Basement Construction: A Comprehensive Overview

Basement construction has become increasingly popular in the UK in recent years, especially in large cities where space is scarce and expensive. Homeowners across the country are embracing the potential rewards of building a basement to increase the square footage of their property and add value to their homes.

If you’re about to embark on a basement construction or you’re still pondering whether to convert your basement into a living space, then you’ve come to the right place. The following comprehensive guide will explore everything you need to know about adding a basement to your property. Whether you’re looking to add a home theatre, a nice wine cellar or a cosy guest bedroom under your home, this guide will help you navigate the process smoothly and make informed decisions along the way.

Suitability and Potential Challenges

Before you begin construction, it's crucial to conduct a thorough site assessment to identify if your property can withstand excavation and if any potential challenges might arise as a result of specific ground conditions. 

Potential challenges that might impact your basement construction include:

• High water table soil. This is the level at which groundwater rises to the surface. If the level is high, the resulting water pressure can exert immense force on the basement walls, potentially leading to cracks and leakage. If you identify this as a potential issue during your site assessment, then you will need to install specialised waterproofing measures and drainage systems to effectively manage water intrusion.
• Sloping sites. If your property is on a slope, then you will need to determine whether the soil is suitable for a basement construction. This is important because the lateral pressure exerted by sloping ground can put undue stress on your basement walls. You will probably need additional structural reinforcement or grading to overcome this issue.
• Unsuitable bedrock. Hard, solid bedrock can provide a stable foundation for your basement. Soft or unstable bedrock, in turn, may require additional structural support.
• Existing structures or services. This might include neighbouring buildings or underground utilities. It’s important to identify and map out all pipes, cables and septic tanks in advance to avoid damage or service disruption.
  
  

Types of Basement Constructions

Once you determine if your property is suitable and you address any identified challenges related to ground conditions, the next step is deciding which type of basement would work best for you. 

Generally speaking, there are three types of basement construction:

• Poured concrete basements are the most common method for building basements. With this type of basement, concrete is poured into temporary formwork before reinforced steel bars are incorporated into the concrete to enhance its structural integrity. Poured concrete basements offer excellent strength, durability and waterproofing capabilities, and they are suitable for a wide range of soil conditions and groundwater levels. 
• Precast concrete basements use prefabricated concrete panels that are assembled on-site. These panels are usually placed on concrete footings and connected through welding or bolting. This method offers faster construction times, and it is often more cost-effective compared to a poured concrete basement. However, joints between the panels must be properly sealed to prevent moisture from penetrating the basement interior.
• Block masonry wall basements are another cost-effective and time-efficient alternative to poured concrete, particularly for smaller-scale basement constructions. With this method, concrete blocks, typically made from cement, sand and gravel, are stacked together and mortared into place. This method is often used for shallower basements or in areas where precast panels are not readily available. However, it’s essential to consider the condition of the soil before committing to this method. If the area is prone to soil swelling then the additional pressure can weaken the joints of your structure, potentially compromising the structural integrity of your basement. 
  
  
  

Basement Excavation

Excavation creates the underground space you need for your new basement. During the process, your building contractors will remove soil, rocks and other debris to the desired depth and dimensions. They’ll start by erecting a temporary protection barrier, known as hoarding, around the excavation site. They will also construct a timber shelter to protect the site from the elements. 

Once the groundwork has been laid, your team of builders will use a backhoe or excavator to remove soil from the site. As they get deeper, existing foundations may require underpinning to ensure their stability and integrity. At this stage, your construction team will also re-route any existing building services, such as plumbing pipes or electrical lines, to make space for the excavation.

Waterproofing and Drainage

Waterproofing and drainage are essential for preventing water from seeping into your basement so you can create a dry basement environment. There are several waterproofing methods that you can use, depending on the specific conditions of your land.

These methods include:

• Interior waterproofing. This involves applying a waterproofing membrane to the inside of the basement walls and floor. The membrane can be made of a variety of materials, such as polyethene, vinyl or cementitious.
• Exterior waterproofing. This involves sealing the outside of the foundation walls and the surrounding soil. This can be done by applying a waterproofing membrane or installing drainage pipes or a French drain.
• Sump pumps. A sump pump is a device that collects water from the basement and pumps it to the outside. Sump pumps are essential for preventing water from backing up into the basement, especially during heavy rain or flooding.
• Vapor barriers. This is a sheet of plastic that is installed between the basement walls and the insulation. This helps to prevent moisture from entering the basement from the ground.
• Drainage systems. A drainage system is a network of pipes that collects water from the surrounding soil and directs it away from the foundation. This helps to prevent water from pooling around the foundation and seeping into the basement.
  
  
  

Basement Flooring Options

Once the foundation is laid and waterproofed, the next step in the basement construction process is installing your floors. Most builders recommend using inorganic materials like tiles, polished concrete or vinyl rather than organic materials like hardwood, as they are more resistant to moisture and humidity. 

Insulation and Ventilation

Because basements are located underground and away from the elements, they tend to be good at maintaining stable temperatures throughout the year. However, there are still steps that you should take to optimise insulation and prevent moisture issues. This includes installing foam insulation, rigid insulation boards and fibreglass batts.

You also need to take measures to optimise ventilation during the basement construction process. This is crucial as you won’t have any windows for natural ventilation in an underground space. The best option here is to install a mechanical ventilation system that continuously exchanges stale indoor air with fresh outdoor air.

Lighting

Finally, the lighting you pick for your basement will have a direct impact on the ambience and overall feel of your space. Proper lighting can make a basement feel more spacious, inviting and functional, while the wrong lighting can make it feel dark, dingy and uncomfortable.

Common artificial lighting options for basements include recessed lights, ceiling lights, sconces, floor lamps and track lights. Alternatively, LED lights can be an energy-efficient choice, offering long lifespans and low heat generation. You can also introduce natural light through light shafts or walk-on glazing, providing a connection to the outdoors and enhancing the overall look and feel of your new basement construction.