 2026-05-15) and Architect vs building designer (Chalkline, 2026-05-10), both referencing “design development stage” as the pre-tender documentation milestone.