Whether you are looking to add a guest bedroom, a TV lounge, a home office or a gym, extending into your basement can be a great solution.
When people think of extending their home, they usually think up and sideways. Extending downwards could be a better solution.
There are a few things you must keep in mind when considering a basement extension. First, there is the matter of cost and complexity. Cost can vary dramatically depending on whether your basement has enough headroom to create a liveable space or not. If the project requires excavation, building cost could be as much as 40% higher. You may also need planning permission so make sure you or your designated contractor speaks with your local planning authority and building control department before any work starts. Additionally, if you are making any structural changes, chances are that planning permission will be required. This will also be the case if you are altering the facade of the property or if the building is listed or in a conservation area. If you are making structural changes and share a wall with a neighbour, you will also need a Party Wall Agreement. If you are converting an existing cellar and are not making any changes to the external appearance of the building, you are unlikely to need planning permission. However remember that planning rules are continually being reviewed and vary from one area to the next so it is always wise to check with the relevant authorities before you break ground. On the other hand, if you are sue that you will need additional excavation to create enough headroom or if you will in any way modify the façade you will almost certainly require planning permission. Planning permission will also be required if you are creating a separate unit of accommodation, if you live within a conservation area or if your property Is listed.
There is no denying that extending downwards is a great alternative to adding more space to your home. But, what about adding value? A basement extension could potentially add up to 20% value to your home. If you are creating a basement extension to add value to your home, make sure to check with some of your local state agents to confirm that this addition will indeed be a good investment.
There are some factors that could push the cost of your basement conversion. Keep an eye out for things such as having to divert drainage or if the property is in an area that has a high water table as this might mean you could need a pump to be working constantly. You also want to consider what kind of ground your property sits on. Ground such as clay, sand, marsh or made-up ground could mean additional structural work will be necessary. If your property has poor access or lacks space where excavated soil can be kept, or if you live on a street with high demand for parking and obtaining a parking permission for a skip would be difficult, costs could rapidly accumulate.
Your local authority might also require a basement impact assessment. With a rise in concerns from some home owners regarding potential water and structural damage to their homes this has become a more pervasive requirement during the planning application stage. This can be a costly and time consuming exercise, so make sure there is a budget and time allocation for it in your building schedule. Basement Impact Assessments can be carried out by a surveyor with qualifications in structural design, geology and hydrology. It is also wise to check with your local authorities what information this assessment must contain as requirements may vary.
Even if you do not require planning permission, your basement extension will require Building Regulations Approval to ensure that the extension meets health, safety and welfare conditions such as ventilation, fire safety, foundations, energy efficiency and other standards. To ensure that your project meets Building Regulation Approval you must have a set of Structural Drawings that can be submitted to the relevant authorities. Your builder, architect or planning consultant should be able to provide you with a package of plans and structural drawings produced by your structural engineer.
If you share a wall with a neighbour, and your extension will require any sort of structural change, you will also need a Party Wall agreement. This applies if you are excavating within three metres of your neighbour’s property and to a lower level than their foundations or within six metres and at an angle interesting 45 degrees from the bottom of their foundations. It will also be relevant if you are cutting holes into a shared wall to inset a beam or flashing. Party Wall Agreements are in place to protect neighbouring properties during and post construction. In most cases, this will involve serving relevant notices to the involved parties and drawing up a legal agreement and a condition survey of the relevant properties. As these can sometimes be contentious, make sure that you, your architect or consultant involves a party wall surveyor at an early stage and allocate time an budget for this.
One last thing to consider is Tanking. Tanking is the process of waterproofing your basement, and regardless of the intended use, it will be necessary. The process involves covering the walls in a special membrane to withstand water pressure from the surrounding ground. This in turn, will prevent damp or any structural damage. Make sure your contractor complies with the relevant standards.
It may seem like there are a million professionals to consult when planning a basement extension, but speaking to a reputable local builder, such as Dominant Construction who have experience of similar projects is a great place to start as they will be familiar with local planning laws and have the right experience. They should also be able to tell you which other professionals you will need to engage to create the basement extension of your dreams.