How Basement Waterproofing Works?

Given that the basement is prone to experiencing levels of water pressure due to the accumulation of water in the surrounding ground and soil, it’s not surprising that this pressure can result in cracks, leaks, and dampness issues. By applying the correct waterproofing solution you can prevent water from seeping into your basement.

To transform your basement into a functional space below your home, we offer three solutions. The first is tanking, which forms a watertight barrier to prevent moisture penetration. Another option is installing proofing solutions during the construction phase of the building. Lastly, we have a Cavity drain membrane solution that utilizes a combination of membranes, drainage channels and pumps to redirect water from your property. We can also tailor a solution by combining systems for the best results.

Ways to Waterproof Your Basement?

In the Basement waterproofing industry people often talk about the three systems, namely type A, B, and C. It’s worth noting that a combination of these systems might be utilized to ensure the best and most effective solution for your basement or cellar. The final decision on which system suits your needs will be determined after a site inspection conducted by one of our surveyors.

Type A Waterproofing – Barrier System

This is where a physical barrier is used to protect the basement or cellar walls and prevent water from getting in. Type A waterproofing, commonly known as “Tanking ” involves applying membranes, waterproof cement, or a slurry, to the walls below ground level. For new basement constructions, Type A external waterproofing applies the tanking barrier membrane. Slurry, to the outer wall of the structure, preventing groundwater from entering. During building renovations or after construction, Type A waterproofing can be installed on the basement walls.

Type B Waterproofing – Integrated Systems

This pertains to the waterproofing solutions that are incorporated into the building structure during the construction phase. Typically Type B waterproofing includes using reinforced concrete and implementing a water control mechanism to prevent any water seepage through construction joints (like a hydrophilic waterbar). It is important to involve our team of waterproofing specialists right from the initial design stage of your project if you wish to have a Type B system installed on your property.

Type C Internal Waterproofing

This method is considered the most up-to-date technique for waterproofing a basement or cellar. It involves combining a waterproofing membrane, basement floor drainage, and a sump pump to effectively and securely remove any water. To create a dry internal surface Cavity Drain Membranes utilize a studded membrane that lines the walls and floors.

Afterward, the walls can be dry lined or Plastered, while the floors can be screeded or overlaid with materials like waterproof floorboards or tongue and groove flooring. Sealed systems are used in conjunction with either a cavity drain system or a sump pump when dealing with water or flooding. On the other hand ventilated systems are used in situations where there is no water and when traditional damp-proofing methods are not suitable. Both of these systems can be designed to comply with BS8102, which is the code of practice governing waterproofing structures.

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Building a Strong Backbone: Structural Design and Calculations
Think of the structural design and calculations as the skeleton of your basement conversion. They keep everything upright and in place. The stage starts with:

Hiring a Structural Engineer: Let’s start by appointing an expert basement structural engineer in London. These are the experts who’ll tell you the best way to design, support, and build your basement’s ‘shell and core’ (that’s a fancy term for the reinforced concrete structure in the ground).
Incorporating Survey Information: With the survey data in hand, the engineer will create a design that’s a perfect fit for your property’s characteristics.
Creating Drawings and Calculations: Next, your engineer will get to work on a set of drawings and calculations. These are your roadmap, outlining everything from the construction sequence, materials, steelwork, to underpinning or piling details, and party wall detailing. The engineer will also lay out the rules of the road in terms of Construction Design & Management (CDM) requirements.

The structural design is the key that unlocks the next stage of the process. It’s the detailed plan that shows how your basement conversion in London will come to life. And it’s not just for your benefit – it’s also required for the next step, the Party Wall Agreement. The surveyor you appoint will need to take a close look at these plans for your Award. 

Structural Design: The Foundation of Your Basement Conversion
The structural design is the actual foundation of your basement conversion project. It outlines the technical details of how your basement will be constructed from the ground up. The structural design engineer will ensure the basement is structurally sound and complies with all necessary regulations.
Once the technical and structural design is done, we move on to the Party Wall Agreement. Each stage and step is crucial to ensure your basement conversion is a success.

Why is a Structural Engineer necessary?
To obtain approval from Building Regulations, it is necessary to have an engineering design in place. Failing to do so could result in the devaluation of the property in the basement area. The structural design plays a vital role in this process as any errors or miscalculations could lead to damage not only to your property but also to neighbouring properties.

What can I expect the structural engineer to provide and/or guarantee?
The structural engineer should be able to create designs and drawings that comply with the requirements of Building Regulations for the structure and construction. Based on the experience of the engineering firm, an engineer may possess the expertise to deliver a design that meets all aspects of Building Regulations, enabling the construction of all relevant components.

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A Desirable Space Solution

London’s real estate market is constantly evolving with a demand for space, homeowners are seizing the chance to enhance their property value by extending downwards. By converting basements into stylish spaces there is potential to transform previously unused square footage into prime living or working areas.

A Lucrative Financial Outcome

Basement conversions in London can indeed lead to gains. According to experts in the industry, a well-planned and executed basement conversion can increase your property’s value by 10 20%. Considering London’s already soaring property prices this percentage represents a boost.

Considering Investments

However, embarking on a basement conversion project involves more than focusing on the value. It’s a decision for homeowners to consider factors such, as construction costs, legal permits, and design complexities. In the heart of London, the cost of converting a basement can vary depending on factors like the size and complexity of the project. So it’s important to analyze the investment potential to ensure a return on investment (ROI).

Catering to Market Trends

One overlooked aspect is tailoring the conversion to meet market demands. This could involve creating a home office that caters to the growing trend of work or designing an extravagant leisure area complete with a home theater and wine cellar. Aligning your basement conversion with market demands can significantly boost its ROI.

Embracing Sustainability; An Added Benefit

Today buyers are increasingly interested in energy-efficient homes. By incorporating eco features into your basement conversion you not only reduce your carbon footprint but also enhance the property’s appeal in the market and consequently increase its ROI.

The Importance of Expert Guidance

To fully unlock the ROI potential of a basement conversion in London it is crucial to partner, with experts who understand both the market intricacies and technical aspects involved in projects. Their guidance can streamline the process prevent mistakes and maximize your investment returns.

In conclusion, embarking on a basement conversion in London is an opportunity that holds the potential for increasing the value of your property and meeting the demands of modern living. It’s not about gaining space but also about unlocking possibilities and seeing your property become a profitable asset.

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At New Build Contractors, we advise our customers to take into account the following:

Builder Company Guarantees: This is the guarantee from the London basement conversion builders that the work undertaken will be free from any defects for the stipulated period. If any issue arises within this timeline due to poor workmanship or poor materials, the builder will be obliged to fix the problem at no extra cost.

Waterproofing Guarantees: These are usually divided into three categories, starting with:

The Design Guarantee: This covers the waterproofing design, ensuring it’s fit for purpose.

The Product Guarantee: This covers the waterproofing materials used in the basement construction, assuring that they’ll perform as expected for a certain period.

The Installer Guarantee: This guarantee is from the installer, assuring that the waterproofing system has been installed correctly.

Insurance Backed Guarantees (IBG): An IBG is an insurance policy that provides cover if the original contractor ceases to trade and is, therefore, unable to honor their guarantee. This could be due to any reason such as bankruptcy, liquidation, death, or retirement.

Latent Defects Insurance: This is also known as structural warranty insurance. This covers the cost of remedying structural defects that become apparent after the completion of the basement building project. These are defects that were not detectable at the time of completion and take time to appear on the surface.

Building’s Renovation Insurance (Joint Names): This is the type of insurance taken out by the builder and the client together. It will cover the client and the contractor for any loss or damage to the works and site materials during the period of renovation. 

Each of the above forms of protection plays an important role in managing and deterring the potential risks involved in a basement conversion project. Always ensure that the necessary coverages are in place before beginning any

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Define the Basement’s Purpose – What is the purpose of your basement and the unique requirements you have? If you want to bathroom, you need to think about the plumbing, drainage, waterproofing, and ventilation. For a home cinema, you will need to take into account the room’s acoustics, install a stepped floor to optimize viewing angles, and fit dimmer switches to create the perfect visual mood. The possibilities are endless for a finished basement in London.

Determine your Ceiling Height – Ceiling height is a vital consideration for basements, not only for building regulations compliance but also for your comfort. When deciding the height of your ceiling, do not forget any ductwork or piping that may run through and reduce the open spaces vertically. 

Create a Basement Floor Plan – Basements can often feel quite cramped. To maximize the space in your basement effectively it’s important to plan thoroughly. Think about how you intend to use the space, what the most common traffic patterns will be, and which parts of the room should be easily accessible. This plan will help you devise a functional layout. Check with your local building authority on how much space you will need to allow for a window that can be opened and climbed out in any case of emergency evacuations. 

Create Basement Zones – The finished basement needs to be split into different zones. Depending on what the purpose of your basement is, you can partition it to create a high-level structure which allows for a better understanding of how the space flows and where fixtures and fittings should be logically placed.

Factor the Storage Needs – Basements are more than often used as storage spaces even when their primary function is something else. Basements usually have a lot of wall space to utilize so we suggest using this to your benefit. You can use the space to install wall-to-wall cupboards and closets, or floating shelves along the walls. Make sure that your basement design facilitates all of the storage you need. We also suggest to look under the stairs as a great spot to add some much-needed storage.

Consider Lighting –  Basements are often challenging when it comes to getting light due to their submerged structure. When designing your basement in London, it’s important to consider how to make the most of daylight through windows and even outdoor landscaping. Additionally, the design plan should incorporate lighting options, like recessed lights or individual fixtures considering that basement ceilings tend to be lower and hanging fixtures might not be suitable.

Select an Interior Design Style – To effectively merge all the factors to consider when designing the layout of your basement floor plan it is beneficial to have an interior design style in mind. For example, selecting the lighting should align with your choice of wall colors. 

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1. Roof lights and light wells; It’s important to have these in place to allow light into your basement improving its atmosphere and livability. 

2. Windows, both internal doors; The choice of windows and doors can greatly impact energy efficiency, security, and the overall aesthetics of your basement.

3. Staircase, floor, and wall finishes; Opt for finishes that are durable moisture resistant, and complement the design of your home.

4. Sanitary ware, tiles, and paint colors; These elements play a role in creating a look throughout your basement.

5. AV (Audio Visual) security systems IT networks; Make sure you plan for installations such, as visual equipment, security systems, and network access points.

6. Heating, Ventilation, Air Conditioning: You will need to plan on how you will heat, cool, and ventilate your basement to maintain comfort and avoid moisture and damp build-up problems.

7. Light fittings and furniture selections: Your overall design theme, personal style, and budget will also determine these selections.

You can hire a professional interior design company to give your basement a nice design and an efficient project flow too. Interior designers can help in creating a cohesive design scheme and advice on certain product selections too. Given the number of products, materials, and finishes that are required to be selected, an experienced interior designer can make the process easier and help you avoid any unforeseen issues. 

Do remember that when hiring an interior designer, check that they have the technical knowledge within the basement construction sector. They should be experienced in understanding all the technical details and designs such as lighting plans, floor layouts, and more. If possible tell them to create a CAD package of drawings and detailed specifications which will allow us as the building company to get clear instructions when building your basement.

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Excavation and Construction of the Concrete Box
Once all preliminary tasks have been completed we can finally begin with the basement construction work. This stage involves excavating the basement area and creating the structure commonly referred to as a ” box.” Basement Conversion London ensures we follow the build to your design specifications. We ensure that all work strictly follows the approved design and avoids any modifications as that can lead to issues down the line. 

At a level here are the main steps involved in the construction process;

Excavation; After confirming that the site is safe and ready for construction Basement Conversion London’s team will start digging out space for your basement. We undertake this task with care to avoid any damage, to your house foundation or nearby structures.

Foundation work; If it is required, we may need to underpin your foundation to handle the weight added by having a basement.  To evenly distribute the weight of the building this process involves extending the foundation either in depth or breadth.

Constructing the basement; Once the area is prepared, we start building the concrete structure of the basement. This forms what we refer to as the “shell” or the basic structure of your basement. 

Waterproofing; Once the shell build is complete, we take measures to waterproof it and prevent any moisture from seeping into the basement. This includes applying specialist waterproofing materials to the walls and installing a drainage system if needed.

Inspections; Throughout these stages, your Building Control Inspector will conduct inspections to ensure that all work is being carried out in accordance, with approved plans and regulations.

Remember, maintaining communication with your contractor during this process is crucial. Keeping a line of dialogue will help resolve any issues or questions that may arise promptly.

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We’ve noticed that every basement project in London has resulted in some degree of damage (minor) occurring even when the projects were well-designed, effectively managed, and properly constructed. The nature of work is invasive and building issues are bound to arise. This extract from BBC Inside Out demonstrates the type of damage that can occur.

What do we suggest? 

Before you start any basement construction work it’s important to engage in discussions with your neighbors regarding the party wall. We can also guide you if your neighbor plans to carry out a basement excavation.

This is because if there is no connection between your property and your neighbors the Party Wall etc. Act 1996 mandates that you serve an Adjacent Excavation Notice under section 6 of the Act when you dig within 3 meters of your neighbor’s property and go deeper, than their foundations.

Considering the complexity involved in constructing basements we highly recommend involving a Party Wall Surveyor at the initial stage to gather information and communicate effectively with your neighbors.

Do I need a Party Wall Surveyor?

If your basement is not in a detached property and if any excavations are within three meters of another property, you will require a Party Wall Agreement. In this case, it is important to hire a party wall surveyor with expertise and experience in dealing with basements.

To proceed with the Basement project, it is crucial to gather all the right information:

1. Ensure you have all the basement calculations and engineering drawings for the works. In some cases, these can be prepared while dealing with Party Wall matters.

2. Obtain drawings to have an understanding of the project.

3. The significant document you’ll need is the works information, which outlines how the basement excavation will be carried out. This is crucial because neighbouring properties are at risk during this phase of potential Party Wall extensions.

4. Verify soil conditions by examining borehole and trial hole data.

5. It’s important to secure funds for any expenses that may arise due to damages caused by the works on neighbouring properties. This can be done by setting aside money in an escrow account, which will cover any work if required.

6. This situation often arises when undertaking high-risk projects, particularly when neighbouring properties have already undergone their construction work, like loft conversions involving Party Walls. We suggest engaging a Surveyor to protect your interests and calculate funds, as the escrow account is essential.

If any damages are discovered after the completion of the works, the Party Wall Surveyor will examine them and come to an agreed-upon financial arrangement. This agreement serves as a binding document for all parties involved.

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Types of Surveys Required for Basement Conversion

Before commencing your basement conversion project you will typically need to complete the following surveys;

1. Soil Structure Survey; This survey examines the composition of the soil at the desired excavation depth. Identifies any concerns related to the water table level. This information is vital to ensure a stable basement construction in London. More information about Soil Surveys.

2. Drainage Survey; This survey determines the location of drains around or beneath your property and garden. Understanding this helps assess how the basement construction might impact your existing drainage system. Depending on drain placement you may require an agreement from your water utility provider known as a “build over” agreement. Read more about the Drainage survey here.

3. Site Dimensions Survey; This survey provides measurements of your property which are essential for designing and planning your basement conversion effectively.

4. Tree Assessment Survey; This survey examines any trees in both your garden and neighboring gardens to evaluate their susceptibility to damage during excavation, for the basement. To proceed with your basement conversion, in London, it’s important to consider any trees that may be subject to a Tree Preservation Order. Here is a great article by Crown Tree about Tree surveys. 

Additionally, it is crucial to conduct a Flood Risk Assessment for your property. This assessment will evaluate the flood risk. Greatly influence the design and construction of your basement conversion.
To lay down a foundation for your project these surveys play a role. The insights gained from these surveys directly impact the planning, design, and execution of your basement conversion. By conducting these surveys upfront you can proactively address any challenges that may arise.
Remember that starting with knowledge sets the path to success. Conducting accurate surveys is a step, towards ensuring a seamless and hassle-free basement conversion. It is always advisable to seek guidance during this process.

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Several factors can influence the cost of a basement conversion;

Type of Project: Converting an existing basement tends to be less expensive than excavating a new one:

• Size of Conversion: The overall cost increases as the basement area grows.
• Intended Use of the Basement: The purpose of the conversion impacts the level of renovation required. For instance, utility basements have requirements compared to living spaces, which affect costs.
• Material Quality: Opting for quality and durable materials will raise expenses.
• Basement Condition: If the basement is in a bad condition, extensive work will be needed, leading to higher costs.
• Finishing Touches: Allocate funds for decoration and flooring to complete your transformation.

Cost Breakdown by Type of Basement Conversion

Standard Cellar Conversion; Converting an existing basement typically incurs costs compared to constructing a new excavation site. The typical cost, for each meter is approximately £1,600 to £1,800. 

If you have a home in Central London there’s a chance it already has a basement. Converting these basements into spaces usually comes with a price tag of around £1,600 to £1,800 per meter which is similar to what you would expect for other types of properties.

When it comes to remodeling basements the costs can range from £1,000 to £1,800 per meter. The final cost depends on factors such as the size of the basement, excavation requirements, waterproofing needs, and the types and quality of materials used.

To accurately estimate the cost of converting your cellar into space it’s important to consider these aspects;

• Size and Scope; Evaluate the size of your basement or cellar. Determine how much excavation work will be needed.
• Purpose and Materials; Decide how you plan to use the space and factor in the costs associated with materials required for that purpose.
• Additional Work; Include expenses related to work plumbing installation, plastering, painting, decorating, as well as fixtures like lighting or bathroom fittings.
• Expert Advice; To get an accurate quote tailored to your project’s specific needs and requirements consult with local basement specialists like us who can provide professional guidance.

Considering these elements during your planning phase and understanding them all will enable you to create an effective budget for your basement conversion project.

Bottom line

The total cost of a basement conversion depends on factors, such as size, complexity, and any unique custom features like a swimming pool. On average basement conversion London prices a basement extension at around £150k – 200k (+VAT). This estimate includes components such as soil excavation volume, floor-lowering requirements, architectural and planning services, material costs, and more. All these elements collectively determine the price of a basement conversion.

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