Knowing how to plan a basement addition is the next logical step for homeowners hoping to create more living space. If you’ve exhausted opportunities to add above-ground space, whether that’s via a kitchen extension or a loft conversion, a new basement offers a smart solution.
Basement ideas can be used if you already have an unfinished basement or basement, or you don’t have anything dug there at all. If you already have a basement, one option is to extend outward on two sides of that area and dig down another 1.6 feet or so to make room for the utility room, or something similar. If you want to discover a new underground level, regardless of whether you already have an existing vault, you will be excavating from scratch.
A basement typically occupies about 50 – 65 square feet, while a new basement can offer more than 330 square feet and make room for an additional family room, kitchen or bedroom. However, there are a number of aspects to consider before moving forward.
How to plan to add a basement
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1. Cost vs Reward Evaluation
Basement extensions aren’t cheap. We are currently working on figures of around £1,800 per square foot. “There are a lot of variables that affect this cost – excavation depth, ground conditions, level of fit-out, and so on,” says Daniel Adeshile of design studio Ade Architecture. Digging a basement is much more expensive than expanding elsewhere, so it’s worth exploring above-ground options first. On tight sites, this is often not an option, so we need to drill down to create the required space. With this extra cost, you have to consider whether this is a good value. Will the cost of the business be reflected in the resale value of the property?
2. Evaluate the suitability of the project
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Homes can be made unsuitable for a basement for many reasons. “This could be a result of local planning policy that places restrictions on the establishment or size of basements, or things that happen underground nearby that may affect development, such as proximity to major sewers or underground tunnels,” Daniel says. Basic details to check before you begin include the proximity of your home to pipelines, storm drains, and sewers.
3. Orientation as a geotechnical survey
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There are many assessments that need to be done before construction on the basement begins. “The first is a geotechnical survey that looks at ground conditions around your home,” Daniel says. Next, you will need a utility survey. Your architect will also need a measured survey of the house and the area around it. The final evaluation will be an asbestos survey, which your contractor will organize.
4. Get permission – which is not always necessary
Subterranean development is possible under the Permitted Development (PD), which means you don’t have to apply for planning permission. “However, for your project to fall into this category, you can only build within the space of your home—you can’t have anything that changes the street scene,” Daniel says. “If you’re introducing new light in the front, back, or side of the house, you’ll need to get full planning permission.”
To apply for planning permission, you will need to submit a set of current and proposed drawings. “When it comes to hiring an architect to put your design proposal together, I recommend using a registered professional,” Daniel says. “Going through a pre-planning process with the local authority is the best way to gauge whether your application will be positively accepted.”
5. Consider the exchange
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As with all small addition ideas, waterproofing and drainage are the main technical aspects to follow when wondering how to plan a basement addition. “Installing a large enough sewage pump is vital,” Daniel says. If it rains a lot and the sump pump isn’t big enough, you’ll have a flooded basement. Fire safety is also key. One way to meet building regulations is to incorporate sheltered passages to exit the lower ground floor in the event of a fire. If the design is open, then the installation of a sprinkler system is an alternative. We often also encourage customers to fit a mechanical ventilation and heat recovery (MVHR) system to ensure a supply of fresh air.
6. Planning for natural light
It is important to flood the space with natural light – lighting is often the optimal solution. You’ll also want to ensure good floor-to-ceiling heights. We encourage our clients to create a height equivalent to what you find on the ground floor, so usually 9 to 10 feet. Another aspect to consider is the connection of the lower ground floor to the rest of the house, as well as the garden. Incorporating a vacuum from the ground floor to the basement, so that sunlight can seep through, works well.