One of the most underutilised spaces, often overlooked by homeowners, is the space underneath your garden or driveway. And this can be a mistake because building an underground basement extension beneath your garden can provide the biggest increase of space. From cinema rooms to guest bedrooms, spas to home gyms, the basement extension has limitless potential and won’t require a large part of your garden to be gobbled up in the process.
So, how do you go about creating an underground basement extension? In this post, we’ll be covering…
There is a multitude of uses for an underground basement. In fact, the possibilities are endless, so push your architect to get creative! Some ideas you might explore together could be...
Light wells and roof lights, which aren’t always possible with a basement conversion, can flood your subterranean garden room with plenty of natural light.
Open terrace doors and lightwells allow fresh air to reach your basement to make your under garden room more comfortable. Additionally, these openings, not always available in regular basements, provide easy ventilation to the space.
Because the room can extend as far as your property line, an under-the-ground basement can be much larger than a traditional basement conversion, which has footprint restrictions.
Under garden basements are inconspicuous and therefore, you get all the space you need without impacting your neighbour's right of light.
Given the excavation work involved, basement extensions will vary from home to home. Take a look at our step-by-step guide to get a rough idea of the processes involved, and then reach out to our team for a free tailored consultation.
Planning restrictions: Each planning office has its own policy regarding what you can and can’t do with under garden basements. That’s why it is extremely important to do your research and investigate the latest local policies and guidelines.
Conservation areas restrictions: If this is applicable, you will need to ascertain what additional restrictions may be placed on a basement development in your area. In these scenarios, a pre-application might be advised.
Measured surveys provide existing drawings, which are architectural drawings of your home as it stands today. They form the basis of pretty much every stage a project takes leading up to construction, including design, planning, building regulations, and party wall matters.
Because of the scale of your basement extension, you may need to take your measured survey one step further and commission a topographical survey, which will map out not only your home but will also give a detailed report on your terrain’s surface features and mark the contours of the land.
The next step is to start envisioning your basement and consider the key architectural and design elements, including:
These drawings will go on the form the basis of your planning application, which your architect can package up and submit to the local authority on your behalf. For extra clarity, you may also request your designer to create 3D renders/models of your basement extension. These will not only help you visualise the space better, but they can also be beneficial from a planning point of view too.
Prior to the planning application, take some time to meet with your adjacent neighbours to discuss your plans. Organising a friendly neighbourhood meeting, complete with a presentation packet with FAQs, is a great way to break the ice before breaking ground.
Communicate the following with your neighbours:
Building solid communication with your neighbours at this stage can help avoid planning issues, as well as be helpful for possible party wall matters that could arise down the road.
A full planning application will be required if you’re building a new basement or expanding it significantly.
An assigned planning officer will likely pay a visit to your home to see the proposed site. Be prepared to answer any and all questions and address concerns. The assessment process normally takes about 8 weeks, so pack your patience.
Once the project is approved, you’ll need to find a structural engineer to detail the best way to support and build your basement shell and core. The shell and core is the concrete and reinforced steel structure in the ground. The engineer’s design will factor in all survey information, timelines and budget constraints.
The structural engineer will produce a series of drawings and calculations which identify the construction sequencing, materials, steelwork, under-pinning and/or piling details, party wall detailing and Construction Design & Management (CDM) requirements.
Building regulations are a set of statutory requirements that cover everything from structural integrity, thermal performance, sound-proofing, drainage, fire safety, and more! To make sure your basement extension definitely complies with these rules, we recommend commissioning a building regulations package, which will set out all the technical details a contractor will need to know onsite - rather than relying on them to fill in the blanks themselves.
Party wall matters
Depending on the location of your extension in proximity to your neighbours, a party wall notice must be submitted to your neighbour(s) before construction begins. If the approval is not given, a Party Wall Agreement will be required. In this case, the owner of the property would be liable for all associated costs, including the neighbour’s survey fees.
There are two very distinct portions of the overall project, the shell and core and the basement fit-out, each requiring highly specialised and dedicated experts. Whilst there are a few high-quality firms that can take on both projects, for the most part, there’s a separate firm for each project.
While larger basement construction companies have extensive skills in this domain, if you are hiring a smaller firm, it is highly recommended that you hire a separate, highly experienced waterproofing design consultant.
To get a tailored breakdown of the stages involved in your garden basement extension, book a free consultation with our team.
As construction takes place, you might decide to work with an interior designer to get your decor ideas in order. Having a professional touch can help you get the most out of your new space, while they also help ensure your remaining budget goes towards the right items. However, if an interior designer isn’t for you, don’t feel like you have to rush this stage of the journey. Fitting out your basement extension can be a long-term project and we always encourage homeowners to find fittings they love, rather than just rushing out to get what’s on-trend at that time.
Money, it’s going to be a big consideration for your basement extension, so here are some costs to bear in mind…
For a cost breakdown and estimate, contact a Resi expert today. A Resi consultant will help you obtain financing if needed.
Under-garden basements can add significant value to your property - sometimes in the range of 30-40%!
However, it’s important to remember there are always risks involved when betting on the property market. What’s more, ceiling prices in your area could stop you from recouping your investment when it comes to selling. If ROI is important to you, make sure you discuss your design ideas with a local estate agent.
No other area is as tremendously full of uses and is so drastically overlooked as the space beneath your garden, yard or driveway. Whilst there are many benefits to basement extensions, under garden projects are highly specialist structures that require experienced professionals to design, waterproof and build.
Want to find out more about creating a brand new space under the ground beneath your feet? Book a call with a Resi expert today.
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