What Does a Waterproofing Consultant Do at Each RIBA Stage?

Direct answer

A waterproofing consultant contributes at every RIBA stage from Stage 2 (Concept Design) through to Stage 6 (Handover), with the most critical interventions occurring at Stages 2 and 3 when the design philosophy is established, and the performance specification is written. Appointment at Stage 2 allows the waterproofing strategy to influence the cost plan, structural design and procurement approach before these are locked in. Conversely, appointment after Stage 3 significantly reduces the waterproofing consultant’s ability to add value, and increases the risk of waterproofing defects.

Full explanation

The RIBA Plan of Work provides the standard framework for organising a construction project into stages. Understanding what a waterproofing consultant does at each stage – and why the timing of their appointment matters – is essential for project managers, architects, and clients who are commissioning commercial developments with below-ground elements.

RIBA Stage 1: Preparation and Briefing

At Stage 1, the waterproofing consultant is not typically appointed but may provide preliminary advice if the project involves significant below-ground construction. This might include high-level risk commentary to inform the project brief, or advice on whether the proposed basement extent is feasible given known ground conditions. The key action at Stage 1 is ensuring that the brief recognises the need for specialist waterproofing input and that the appointment is programmed for early Stage 2.

RIBA Stage 2: Concept Design

This is the critical appointment point for a waterproofing consultant. At Stage 2, the consultant conducts the initial risk assessment, develops the waterproofing design philosophy and advises on the strategic approach to waterproofing the below-ground structure. The design philosophy establishes the grade of protection required for each zone, the primary waterproofing strategy (barrier, structurally integral, drained, or combination), and the key design assumptions.

Stage 2 is critical because the cost plan is being established. If the waterproofing consultant is not involved at this point, the cost plan will either omit adequate provision for waterproofing, or include a placeholder figure that bears no relation to the actual requirement. Once the cost plan hardens during Stage 3, introducing proper waterproofing provision becomes a cost increase rather than a planned element – often generating fee resistance and value engineering pressure that compromises the waterproofing solution.

The consultant also advises the structural engineer on waterproofing-related requirements for the concrete substructure, including crack width limitations, construction joint strategy and any requirements for integral crystalline or other concrete treatment systems. These decisions must be coordinated at Stage 2 because they affect reinforcement design and concrete specification.

RIBA Stage 3: Spatial Co-ordination

At Stage 3, the waterproofing consultant develops the design philosophy into a co-ordinated waterproofing strategy, resolving interfaces with the structural frame, drainage system, mechanical service penetrations and adjacent building elements. The performance specification is drafted during Stage 3, defining the requirements that specialist contractors will need to satisfy.

Stage 3 is also when the consultant co-ordinates with the structural engineer on construction joint locations, movement joint strategy and any temporary works requirements that affect the permanent waterproofing. These co-ordination issues are technically complex and require specialist input – they cannot be resolved by the structural engineer alone.

RIBA Stage 4: Technical Design

At Stage 4, the performance specification is finalised and issued for tendering. The consultant evaluates specialist contractor submissions, assesses the adequacy of proposed systems against the specification and provides a technical recommendation to the client. If a PCSA has been used, the consultant reviews the contractor’s detailed design proposals and confirms they satisfy the performance requirements and design intent.

The consultant also reviews the main contractor’s construction methodology for below-ground works, checking that the proposed sequence, temporary works, and site logistics are compatible with the waterproofing strategy.

RIBA Stage 5: Manufacturing and Construction

During construction, the waterproofing consultant provides construction monitoring – independent site inspections at critical hold points to verify that the waterproofing is being installed in accordance with the design intent and performance specification. This includes inspection of substrate preparation, membrane application, joint treatment, penetration sealing, and protection before backfill or follow-on trades.

The consultant also manages technical queries from the contractor, reviews proposed variations and advises on responses to unforeseen site conditions that affect the waterproofing. Construction monitoring is specialist technical assurance by the designer, confirming that the design intent is being achieved.

RIBA Stage 6: Handover

At handover, the consultant reviews the contractor’s as-built documentation, confirms that all specified testing and commissioning has been completed, and produces a handover report summarising the waterproofing design, key decisions made during construction, and maintenance requirements. The consultant may also advise on the scope and terms of waterproofing warranties and their relationship to the building’s maintenance strategy.