Building a basement in your house is always a worthy investment. You can turn the space into a bedroom, storage, or your very own private sojourn. However, if you’re living in the UK, then you might know that building a basement in your house is a luxury. Reason?
In the UK, most houses are constructed directly onto concrete slabs. These shallow slab foundations are installed directly into the ground to provide a cushioning effect against the water table. The results show significantly reduced construction prices relative to properties with deep foundations.
Guess what the drawback is? You cannot build any basement. That’s a big compromise UK resident have to make while building their homes. But if you’re wondering if there is a solution to building a basement in a way that is safe, watertight, and relishing to live in, then you’re at the right place. We’ll guide you about everything related to constructing comfortable basements under your existing UK homes.
Your Roadmap to a Perfect Basement
Step 1: Pre-Construction Approvals
- Apply for planning consent from the local authority if the build goes beyond permitted limits
- Secure Building Control approval to ensure the structure meets safety standards
- Hire a Party Wall surveyor if neighbouring properties are impacted
- Arrange for ground surveys and have a structural engineer provide detailed calculations
Step 2: Foundation & Base Preparation
- Outline the basement zone, leaving at least 0.6–0.9m space to work around.
- Dig in layers and install shoring where depth exceeds 1.2m.
- Scan the ground with a CAT tool to detect hidden pipes and cables.
- Firm up the formation ground, then spread a 150–200mm hardcore layer.
- Apply sand blinding (50mm) and cover with DPM for protection.
Step 3: Main Construction Phase
- Install continuous insulation (100–150mm PIR boards) for thermal performance, especially for basement walls.
- Cast a base concrete slab (C25/30) using A393 mesh for strength.
- Construct surrounding walls with reinforced concrete, concrete blocks, or durable engineering bricks.
- Apply a uniform 50mm concrete coating over the reinforcement.
- Fit continuous insulation (100–150mm PIR boards) around basement walls to improve thermal efficiency.
Step 4: Utility & Service Fittings
- Apply approved structural waterproofing and drainage systems (Type A, B, or C as per BS 8102).
- Secure the interior spaces by fitting a cavity drain membrane.
- Cover service entry points using water-resistant compounds as part of the water management system.
- Include a radon protection barrier if required by the local environmental regulations.
Step 5: Stairways & Entrances Setup
- Install electrical wiring compliant with BS 7671 (18th Edition).
- Fit a mechanical Ventilation with Heat Recovery (MVHR) system.
- Add drainage with a sewage pump where levels fall below the main sewer.
- Construct either a suspended floor or a 150mm reinforced concrete slab.
Step 6: Interior Completion and Access Points
- Create stair openings with adequate structural reinforcement.
- Install an external basement door complete with a weather-sealed threshold.
- Apply a sand and cement render (3:1 ratio) to the basement walls.
- Lay a 65mm floor screed with a protective moisture barrier underneath.
- Install moisture-resistant plasterboard with a skimmed finish.
Final Step 7: Backfilling & Landscaping
- Refill soil in 300mm layers using granular material, compacted to 95% density.
- Install land drains and surface water management systems.
- Add a protective apron at the basement entrance for durability.
- Apply render to any exposed concrete surfaces.
Construction Timescales for UK Basements
- Every stage of the construction should comply with Building Regulations 2010 and BS 8102.
- Builders usually take 4–8 weeks to complete the basement construction.
- You require professionals to build a basement. These include certified specialists, such as CHAS-approved contractors or ICS-certified engineers.
- You need to protect your investment by updating insurance and warranty for all your construction projects.
Tips for Successful Basement Construction in London
Basement construction is usually quite an expensive job, especially when you’re excavating below the current structure. So, you need to take some measures while building your basement in London. Here are some key steps you can take:
- If a company offers an unrealistically low quote, be cautious about choosing it. This signifies that the company didn’t consider any mitigation against risks while calculating the basement construction costs.
- Ensure that the company you hire has the necessary experience and technical expertise. For this purpose, you need to review their portfolio and obtain references.
- A construction method statement must be prepared in advance to describe all the details of how the basement will be constructed. It should include H&S and temporary support solutions.
- The entire construction process should be overseen by an on-site structural engineer, particularly during excavation and shell creation.
- You need to obtain a waterproof guarantee upon completion of the work.
- A building regulation certificate must be obtained to ensure that the construction of the basement was carried out in accordance with regulatory standards.
Start Your Basement Project Today by Reaching Us Out!
Reading out the critical basement construction underneath your current house in the UK might give you an idea that it’s not impossible to do this job. What makes this work difficult is that you’ve to cover all the essentials to carry out this job perfectly.
But here’s the catch. You can always reach out to WJB Groundworks for their professional basement building services. With extensive industry experience, WJB Groundworks is your go-to construction partner for building cosy, spacious, and luxury-driven basements under your existing houses in the UK.
We guarantee safety, reliability, and high-quality outcomes for all our construction works – a testament to the confidence in our high-standard services. Reach out to us today at 0744 688 6409 or e-mail info@wjbgroundworks.com to get your very own basement under your existing house in the UK.
