Structural Engineers Homeowner Basements
Contacting a structural engineer is the first thing you need to do if you’re a homeowner and considering a basement as part of an extension or conversion. Consulting SWJ will ensure you have all the initial information you need before instructing an architect.
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Basements are increasing in popularity, and a common question is whether clients can have a basement. In this video Russell Wrapson explains the investigations needed to decide whether a basement is feasible or not.
Homeowner basements in the UK
Basements are often included in the designs for new builds as a way to add another floor or create more room on ground level. Increasingly homeowners are considering adding a basement to an existing building as an extension or part of a conversion. Basements are an excellent way to increase space and add value to a property but they pose structural challenges. You are not only designing a watertight underground room, but their creation will affect existing structures on, and around, the property.
It’s never too early to talk to a structural engineer if you are considering a basement. We will be able to complete the necessary investigations to ensure your plans are feasible before you spend any money on an architect’s designs. Even if you already have architectural drawings there will be questions that will need to be answered by a structural engineer before the design process can be completed and building work can begin.

Required steps for a basement design
There are several steps that need to be completed to ensure that the ground you are planning to build your basement in is suitable, and any existing building’s foundations are strong enough for a basement. These steps include:
1. Topographical Survey – whether a traditional excavation is possible and how the basement will fit onto your property.
2. Site investigations – these are used to assess ground conditions and establish your property’s geological sequence, the presence of groundwater, and the strength of the soil.
These are two very different surveys and you can read more about the difference between a topographical survey and a site investigation here.
Existing Structure Survey
We will also need to establish whether the existing building is able to support a basement extension. This is usually determined with a structural survey of the property establishing:
• Whether there is evidence of heave or subsidence
• If the foundations are competent enough to undergo the work required to extend downwards
Key Design Considerations
There are several regulations and standards that need to be met to ensure the completed works will be fit for everyday use such as;
• Appointment of a CESSW registered specialist to advise on waterproofing
• Drainage and waste disposal
• Ventilation points; if the basement is to be used for car parking this is key
A basement is a significant project and it is important to get the design right from the beginning to avoid problems and additional costs. A structural engineer is crucial in finding the most effective construction method to keep the basement dry and protect it from any lateral pressure from the surrounding soil. You will also need to be sure all existing local structures will not be adversely affected by the addition of a basement.
All of these factors should be considered, and budgeted for before you spend any money on architectural designs.
We are happy to answer any questions you may have, and if you live within 25 miles from Oxford we can come and complete an initial site visit to discuss your plans which may save you money in the long run.
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