FAQs – Basement Construction | Making Space Below Ground

Question 1

What is basement construction?

Accepted Answer

Basement construction involves excavating beneath an existing or new property to create additional living or commercial space.

Question 2

Can every house have a basement built underneath it?

Accepted Answer

Most properties are suitable, although this depends on factors such as ground conditions, existing foundations, drainage and access. We can assess your property during a site survey.

Question 3

How much does a basement construction project cost?

Accepted Answer

Every project is different. The cost depends on the size, depth, access, ground conditions and structural requirements. We provide free, no-obligation quotations.

Question 4

How long does a basement project take?

Accepted Answer

Most basement shell construction projects take between 10 and 20 weeks, depending on the complexity of the works.

Question 5

Does a basement add value to my property?

Accepted Answer

Yes. A professionally constructed basement can significantly increase both the usable living space and the overall value of your home.

Question 6

How much value does a basement add to a house in London?

Accepted Answer

In London, a well-constructed basement can add between 10% and 15% to the value of a property, and in some cases more, depending on the size of the space created and the location.

Question 7

Can I stay in my home while the basement is being built?

Accepted Answer

In many cases, yes. This depends on the type of works being carried out and access arrangements.

Question 8

Can you excavate beneath an existing property?

Accepted Answer

Yes. We specialise in basement excavation beneath existing homes using safe, engineered construction methods.

Question 9

Can you build a basement beneath an existing extension?

Accepted Answer

Yes. Subject to structural design and site conditions, we can excavate beneath existing extensions as well as the main property.

Question 10

Can you manage the entire basement shell construction?

Accepted Answer

Yes. We provide a complete basement shell package, including excavation, underpinning, reinforced concrete, waterproofing and drainage.

Question 11

Can you manage the entire project from start to finish?

Accepted Answer

Yes. We can manage every stage of your basement shell construction, from excavation and underpinning through to reinforced concrete and waterproofing.

Question 12

What can I use my basement for?

Accepted Answer

Basements are commonly used as home cinemas, gyms, bedrooms, offices, utility rooms, games rooms, wine cellars or additional family living space.

Question 13

Is it worth building a basement in London?

Accepted Answer

Yes. With London property prices at a premium, creating additional space below ground is often far more cost-effective than moving to a larger property or building an extension above ground.

Question 14

How deep can a basement be?

Accepted Answer

The depth of a basement depends on the structural design, ground conditions and the intended use of the space. Most residential basements are between 2.4m and 3m in finished ceiling height. We work to the depth specified by your structural engineer.

Question 15

What is a basement shell?

Accepted Answer

A basement shell is the structural construction of the basement space — including excavation, underpinning, reinforced concrete walls and slab, and waterproofing — ready for fit-out by others. We specialise in delivering the complete basement shell.

Question 16

Is basement construction disruptive?

Accepted Answer

Construction inevitably creates some disruption, but our experienced team works efficiently to minimise inconvenience and keep your project running smoothly.

Question 17

Is basement construction noisy?

Accepted Answer

There will inevitably be some noise during excavation and structural works, but we always aim to minimise disruption and keep neighbouring properties informed where appropriate.

Question 18

Do you work in London clay?

Accepted Answer

Yes. We have extensive experience working in London clay, which is the most common ground condition across much of Greater London. Our team is well-versed in the specific challenges and techniques required.

Question 19

Do I need planning permission for a basement?

Accepted Answer

Some basement projects require planning permission, while others fall under permitted development. We can advise you based on your property and local authority requirements.

Question 20

Is a basement permitted development?

Accepted Answer

In many cases, basement construction beneath a house falls under permitted development rights, meaning planning permission is not required. However, this depends on your local authority, whether the property is listed, and whether it is in a conservation area. We recommend checking with your local planning department or architect.

Question 21

Do I need Building Regulations approval for a basement?

Accepted Answer

Yes. All basement construction work requires Building Regulations approval. This covers structural integrity, waterproofing, ventilation, fire safety and means of escape. We carry out all works in accordance with current Building Regulations.

Question 22

Will my neighbours be affected?

Accepted Answer

We carefully plan every project to minimise disruption, following all relevant health and safety procedures and local authority requirements.

Question 23

Will I need a Party Wall Agreement?

Accepted Answer

If the work affects a shared wall or neighbouring property, a Party Wall Agreement may be required. We can explain the process and work alongside your appointed surveyor.

Question 24

What is a Party Wall Agreement and do I need one?

Accepted Answer

A Party Wall Agreement is a legal document that protects both you and your neighbours when construction work affects a shared wall or boundary. If your basement project involves excavation near a neighbouring property or affects a party wall, you will likely need one. A Party Wall Surveyor can advise you.

Question 25

Are your works Building Control approved?

Accepted Answer

Yes. All structural works are carried out in accordance with current Building Regulations and inspected where required.

Question 26

Do you work from structural engineer drawings?

Accepted Answer

Yes. All work is completed strictly in accordance with structural engineer designs and current Building Regulations.

Question 27

Do you work with architects and structural engineers?

Accepted Answer

Yes. We regularly work alongside architects, structural engineers and project managers to ensure every project runs smoothly.

Question 28

Do I need a structural engineer for a basement?

Accepted Answer

Yes. A structural engineer is essential for any basement project. They will design the underpinning scheme, reinforced concrete specification and waterproofing strategy to ensure the structure is safe and compliant with Building Regulations.

Question 29

Will my basement be waterproof?

Accepted Answer

Yes. Every basement we construct includes a waterproofing system designed in accordance with BS 8102 to protect against water ingress.

Question 30

What waterproofing system do you install?

Accepted Answer

We install industry-leading waterproofing systems, including Delta cavity drain membranes, drainage channels and sump pump systems where required.

Question 31

What is cavity drain waterproofing?

Accepted Answer

Cavity drain waterproofing (also known as Type C waterproofing) uses a studded membrane fixed to the walls and floor to manage any water that enters the structure, directing it to a drainage channel and sump pump. It is one of the most reliable and widely used systems for basement waterproofing in the UK.

Question 32

What is BS 8102?

Accepted Answer

BS 8102 is the British Standard that sets out the code of practice for the protection of below-ground structures against water ingress. All waterproofing systems we install are designed and specified in accordance with this standard.

Question 33

What is a sump pump and do I need one?

Accepted Answer

A sump pump is an electric pump installed in a pit (sump) at the lowest point of the basement drainage system. It automatically pumps away any water collected by the cavity drain membrane. Most waterproofed basements in the UK include a sump pump as part of the system.

Question 34

Can you convert an existing cellar?

Accepted Answer

Yes. Existing cellars can often be converted into dry, usable living spaces for a wide range of purposes.

Question 35

What is the difference between a cellar and a basement?

Accepted Answer

A cellar is typically an existing below-ground space, often with limited headroom, used for storage. A basement is a fully constructed, habitable below-ground space with adequate ceiling height, waterproofing and ventilation. We can construct new basements and convert existing cellars into usable living space.

Question 36

Do you carry out underpinning as part of the project?

Accepted Answer

Yes. We undertake all necessary underpinning works where required to safely support the existing structure.

Question 37

What is underpinning?

Accepted Answer

Underpinning is the process of strengthening and stabilising the foundations of an existing building. In basement construction, it is used to safely lower the floor level beneath an existing structure by excavating and constructing new mass concrete or reinforced concrete foundations in sections.

Question 38

What is mass concrete underpinning?

Accepted Answer

Mass concrete underpinning is the most common method used in residential basement construction. It involves excavating beneath the existing foundations in carefully sequenced sections and filling each section with concrete to create new, deeper foundations that support the structure above.

Question 39

Do you provide reinforced concrete works?

Accepted Answer

Yes. We carry out reinforced concrete walls, slabs, foundations and structural concrete works as part of the basement construction package.

Question 40

Do you provide structural concrete works?

Accepted Answer

Yes. Our experienced team specialises in reinforced concrete walls, slabs, beams and structural concrete construction as part of basement projects.

Question 41

What is a reinforced concrete slab?

Accepted Answer

A reinforced concrete slab is a structural floor or ceiling element made from concrete with steel reinforcement bars (rebar) cast within it. In basement construction, the ground-bearing slab forms the floor of the basement and is a critical structural element.

Question 42

Do you remove all excavated material?

Accepted Answer

Yes. We safely remove and dispose of all spoil generated during excavation unless otherwise agreed.

Question 43

How do you deal with excavated soil?

Accepted Answer

All excavated spoil is removed safely from site using licensed waste carriers unless otherwise agreed with the client.

Question 44

What groundworks are involved in a basement project?

Accepted Answer

Groundworks for a basement project typically include initial excavation, temporary works and shoring, drainage diversions, and preparation of the formation level ready for the structural concrete works. We carry out all groundworks as part of our basement construction service.

Question 45

What is underpinning?

Accepted Answer

Underpinning is the process of strengthening and stabilising the foundations of an existing building. In basement construction, it is used to safely lower the floor level beneath an existing structure by excavating and constructing new mass concrete or reinforced concrete foundations in carefully sequenced sections.

Question 46

Why is underpinning needed?

Accepted Answer

Underpinning is needed when existing foundations are not deep enough to support the structure above, when a basement is being created beneath an existing building, or when ground movement has caused the foundations to become unstable. It ensures the building remains safe and structurally sound throughout and after construction.

Question 47

What is mass concrete underpinning?

Accepted Answer

Mass concrete underpinning is the most common method used in residential basement construction. It involves excavating beneath the existing foundations in carefully sequenced sections — known as pins — and filling each section with concrete to create new, deeper foundations that support the structure above.

Question 48

What is reinforced concrete beam and base underpinning?

Accepted Answer

Reinforced concrete beam and base underpinning uses a reinforced concrete beam to transfer the load of the structure to a series of concrete bases. This method is used where ground conditions or structural requirements make mass concrete underpinning less suitable.

Question 49

How long does underpinning take?

Accepted Answer

The duration of underpinning works depends on the size of the building, the depth required and the method used. As part of a basement construction project, underpinning typically takes several weeks and is carried out in carefully planned sequences to maintain the stability of the structure at all times.

Question 50

Is underpinning dangerous?

Accepted Answer

When carried out by experienced, qualified contractors working to structural engineer drawings and current Building Regulations, underpinning is a safe and well-established construction process. We follow strict sequencing and safety procedures on every project.

Question 51

Does underpinning devalue a house?

Accepted Answer

Underpinning carried out as part of a planned basement construction project does not devalue a property. In fact, the additional space created typically adds significant value. Underpinning carried out to remedy subsidence can affect mortgage and insurance, but this is a different scenario entirely.

Question 52

Do I need planning permission for underpinning?

Accepted Answer

Underpinning itself does not typically require planning permission, but the basement project it forms part of may do. Building Regulations approval is always required. We advise on all regulatory requirements as part of our service.

Question 53

Can you underpin a terraced house?

Accepted Answer

Yes. We regularly carry out underpinning works on terraced houses across London. Party Wall Agreements with neighbouring properties are usually required, and all works are carried out in strict sequence to protect the adjoining structures.

Question 54

Do you carry out underpinning to structural engineer specifications?

Accepted Answer

Yes. All underpinning works are carried out strictly in accordance with structural engineer drawings and specifications. We do not deviate from the engineer's design without written instruction.

Question 55

What are groundworks?

Accepted Answer

Groundworks are the below-ground construction activities that form the foundation of a building project. They include excavation, drainage, foundation construction, concrete works and any other work carried out at or below ground level. We specialise in groundworks for basement construction projects.

Question 56

What groundworks are involved in a basement project?

Accepted Answer

Groundworks for a basement project typically include initial excavation, temporary works and shoring, drainage diversions, underpinning, and preparation of the formation level ready for the structural concrete works. We carry out all groundworks as part of our basement construction service.

Question 57

What is excavation and how is it done for a basement?

Accepted Answer

Excavation is the process of removing soil and material from the ground to create the space for the basement. For basement construction beneath an existing property, excavation is carried out carefully in sections, often by hand or with compact machinery, to avoid disturbing the existing structure.

Question 58

How is excavated soil removed from a basement project?

Accepted Answer

Excavated spoil is typically removed by conveyor, skip or mini dumper through the access point agreed at the start of the project. All material is disposed of using licensed waste carriers in compliance with current waste regulations.

Question 59

What is formwork in construction?

Accepted Answer

Formwork is the temporary or permanent mould into which concrete is poured to form structural elements such as walls, columns, beams and slabs. Once the concrete has cured and reached sufficient strength, the formwork is removed (struck) to reveal the finished concrete surface.

Question 60

What types of formwork do you use?

Accepted Answer

We use a range of formwork systems depending on the structural requirements of each project, including traditional timber formwork, proprietary panel systems and permanent formwork solutions. All formwork is designed and installed to the structural engineer's specification.

Question 61

What is permanent formwork?

Accepted Answer

Permanent formwork, such as insulated concrete formwork (ICF) or steel-faced panels, remains in place after the concrete has cured and becomes part of the finished structure. It can offer benefits in terms of insulation, speed of construction and surface finish.

Question 62

Do you carry out formwork for reinforced concrete walls and slabs?

Accepted Answer

Yes. We carry out all formwork required for reinforced concrete walls, slabs, columns and beams as part of our basement construction and structural concrete service.

Question 63

What is a concrete retaining wall?

Accepted Answer

A concrete retaining wall is a structural wall designed to hold back soil or other material on one side. In basement construction, the basement walls act as retaining walls, resisting the lateral pressure of the surrounding ground. They are typically constructed from reinforced concrete to the structural engineer's design.

Question 64

Can you build retaining walls as part of a project?

Accepted Answer

Yes. We construct reinforced concrete retaining walls for basement projects, garden terracing, boundary works and other structural applications across London and the South East.

Frequently Asked Questions

Everything you need to know

BASEMENT CONSTRUCTION

PLANNING & REGULATIONS

WATERPROOFING & STRUCTURAL WORKS

UNDERPINNING

GROUNDWORKS & FORMWORK

INSURANCE, GUARANTEES & COVERAGE

WORKING WITH US

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