Proteus Waterproofing delivers seamless sustainability at Marylebone House

Working alongside Blenheim House Construction and specialist contractor Essential Building Services Ltd, Proteus played a vital design-and-delivery role from the beginning - developing bespoke build-ups for multiple roof levels, integrating stormwater management, and solving complex thermal and aesthetic challenges across the main building and its new mews extension. The result is a refurbishment that exceeds modern performance targets while retaining the architectural heritage of this famous Marylebone landmark.

The multi-million development, led by client Beltane Asset Management, incorporated extensive new terraces, three additional storeys and a brand-new mews building replacing a defunct 1960s car park. In addition, Fletcher Priest Architects demanded good aesthetics, performance, and sustainability. This required comprehensive roofing and waterproofing systems that could adapt to diverse structural configurations, meet exacting thermal targets and incorporate both blue and green roof technologies. The result is a visually striking building with enhanced biodiversity and energy efficiency, offering richly landscaped rooftop environments and panoramic views of the City’s skyline.

Technical excellence

The Proteus in-house design team had to tackle some of the most complex challenges the company has ever faced. The new terraces and roofs involved a variety of substrates, threshold heights, load restrictions and stormwater attenuation requirements. Proteus provided bespoke U-value calculations for each roof zone, balancing thermal targets of 0.17 W/m²K with extremely tight build-ups.

In collaboration with the architect and façade specialists, Proteus devised customised thermal break courses of varying thicknesses for each terrace. Flashings had to be hidden and waterproofing integrated seamlessly with fenestration systems - an engineering feat that required new terminations to be designed directly into the window and door frames, all while conforming to BS6229:2018.

The complexity was magnified by the inclusion of both Blue Roof (attenuation) and Green Roof (biodiversity and aesthetic) systems across multiple levels. The Proteus Cold Melt® system enabled the delivery of a hybrid design by providing robust waterproofing over difficult build-ups. 

The works spanned across Levels 6 to 9 of the main building and the new Mews extension. Each terrace posed different design constraints and finishes - from porcelain tiles and planters to concrete slabs supporting M&E plant. The work began with Proteus Fastfill to level out the deck, followed by priming, vapour control layers, insulation using Pro-Therm HP PIR Plus and VIP, then waterproofing with Cold Melt® or Pro-BW® Plus, depending on area function.

Level 9 proved most complex, combining plant zones, terraces and extensive green roofs. Proteus’ Attenu8® full roof system and Easy Green Modular Tray systems created vibrant, sustainable rooftop environments while meeting attenuation and structural load requirements.

The Mews building required a different approach, using exposed cross-laminated timber (CLT) and glulam framing. The green roofs were secured to pitched areas using bespoke waterproofing straps and drainage trims. Proteus provided bespoke solutions for each section, overcoming design complexities and severe winter conditions.
During the colder months, newly poured concrete would typically delay waterproofing for up to 28 days. However, Proteus’ Cold Melt® allowed work to proceed just 72 hours after the concrete pour. This innovation kept the programme on track, which prevented costly delays and ensured full BBA-certified protection for the concrete.

Project management

Restrictive urban access, heavy congestion, and limited delivery slots were everyday challenges on site. Proteus worked closely with Essential Building Services and the Blenheim House team to coordinate just-in-time deliveries and stage material ordering by roof section to minimise site storage and disruption.

In line with their supply chain sustainability goals, Proteus even coordinated the delivery of Pro-Therm PIR insulation from Europe along with materials for another UK project - cutting emissions by 50% through consolidated transport.

Furthermore, Proteus’ detailed forecasting ensured availability of essential materials during high-demand periods, avoiding delays that could affect the overall schedule or budget. Each build-up was approved ahead of time with clear technical submittals and installation protocols, ensuring swift sign-off and seamless integration with surrounding trades.

Prioritising health and safety and the environment

Environmental performance was central to every aspect of this project. The main building achieved a 51.8% CO₂ reduction and 40% water consumption cut. With green roofs promoting biodiversity and air purification, along with blue roofs managing stormwater runoff, the environmental legacy of Marylebone House is significant.

All waterproofing systems supplied by Proteus were BBA certified, non-toxic in installation and cold-applied - eliminating fire risks. The Proteus Cold Melt® system also contains a high proportion of recycled rubber crumb and supports vapour diffusion, improving long-term durability of substrates.

The transformation of Marylebone House and the adjacent Mews Building has set a new benchmark for urban refurbishment and sustainable design. Thanks to Proteus Waterproofing’s strategic input and precision execution, this ambitious project exceeded both client and environmental expectations.

From cold-applied waterproofing to biodiversity-driven green roofs, Proteus demonstrated their technical leadership and commitment to greener, safer, more resilient buildings. Their work at Marylebone House is a great example of how innovation in waterproofing can directly contribute to climate-positive construction.