CSMANLTD provides specialist basement construction services in Greenwich for homeowners, property developers and commercial clients looking to create additional space below existing buildings or within suitable external areas. Basement construction requires considerably more than excavation. The project must account for the existing building structure, foundations, ground conditions, groundwater, drainage, flood risk, neighbouring properties and the proposed use of the basement.
Our team combines practical construction experience with expertise in groundworks, underpinning, piling, deep foundations, reinforced concrete, structural works, waterproofing and drainage. This allows us to develop basement construction solutions around the actual requirements of each Greenwich property.
Whether you are considering an under-house basement, garden basement, basement extension or conversion of an existing cellar, CSMANLTD can help develop a practical construction strategy from the initial assessment through to completion.
Basement construction in Greenwich can involve a number of structural and planning considerations. Properties vary considerably, from traditional houses and period buildings to modern residential developments and larger commercial sites.
Before excavation starts, it is important to understand the relationship between the proposed basement and the existing foundations. Groundwater, drainage, flood risk and neighbouring structures must also be considered as part of the project.
CSMANLTD takes an engineering-led approach to basement construction. Our team can coordinate excavation, temporary works, underpinning, structural construction, waterproofing and drainage to create a safe and durable underground structure.
CSMANLTD has more than 10 years of practical experience in groundworks, deep foundations, piling, underpinning and basement construction throughout London.
Our basement construction services can be adapted to suit residential, commercial and development projects.
New Basement Construction
We construct new basements beneath existing properties and within suitable external areas. The work may include excavation, temporary support, reinforced concrete construction, structural works, waterproofing and drainage.
The construction method is selected according to the site’s access, ground conditions, existing foundations, excavation depth and surrounding structures.
Under House Basement Construction
Creating a basement beneath an existing property requires careful management of the building’s existing foundations.
Where excavation extends below the existing foundation level, underpinning or another engineered foundation solution may be required. The work must be carefully sequenced to maintain structural stability during excavation and construction.
CSMANLTD can coordinate underpinning, excavation and structural works as part of the overall basement construction process.
Garden Basement Construction
Where the property layout allows, a basement can be constructed beneath a garden or external area.
Garden basement construction may allow different excavation techniques compared with an under-house basement, depending on site access and the relationship between the proposed basement and existing structures.
The feasibility of the project depends on planning requirements, ground conditions, drainage, flood risk, access and the surrounding properties.
Basement Excavation
Basement excavation involves removing substantial quantities of soil to create the required underground space. The excavation method must be carefully selected based on ground conditions, depth, access and structural requirements.
Our team can undertake controlled excavation as part of a wider basement construction package, including temporary works, underpinning and structural support where required.
Basement Extension and Conversion
If you already have a basement or cellar, we can help extend, strengthen or convert the space.
Depending on the existing structure, works may include lowering the basement floor, extending the footprint, improving waterproofing, installing drainage or strengthening foundations.
Each property is assessed individually before determining the most suitable construction method.
Underpinning for Basement Construction in Greenwich
Underpinning is often an important consideration when excavation takes place below an existing building or close to its foundations.
The correct underpinning method depends on the existing foundation design, soil conditions, excavation depth, structural loads and proposed basement layout.
CSMANLTD provides underpinning and foundation solutions as part of its wider basement construction services. Our team considers the sequencing of temporary and permanent works to help maintain structural stability throughout the project.
Basement Structural Engineering and Groundworks
A successful basement project requires close coordination between structural engineering and construction.
Our capabilities include:
CSMANLTD also provides design and engineering support, helping clients assess different construction methods and develop practical solutions based on actual site conditions.
Basement Waterproofing and Drainage in Greenwich
Waterproofing and drainage are critical elements of basement construction.
Because basements are located below ground level, the structure needs to be designed to manage water effectively. The waterproofing approach depends on factors including ground conditions, groundwater, basement use and the structural design.
Drainage should also be considered during the early stages of the project. Retrofitting drainage after the basement has been excavated and constructed can create additional cost and disruption.
CSMANLTD can coordinate waterproofing and drainage as part of the wider basement construction strategy, including sump pumps and other drainage solutions where required.
Planning Considerations for Basement Construction in Greenwich
Greenwich has specific planning guidance relating to basement development.
Royal Greenwich states that basement development includes excavation to create new or additional usable floorspace below ground level, including extensions to existing basement accommodation and the conversion of cellars into habitable accommodation. The council states that most basement proposals require planning permission, although certain circumstances may fall under permitted development.
The council’s guidance also states that planning applications for basement development must be accompanied by a Basement Impact Assessment. Depending on the site, this can consider groundwater, aquifers, watercourses, geology, flooding, drainage, structural stability, construction methods, neighbouring properties, public sewers and transport infrastructure.
This makes early technical assessment particularly important when planning a basement in Greenwich.
Basement Impact Assessment in Greenwich
A Basement Impact Assessment, commonly referred to as a BIA, is an important part of the planning process for basement development in Greenwich.
The council identifies several areas that may need to be assessed, including:
The exact information required depends on the individual site and proposal. Royal Greenwich also states that structural stability should be addressed through a Structural Method Statement signed and endorsed by a suitably qualified Chartered Civil or Structural Engineer.
For this reason, basement construction should be considered alongside engineering and planning requirements rather than treating excavation as a separate construction activity.
Flood Risk and Basement Development in Greenwich
Flood risk is particularly important when considering basement development.
Royal Greenwich’s guidance states that basement development will not be permitted in Flood Zone 3 and will not normally be permitted in Flood Zone 2 unless specific conditions are met, such as avoiding habitable rooms or demonstrating that flood risk has been appropriately minimised. The guidance also highlights the use of sustainable drainage measures where appropriate.
The flood risk classification of the property should therefore be established during the early stages of a proposed basement project.
This is one reason why a site-specific feasibility assessment is important before committing to excavation or construction.
Single Storey Basement Construction in Greenwich
Greenwich’s current urban design guidance states that only single-storey basement extensions will be supported due to concerns about environmental impact and increased flood risk associated with multiple-storey excavations. The guidance also states that basement extensions should generally remain within the footprint of the host building so that the development remains subordinate in scale.
This means that the size, depth and layout of a proposed basement should be considered carefully during the design stage.
A technically feasible excavation is not necessarily a planning-approved proposal, so early coordination between the design, engineering and construction teams is important.
Basement Construction for Greenwich Properties
Greenwich contains a wide range of residential and commercial properties, creating different construction challenges from one site to another.
A basement project may involve excavation below an existing property, construction close to neighbouring buildings, restricted site access or work around existing underground infrastructure.
Our team considers key factors such as:
The construction methodology is then developed around the individual site.
Choosing an experienced basement contractor is important because underground construction combines excavation, structural engineering, foundations, waterproofing and drainage.
More than 10 years of experience
CSMANLTD has practical experience across groundworks, deep foundations, piling, underpinning and basement construction throughout London.
Engineering-led construction
We consider structural stability, excavation requirements and construction sequencing before work begins.
Integrated services
Our capabilities include excavation, underpinning, piling, foundations, structural works, waterproofing and drainage.
Residential and commercial experience
We work with homeowners, developers and commercial clients on projects ranging from residential basements to larger construction developments.
Practical construction methods
Different sites require different solutions. We assess the project and consider appropriate excavation and foundation methods rather than applying a standard approach to every property.
Design and build capability
Our design and engineering team can work alongside the construction team to develop practical and cost-conscious solutions.
Our Basement Construction Process in Greenwich
Site Assessment
We begin by understanding the property, existing foundations, site access, proposed basement and surrounding conditions.
Feasibility and Engineering
The proposed excavation and structural requirements are reviewed to establish whether the project is technically suitable.
Planning and Technical Preparation
Planning requirements, Basement Impact Assessment requirements, structural information and other technical matters are considered before construction begins.
Excavation and Temporary Works
The ground is excavated using a controlled construction methodology appropriate to the site.
Underpinning and Foundation Works
Where required, underpinning, piling or other foundation solutions are completed to support the existing structure and proposed basement.
Basement Structure
The basement is constructed using the specified structural system, which may include reinforced concrete walls, slabs and other structural elements.
Waterproofing and Drainage
Waterproofing and drainage systems are installed as part of the overall below-ground construction strategy.
Completion
The completed basement is prepared for its intended use, whether that is additional living accommodation, a home office, gym, entertainment area, storage or another suitable purpose.
Basement Construction for Homeowners and Developers
A basement can provide additional usable floor space where conventional extensions may be restricted by the property’s layout or available land.
For homeowners, a well-designed basement can create space for a home office, gym, guest accommodation, entertainment area or other practical uses.
For developers, basement construction can form part of a wider residential or commercial development. CSMANLTD can support projects involving excavation, piling, underpinning, foundations, structural concrete and associated groundworks.
The company’s wider construction services are designed to coordinate below-ground works with the structural requirements of the overall development.
Start Your Basement Project in Greenwich
If you are considering basement construction in Greenwich, an early feasibility assessment can help establish the technical, structural and planning considerations associated with the proposal.
CSMANLTD can assist with basement excavation, underpinning, piling, foundations, structural construction, waterproofing, drainage and associated groundworks.
Contact CSMANLTD to discuss your Greenwich basement construction project and request a consultation.
Most basement proposals in Greenwich require planning permission, although certain circumstances may qualify as permitted development. Royal Greenwich’s guidance specifically states that most basement proposals require planning permission.
A Basement Impact Assessment evaluates the potential effects of basement development. Depending on the site, it can address groundwater, flooding, drainage, geology, structural stability, construction methods, neighbouring properties, public sewers and other relevant factors.
Royal Greenwich’s current guidance states that only single-storey basement extensions will be supported because of the environmental impact and increased flood risk associated with multiple-storey excavations.
Yes, an under-house basement can be possible where the property and planning requirements allow it. The project may require underpinning or another engineered foundation solution depending on the existing structure.
Garden basement construction may be possible where the site is suitable and the proposal meets planning and technical requirements. Site access, flood risk, drainage, ground conditions and the relationship with neighbouring properties all need to be assessed.
Not every basement requires the same foundation solution. Underpinning may be necessary where excavation affects the existing foundations. The appropriate method should be established through structural assessment and engineering design.
Yes. Greenwich’s planning guidance specifically addresses flood risk and states that basements will not be permitted in Flood Zone 3 and will not normally be permitted in Flood Zone 2 unless specified conditions are satisfied.
The waterproofing approach depends on the basement structure, ground conditions, groundwater and intended use. CSMANLTD can incorporate waterproof concrete, membranes, drainage systems and sump pump arrangements where appropriate.
There is no fixed price because every basement project is different. Costs can depend on basement size, excavation depth, soil conditions, access, foundations, underpinning, structural requirements, waterproofing, drainage and the construction methodology.
The programme depends on the size and complexity of the project, excavation requirements, structural works, access and planning process. A project-specific programme can be developed following an initial assessment.
Yes. Older properties require careful assessment of existing foundations, structural condition and neighbouring structures before excavation. The construction method can then be developed around the property’s specific requirements.
Yes. CSMANLTD can coordinate excavation and underpinning as part of an integrated basement construction package where the project requires both services.
Yes. Drainage is an important part of basement construction, particularly where the site has groundwater or flood-related considerations. Our services can include basement drainage and pumping arrangements where required.
Yes. CSMANLTD works with developers and commercial clients as well as residential property owners. Our capabilities include excavation, piling, underpinning, foundations and structural construction for larger developments.
CSMANLTD combines practical construction experience with groundworks and engineering capabilities. Our services cover excavation, underpinning, piling, foundations, structural works, waterproofing and drainage, allowing the different elements of a basement project to be coordinated through one experienced construction team.
TESTIMONIALS
We hired CSMANLTD to design and build a basement under our family home, and the entire process was seamless. Their team took care of everything—from underpinning and excavation to drainage and structural integrity—offering expert advice at every stage. The project was completed on time and within budget. We now have a stunning living space that has transformed our home. Highly recommend their design and build service!
construction worker
CSMANLTD has become our go-to partner for pre-construction groundwork and basement development. Their in-house engineering team provides invaluable insight during the early stages, allowing us to begin on-site work while final designs are being approved. Their ability to handle piling, deep excavations, and below-ground utilities has saved us significant time and cost across multiple projects. A truly unique and reliable approach to construction.
construction worker
We collaborated with CSMANLTD on a mixed-use development requiring complex temporary works and deep foundation solutions. Their expertise in structural engineering and piling was evident from day one. They delivered a robust, cost-effective design-build solution that kept the project on track. Safety was a top priority on site, and their team operated with professionalism throughout. A standout contractor in the industry.
construction worker
As architects, we value contractors who understand both design intent and structural feasibility. CSMANLTD bridges that gap perfectly. Their in-house engineers work closely with our team to optimise structural frames, foundations, and basement construction—often suggesting innovative, cost-saving alternatives without compromising safety. They are a true extension of our professional team.
construction worker
Our Victorian house had foundation issues and limited space. CSMANLTD assessed the structure, recommended underpinning, and constructed a full basement beneath our garden—maximising space without affecting the main house. The work was clean, safe, and incredibly well-managed. Now we have a gym, cinema room, and extra bedroom. We couldn’t be happier with the result.
construction worker
