Creating additional space below an existing property requires careful planning, structural engineering and controlled excavation. CSMANLTD provides specialist basement construction in Kensington for homeowners, developers and commercial property owners looking to create new space below their buildings or gardens.
Our team has more than 10 years of practical experience in groundworks, deep foundations, piling, underpinning, excavation and basement construction. We combine engineering knowledge with practical construction experience to develop basement solutions suited to the individual property and site conditions.
Kensington contains a wide range of properties, including traditional townhouses, period homes, terraces and larger residential developments. Basement work in this type of built environment requires particular attention to neighbouring structures, existing foundations, drainage, access, trees, heritage considerations and construction impact.
CSMANLTD provides basement construction services from the initial assessment through structural works and below ground construction. Depending on the property, a project can include excavation, underpinning, reinforced concrete construction, piling, waterproofing, drainage and temporary works.
Our in house design and engineering team can assess the proposed basement and help establish a practical construction approach before excavation begins.
We understand that every Kensington property has different structural and access conditions. The appropriate method may depend on the existing foundations, soil conditions, depth required, available access and relationship with neighbouring buildings.
New Basement Construction
We construct new basements beneath existing properties or within suitable garden areas. The construction approach is developed around the structural requirements of the building and the proposed use of the new space.
New basement construction can involve excavation, temporary works, foundation strengthening, reinforced concrete walls and slabs, waterproofing and drainage.
Under House Basement Construction
Creating a basement beneath an existing house requires careful sequencing because the original foundations may need to be extended or strengthened.
CSMANLTD can undertake underpinning and associated structural works to create additional depth below an existing building. Excavation can then be carried out in controlled stages based on the approved structural methodology.
Garden Basement Construction
A garden basement can provide additional space while retaining the main footprint of the property above ground. The feasibility of this type of project depends on the available garden area, existing structures, trees, drainage and planning requirements.
Our team can assess the proposed excavation and advise on suitable construction methods.
Basement Excavation
Excavation is one of the most important stages of basement construction. The excavation method needs to consider ground conditions, neighbouring properties, existing foundations and site access.
Where appropriate, excavation can be completed in controlled stages to reduce structural risk and maintain stability during construction.
Basement Extension and Conversion
If a property already has a basement or cellar, it may be possible to extend or improve the existing below ground space.
CSMANLTD provides basement excavation, structural strengthening, waterproofing and drainage solutions for suitable conversion and extension projects.
Underpinning for Kensington Basements
Underpinning may be required when a basement is being constructed beneath an existing building and the existing foundations need to be extended to a lower level.
The exact underpinning method depends on the building, ground conditions and structural design. CSMANLTD can coordinate underpinning with excavation and reinforced concrete construction so that the different stages of the basement project work together.
Structural Engineering and Groundworks
Basement construction is not simply an excavation project. The finished structure needs to transfer loads safely and manage ground and water conditions.
Our basement projects can incorporate structural concrete, reinforced concrete walls and slabs, piling, underpinning, temporary works and other foundation solutions where required.
Our design and build approach allows construction considerations to be assessed early rather than being left until excavation has already started.
Basement Waterproofing and Drainage in Kensington
Water management is an important part of any basement project.
CSMANLTD can provide waterproofing and drainage solutions designed around the proposed basement construction. Depending on the project, this can include waterproof concrete, membranes, drainage channels, sump pumps and associated systems.
Our previous basement work has included reinforced waterproof concrete construction, drainage and sump pumps, with internal walls finished using a Delta membrane system.
The waterproofing strategy should be established before construction so that drainage requirements are properly incorporated into the structural design.
Planning Considerations for Basement Construction in Kensington
Basement projects in Kensington and the Royal Borough of Kensington and Chelsea need to be assessed against the planning requirements applicable to the individual property.
RBKC basement policy includes controls relating to the size of basements, garden areas, basement depth, trees, heritage assets, lightwells, drainage, construction impacts and structural stability. The policy generally limits basement development to no more than 50% of each garden or open part of the site and generally to one basement storey.
Planning requirements can also depend on whether the property is listed, located within a conservation area or affected by other planning restrictions.
For this reason, basement feasibility should be considered before committing to excavation or construction.
Kensington Basement Size and Garden Requirements
The available garden or open area can be an important factor when considering a basement extension.
RBKC Policy CL7 states that basement development should generally not exceed 50% of each garden or open part of the site, while the unaffected garden should remain as a single area where applicable.
This means that the available site area should be assessed during the early design stage rather than assuming that the entire garden can be excavated.
Listed Buildings and Heritage Properties
Kensington contains many properties with architectural and historic significance. Basement proposals affecting listed buildings or their settings require particular care.
RBKC policy states that basement development should not harm the significance of heritage assets and places restrictions on excavation underneath listed buildings.
Where heritage considerations apply, the basement design and construction approach should be developed with the relevant planning and professional requirements in mind.
Lightwells and External Basement Features
Natural light and ventilation can be important when creating habitable basement accommodation. However, external features such as lightwells can change the appearance of a property.
RBKC policy places restrictions on introducing front or side lightwells and railings where these are not established and positive features of the local streetscape. External elements such as rooflights, plant and means of escape should also be designed sensitively.
Sustainable Drainage
Basement construction also needs to consider how rainwater and surface water are managed.
RBKC basement policy requires sustainable urban drainage measures and refers to maintaining permeable soil above basement areas beneath gardens.
A suitable drainage strategy can therefore form an important part of the basement design rather than being treated as an additional item after excavation.
Protecting Structural Stability
Kensington is a densely developed urban area where neighbouring properties may be close to the proposed excavation.
RBKC policy specifically requires basement development to safeguard the structural stability of the application building, nearby buildings and infrastructure, including London Underground tunnels and the highway.
CSMANLTD approaches basement construction with structural stability, temporary works and excavation sequencing considered as part of the overall project.
Basement Construction for Kensington Properties
Whether you own a townhouse near Kensington High Street, a property around South Kensington, a home close to Earl’s Court or another property within the Kensington area, the construction strategy needs to reflect the individual site.
Factors that may influence the project include:
Existing foundations
Ground conditions
Basement depth
Property footprint
Garden size
Neighbouring structures
Access for excavation and materials
Drainage requirements
Trees and landscaping
Planning and heritage considerations
The right construction method can only be determined after the property and proposed basement have been properly assessed.
CSMANLTD is a specialist groundworks and basement contractor with more than 10 years of practical construction experience.
Our capabilities include:
Basement construction
Underpinning
Deep foundations
Piling
Groundworks
Structural concrete
Temporary works
Waterproofing
Drainage
Basement excavation
Our in house design and engineering team works with the construction team to develop practical solutions based on the actual site conditions.
We also have experience with large scale basement construction, including a 500m² basement and underpinning project.
Site Assessment
We review the property, proposed basement area, access and existing structural conditions.
Design and Engineering
The basement structure, excavation approach, foundations, temporary works, waterproofing and drainage requirements are assessed.
Planning and Approvals
The project team can work with the required professional information and planning requirements applicable to the property.
Excavation and Temporary Works
Excavation is completed using a controlled construction sequence designed around the approved structural methodology.
Structural Construction
Underpinning, reinforced concrete walls, slabs, foundations and other structural works are completed as required.
Waterproofing and Drainage
Waterproofing and drainage systems are installed as part of the below ground construction.
Completion
Once the structural and below ground works are complete, the project can move forward to internal fit out and finishing.
Basement Contractors for Homeowners and Developers
Our basement construction services are suitable for homeowners seeking additional space as well as developers working on residential and commercial projects.
We can provide structural basement construction as part of a wider design and build arrangement, including excavation, foundations, drainage, concrete structures and associated below ground works.
A basement can be considered for many types of properties, including period homes and townhouses. Suitability depends on the existing structure, foundations, ground conditions, available space and the proposed design.
The property should be reviewed for its existing foundations, ground conditions, drainage, access, neighbouring structures, trees, garden area and applicable planning restrictions. These factors can influence both feasibility and construction method.
Any excavation close to adjoining properties needs to be carefully engineered. Foundation depth, ground movement, temporary support and the sequence of excavation should be considered before work begins.
A basement can potentially be designed for uses such as living areas, bedrooms, home offices, gyms or entertainment spaces, subject to the property’s design, building regulations, planning requirements and appropriate ventilation and natural light.
The required foundation arrangement depends on the existing building and proposed excavation depth. Solutions may include underpinning, reinforced concrete foundations or piling where appropriate.
Many basement projects require temporary works during excavation and structural construction. The type of support depends on the ground conditions, building structure, excavation depth and surrounding properties.
Soil removal is planned according to the site access, excavation method and available working space. Restricted access properties may require a carefully sequenced approach for removing excavated material.
Yes. Drainage can be designed into the basement from the construction stage. Depending on the project, this may include drainage channels, sump arrangements and pumping systems.
Groundwater conditions need to be assessed during the design stage. The basement construction and waterproofing strategy can then be developed to manage water appropriately for the site.
Potentially. Access is an important factor when planning excavation, material delivery and removal of spoil. The construction method can be adapted to the practical limitations of the site where feasible.
Yes. Existing trees and their root zones should be considered before finalising the basement footprint. Their location can influence excavation, structural design and the amount of garden that can be developed.
In suitable properties, an existing cellar may be improved through structural alterations, increased usable space, waterproofing, drainage, ventilation and other works. The existing condition needs to be assessed first.
A basement extension involves excavation below ground and can affect existing foundations, groundwater, drainage and neighbouring structures. It therefore requires a different structural and construction approach from a typical above ground extension.
Yes. CSMANLTD provides excavation together with groundworks, underpinning, piling, reinforced concrete, temporary works, waterproofing and drainage where required for the project.
Waterproofing should be considered during the design and structural planning stage. Integrating it into the basement construction programme helps ensure that drainage and water management are properly coordinated.
In some cases, yes. The proposed basement footprint can be developed with the existing garden, landscaping, trees and drainage requirements in mind, subject to the applicable planning restrictions.
Useful information includes the property location, existing floor plans, photographs, the approximate area you want to excavate, the intended use of the basement and details of any existing cellar or basement.
You can contact CSMANLTD with your property details and proposed basement requirements. The team can then discuss the likely structural, excavation, groundworks, waterproofing and drainage considerations for the project.
If you are planning to create additional space below your Kensington property, CSMANLTD can help with the structural and construction requirements.
From excavation and underpinning to reinforced concrete, waterproofing and drainage, our team can develop a practical basement construction approach based on your property and project requirements.
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
