Guardian near completion on £60M project in London

Guardian Preservation Services are proud to be on time and nearing completion on a major Structural Waterproofing project in London. The project is the redevelopment of the Marylebone Police Station in the middle of London. The £60M project has seen Guardian commissioned by Galliford Try to provide structural waterproofing to the double basement area of this 90,000 sq ft construction. You can read more here in our latest Case Study.

1-9 Seymour Street London

In 2015, Westminster City Council’s planning department granted The Portman Estate planning permission to demolish the existing building at 1-9 Seymour Street, which had been Marylebone Police Station.

The scheduled demolition and clearing of the site was to make way for a new seven storey mixed use building, which was to include a two level basement, residential block, restaurant, retail space, commercial office block and school.

£60m Project

1-9 Seymour Street is a 90,000 sq ft technically challenging project with a multiple façade. Whilst the multiple façade is a key feature, it is also a disadvantage. A detailed design and a sound approach would be applicable to this project from the onset. The main contractor Galliford Try undertook the complex underpinning and formed the two levels of basement.

There is always a level of risk to damaging other buildings in the vicinity when dealing with demolition, re-build and basement construction, this risk was designed out in collaboration with renowned Architects Eric Parry. During this phase Galliford Try successful reached all of their goals without causing any damage to surrounding structures.


Ensuring a fully functional waterproofed basement which would accommodate the building and its future use.

Responsibility for full façade package including onerous performance criteria.

Multiple façade treatments with complex interfacing. Totally bespoke projecting glass and steel bays.

Bespoke vitreous enamel window liners.

Complex inner city environment with significant delivery challenges.

Guardian’s Award Winning Approach

This project required a sympathetic knowledgeable basement specialist. Guardian Preservation with its reputation of working with homeowners, surveyors, contractors, architects, landlords and management companies was a natural choice. Tim Herbert, CSSW qualified Structural Surveyor and partner at Guardian Preservation commenced his involvement in the project by giving careful consideration to products available, how they would be best suited to the project, that all BS8102:2009 standards and considerations were met, that the site was kept in a safe manner (health and safety) and that all Building Regulations were adhered to.

Waterproofing a basement ensures that the integrity of the structure is preserved whilst ensuring the usefulness of the basement. All basements should be constructed to cope with groundwater levels up to the full retained height of the basement. BS8102: 2009 sets out the scope and limitations for below ground structures, areas covered include:

waterproofing barrier materials,

waterproofing to construction joints within the RC frame construction

ensuring buildings are structurally integral with watertight construction

drained cavity construction and ground water assessment

ground water drainage and associated risk assessments

The Results

The basement structure has been constructed to cope with any future water ingress and will withstand the test of time. Galliford Try were thrilled with the outcome. The project was achieved on time and within budget. The finished project will be a truly stunning building that adds to the growing portfolio for all involved and will add to London’s ever evolving skyline and landscape.


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