Project case study
Holden House
A facade-retention refurbishment over a complex double-storey basement. CLW was appointed waterproofing design consultant from RIBA Stage 3, took the design through Stage 4, and was novated to the contractor for delivery.
The scheme
Holden House is Derwent London’s refurbishment of a prominent Oxford Street building, designed by DSDHA with Gardiner & Theobald as project manager and Kier appointed as main contractor in 2026. The scheme retains the facades and includes a complex double-storey basement, with the existing below-ground levels brought back into commercial use.
CLW was appointed waterproofing design consultant from RIBA Stage 3.
What CLW did
Designed from the structure that exists. Refurbishing an existing basement is a different discipline from designing a new one. The existing structure, its current waterproofing condition and its historic service penetrations set constraints that a new-build specification cannot anticipate. The risk assessment under BS 8102:2022 was grounded in what the structure actually is rather than what a clean-sheet design would prefer it to be, and the system selection followed from that: the right answer on a retained basement is the system the structure can support, not the one that looks best on paper.
Stage 3 to Stage 4. CLW developed the waterproofing design through Stage 3 and completed the Stage 4 design for tender, coordinated with the facade retention and the structural works around the double basement.
Novated to the contractor. On appointment of the main contractor, CLW’s waterproofing consultant appointment was novated, so the designer who wrote the strategy carries it into construction rather than handing it over at tender. That continuity matters most on refurbishments, where the conditions uncovered on site routinely differ from the record drawings.
What this project illustrates
- Appointing the waterproofing designer at Stage 3 is late enough to need catching up, and early enough to still shape the answer. Stage 2 is better. See when to appoint a waterproofing consultant.
- Facade retention and basement reuse concentrate waterproofing risk at the junction between old and new. See waterproofing design for refurbishment and retrofit.
- Novation keeps the design intent intact through construction, provided the novated designer retains the authority to reject substitutions. See construction monitoring.
Project credit: Derwent London · DSDHA.
Working on a comparable scheme?
Independent waterproofing design from RIBA Stage 2 through construction monitoring. Defensible, document-led, contractor-agnostic.