Basement Conversions


A basement or garage conversion/remodel can be a great way to add extra living space to your home if your options for a rear/side/loft extension are limited or if you don’t want to drastically change the exterior appearance of your home.

There are two types of basement conversion:

  1. Turning an existing basement/garage into a usable living space
  2. Excavating a new basement

How much does a basement conversion cost?

Build Cost
Turning an existing basement/garage into a usable living space costs from £700 per square meter

Other Cost Factors

  • Will you need to move your boiler/consumer unit/gas meter?
  • Will you need to underpin (reinforce existing foundations)?
  • Will you need to lower the floor to increase ceiling height?

Excavating a new basement under an existing house will cost from £2000 per square meter

Other Cost Factors

  • Do you need any Party Wall Agreements with your neighbours? (Covers shared walls/structures and protects both yourself and your neighbours whilst work is being carried out) Budget from £700 to £1,000 per neighbour
  • Do you need a Build Over Agreement? (If you’ve got a shared drain running across the back of your garden and you’re going to build over it or within three meters proximity) Budget around £335
  • Does your home have solid concrete or timber sub-floors?
  • How easily accessible is the site?
  • Do you have difficult ground conditions or any trees in close proximity to where you’re planning to build the extension?
  • Where does the water level in the ground naturally sit? Will the area need constant pumping to prevent flooding?

A basement or garage conversion can be a great way to add extra living space to your home if your options for a rear/side/loft extension are limited or if you don’t want to drastically change the exterior appearance of your home.

Interior Fit-Out Cost
Fit-Out costs can vary greatly depending of the function of the room (mainly affected by the cost of appliances) and are in addition to the above build costs.

  • Kitchen
    Budget from £7,000 to £15,000 – the biggest cost factor is the appliances – the better the appliances, the higher the cost
  • Bathroom
    Budget around £5,000 assuming you can connect to existing pipework
  • Utility Room
    Budget from £1,500 to £11,000 depending on size and quality of appliances
  • Underfloor Heating
    Budget from £10,000 to £15,000

Additional Costs:

  • Professional Fees (builders, architects, tradesmen)
    A new building of 20 square metres at a build cost of £30,000 could potentially attract professional fees from £12,000
  • Building Regulations Approval (All extension work requires building regulations approval and you may need building regulations approval for many alteration projects. However, you do not need to get approval yourself if you use someone registered with a competent person scheme) Budget from £400 – £750 if required.
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Do I need planning permission for a basement/garage conversion?
Converting an existing basement/garage into a usable living space does not require planning permission. This will be covered by permitted development (unless your home is in a conservation area or is a listed building). Permitted development costs £103.

Reducing the floor level of an existing basement or excavating a new basement are treated as an extension so may require planning permission. Planning permission costs £206.

Do I need insurance for a basement/garage conversion?
If you are carrying out conversion/extension works you should arrange specialist insurance to cover the new works and the existing structure as most home insurers won’t cover works if contracts exceed £50,000.

It is important to sort insurance in good time as most insurers will not insure when works have already started. GPS Insurance Brokers can provide specialist insurance cover for conversion/extension works and the insurance will last for the duration of the building project. Insurance should be arranged as soon as you know works will commence.

You should also inform your home insurer as an extra room could result in a higher buildings insurance premium. Failing to inform your insurer of any changes to your property could invalidate your home insurance policy.

For expert advise on this and any other insurance exposures, please contact Gary Philip at GPS Insurance Brokers on 020 8207 7385. GPS Insurance

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Total Cost
To calculate the cost of your project, Yoop Architects take a measured survey of your property, which captures all the information. Then we draw it all up in 3D and create sketches to show sometimes five or six options if it’s not entirely clear how you want to achieve your brief.

A lot of the times there are different ways of achieving your desired result and the more you work with the building, the cheaper, easier and faster your build will be. Once you’ve got a favorite scheme or a couple of favorite schemes, we have a phase called ‘Meet the Builders’. That’s when we can introduce you to a couple of builders, they visit the property and they give you a ballpark figure.


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