Flat Conversions

Each property varies substantially, so it very hard to put a price on it, that being said it can cost between £25k to £100,000 per flat dependant on many factors such as whether their extensions required, if there is a complete gut out with structural works required, fixtures and fitting can play a massive role as well. whether budget, mid-range, or premium, will substantially impact the final price tag.

As mentioned above Structural changes represent one of the largest potential expenses. Removing load-bearing walls, adding new staircases, or reinforcing floors can quickly escalate costs. Location significantly influences your budget, with London and the Southeast typically seeing prices 20-30% higher than other regions of the UK due to increased labor and material costs. The key is space planning, trying to do minimum number of structural alterations to achieve the same end result.

Electrical and plumbing modifications form a substantial portion of conversion expenses, especially when installing multiple new kitchens and bathrooms with separate service connections. Fire safety requirements cannot be overlooked, as regulations mandate fire doors, alarm systems, and proper compartmentation between units, all adding to your overall investment.

Local council often impose discharge of conditions for external landscaping, bin storage, cycle storage and now the urban green factor scoring when you do a flat conversion. External works often get underestimated in initial budgeting. Professional fees must also be factored in, including qualified chartered architectural technologist (typically 8-15% of the project cost), structural engineers  and planning applications are all additional fees that are required.

The next set of fees that will be likely to be incurred are local council fees for building regulations submission or an approved inspected fees which varies. With this you may need a party wall agreement which can cost £700 to £1500 per agreement plus the cost of the other side surveyor. Energy efficiency improvements to meet minimum EPC requirements can add £5,000-£15,000 to your budget, and new utility connections with separate meters typically cost £1,000-£3,000 per flat.

It is advisable to allow for contingency fee of  10-15% of your total budget to address unexpected issues that inevitably arise during conversion projects. Before going out to tender it is advisable to seek advice from a quantity surveyor who will be able to produce a detailed bill of quantities.

The starting point which we tend to use is the London Plan first and foremost. This gives you the general outline of what to be included in your design layout, most notably policy D6 states the minimum flat sizes, standards required for residential units. Studio flats for one person must have at least 37m² of Gross Internal Area (GIA), while one-bedroom flats require 39m² for single occupancy and 50m² for double occupancy. Two-bedroom flats need 61m² for three people or 70m² for four people. For larger families, three-bedroom flats must provide 74m² for four people, 86m² for five people, and 95m² for six people.

Beyond floor space, the London Plan states ceiling heights of at least 2.5m for a minimum of 75% of the GIA. Built-in storage space must also be provided, starting at 1.5m² for one-bedroom units and increasing incrementally with each additional bedroom, reaching 3.5m² for units with four or more bedrooms. Private outdoor space is another requirement, with a minimum of 5m² allocated for one to two-person dwellings, plus an additional square meter for each extra occupant.

Dual aspects are very important for Flat Conversion within any borough. Usually this leads to a rejection if they are not included; however, if you have a sunlight assessment to prove light is traveling to each habitable room, this can go in your favor.

If you plan a new build flat conversion, accessibility can play an important role in the flat conversion. Your council may impose that the flat conversion must meet M4(2) ‘accessible and adaptable’ standards.

Borough-Specific Planning Policies

As mentioned above, the London Plan is the go-to element. With that, each borough has their local planning policy which can be key for assessing the adequate communal space, additional things for example retention of a three-bedroom flat as the area needs it, there could be a restriction on studio flats, or the mix proposed. It is very important to look at each design guide. Article 4 directions may restrict permitted development rights in specific areas, limiting what can be done without full planning permission. Conservation areas impose additional restrictions on external alterations and aesthetic considerations to preserve local character.

For larger conversions, anything above 9 units, there will be an element of affordable housing contribution. Parking standards vary by borough, with specific requirements for both car and bicycle parking spaces, including accessibility provisions. Community Infrastructure Levy (CIL) and Section 106 agreements often entail financial contributions and obligations to support local infrastructure and services.

If you plan to build a basement as part of the flat conversion, you must look at your local planning policy as basements vary from council to council, some imposing strict requirements. A basement impact assessment and flood risk assessment may be required to prove the basement will not affect the local area or neighboring properties.

Application Requirements

A planning application for a flat conversion dependent on the size and scale, this will include detailed existing and proposed floor plans to demonstrate all space standards are met, a sectional drawing to demonstrate heights have been met, usually a design access statement will be required to demonstrate how planning policies and accessibility requirements. Daylight and sunlight assessments demonstrate the impact on light levels both within the proposed units and for neighbouring properties.

Noise impact assessments address potential acoustic issues, while heritage statements explain how the conversion respects the building’s historical significance if applicable. Energy statements demonstrate compliance with sustainability requirements, and a fire strategy outlines safety measures.

These are some of the documents that may be required again it is all dependant of the area your property is within.

Flat conversion typically require full planning permission because a change from a single dwelling to multiple flats is considered to be a material change of use even though it within the same use class. Local authorities need to ensure compliance with space standards, fire safety regulations, and assess impacts on parking and local services.

While the government has expanded permitted development rights for certain commercial-to-residential conversions (Class MA), these rights do not apply to houses to flat conversion, all local authorities maintain control over flat conversion through their local planning policies, to ensure quality standard and undue stress on their streets.

Some council have taken a steps to protect areas by applying an Article 4 directions specifically to remove permitted development rights for flat conversions in certain areas where there are concerns about housing mix and community balance. For any house-to-flats conversion, you will need to submit a full planning application that demonstrates compliance with both national and local planning policies, including the minimum space standards outlined in the London Plan if your property is in London.

However, it’s important to note that under existing regulations, converting a single house into two flats may be possible under permitted development rights in some circumstances, particularly through the Class G permitted development right.

This comes with significant restrictions and conditions, including that the building must have been used as a single dwellinghouse on 23 March 2023, both resultant dwellings must meet nationally described space standards, and prior approval from the local planning authority is still required.

If you have converted your property without formal planning or you have added an additional bedroom to your flat conversion plans without informing the council, you could be in breach leading to an enforcement, therefore you must do one of the following

1. Apply for a Certificate of Lawful Use existing: if you have converted your houses into flats for more than 4 years which has now been increased to 10 years you, you may be able to apply for a Certificate of Lawful Use, which effectively provides immunity from enforcement. For this type of application you must prove beyond reasonable doubt that the flat had been there for a period of 10 years, this can be done by sworn affidavit, tenancy agreement, council tax bills so on.
2. Restore the property: If planning permission is denied and no certificate can be obtained, you may be required to restore the property to its original condition.

Proceeding without resolving planning issues can lead to enforcement action, difficulties selling the property, and potentially significant financial penalties. Our team can provide guidance on navigating this complex situation and help you achieve compliance with minimal disruption.

A flat conversion project’s timeline varies depending on a number of factors:

• Phase of planning and design: two to four months (including application for planning permission)
• Approval of building regulations: one to two months
• Phase of construction: three to eight months, depending on the size and complexity of the property.
• Final certification and inspections: two to four weeks

From the initial concept to completion, a simple conversion of a moderately sized house into two apartments could take six to eight months. It could take 12 to 18 months for more intricate projects with several apartments or major structural alterations.