Are you looking for a basement extension?
When it comes to looking at extending your basement, there are a lot of areas to understand which may become overwhelming for you.
A basement extension can be a fantastic way to expand your living space by creating an extra bedroom, TV lounge, office or gym.
This blog by Windsor Bespoke will take you through everything you need to think about, from how much it’s likely to cost down to whether or not you will need planning permission.
Should I Convert My Basement?
- The costs and complexity of the project will vary dramatically depending on whether you have an existing cellar with enough headroom that can be easily converted or whether you will need to excavate to make the space workable.
- Speak to your local planning authority and building control department before you start any work to make sure you know exactly what permissions are required.
- You will almost certainly need planning permission if you are making any structural changes or altering the external appearance of the property, if the building is listed or in a conservation area.
- If you are making structural changes and share a wall with your neighbour you will need a Party Wall Agreement.
Do Basement Conversions Add Value
If you are settled in your home but have outgrown your living space, building an extension is a great way to make more of what you’ve already got.
Adding an extra room, such as a converted basement, can increase your property value by up to 20 per cent.
We recommend you speak to a couple of local estate agents before you start if this is your primary motivation; they will be able to indicate whether you will recoup your investment when it comes to selling.
A good source of natural light and decent ceiling height will help to ensure that your conversion is a worthwhile investment that boosts your home’s value.
How Much Does A Basement Conversion Cost
We asked the Basement Waterproofing Association to provide up-to-date estimates for the likely costs involved in different types of basement conversion projects, from the basic to the more complex:
| PROJECT TYPE | COST ESTIMATES |
|---|---|
| Conversion of an existing cellar | £900 – £1,400 per square metre |
| Lowering the floor level and underpinning an existing cellar | £1,500 – £2,000 per square metre |
| Digging a new basement space underneath the building and underpinning | £2,500 – £3,000 per square metre |
| Digging a new basement space underneath a garden | £1,500 – £2,000 per square metre |
| Creating a light well or external access | £5,000 – £7,500 per square metre |
| Architect/ surveyor/ planning consultant’s fees | £1,500- £3,000 each (but you may not need all three) |
| Planning application council fees (if required) | £206 (householder application) £462 (if new unit of accommodation is proposed) |
| Building Regulations application | At least £750 |
| Party Wall agreement (if required) | At least £700 per neighbour |
| Additional tax if using VAT-registered contractors | +20% |
Other factors that might push up your basement conversion costs:
- If you have to divert drainage or if the area has a high water table which means you need a pump to be working constantly.
- Your property sits on certain types of ground such as clay, sand, marsh or made-up ground (also known as fill or man-made ground, this where ground levels have been altered or filled in using building waste and previously excavated material.)
- The site is difficult to access or has nowhere to store excavated soil.
- There is high demand for parking on your street and you can’t get permission for a skip.
Does my basement extension need Building Regulations approval?
Regardless of whether you need planning permission or not, you will almost certainly still require a building warrant to ensure that your conversion meets a minimum standard of health, safety and welfare conditions; this covers areas such as ventilation, fire safety, foundations, energy efficiency and other standards.
It may seem like there are an overwhelming number of professionals to consult when it comes to planning a basement extension, but speaking to a reputable local builder with experience of similar projects is the best place to start.
If they are familiar with local planning laws and have the right experience, they should be able to tell you which other professionals you will need for the job.
Do I need a Party Wall agreement?
If your basement extension requires structural changes to the building, such as excavation, you will likely require a Party Wall Agreement.
Some of the main criteria for requiring a Party Wall Agreement include:
- Excavating within 3 metres of your neighbour’s property and to a lower level than their foundations.
- Excavating within 6 metres and at an angle intersecting 45 degrees from the bottom of their foundations.
- Cutting holes into a shared wall to insert beams or flashing
Party Wall Agreements aim to protect neighbouring properties during and post construction and in most cases will involve a the serving of relevant notices to neighbours, a legal agreement and a condition survey of the relevant properties.
This can sometimes be a contentious issue with your neighbours, so you should ensure that you contact a party wall surveyor at an early stage, or speak to your architect or consultant, in order to ensure that time and cost provisions are made for this.
How high does the ceiling need to be?
Even though Building Regulations do not specify a minimum height for ceilings, 2.4 metres is a good finished height to aim for.
You will need at least 2 metres over the stairs to keep within building rules. Don’t forget that you will need to include space for the height of your flooring within your calculations.
What is basement ‘tanking’ and is it necessary?
“Tanking” is another word for the process of waterproofing your basement and will be necessary whatever you are planning to use it for.
The process involves covering the walls in a membrane or another material to withstand water pressure from the surrounding ground, preventing damp and structural damage.
Contact Windsor Bespoke
If you are looking to convert your basement then get in touch with us today on info@windsorbespoke.com
We have an architect that deals with all planning permission and building warrant applications for the relevant councils.
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