Airspace Above Your Building: Who Owns It, What You Can Build and Whether to Sell

Who owns the airspace above a building

Start with the title and the leases, not the roof. Ownership decides who can sell and who can object.

1. Freehold building, no long leases. The airspace is normally part of your freehold. You can develop it, sell it or lease it.
2. Building with long leasehold flats. Read the leases. Some include the roof or roof space in the top-floor flats. Most reserve it to the freeholder, but covenants on quiet enjoyment and access still apply.
3. Right of first refusal. Where a building contains flats, selling the airspace can trigger the leaseholders' right of first refusal. This comes from the Landlord and Tenant Act 1987. Get it checked before you market anything.
4. Commercial buildings. Check the leases for rights over the roof, such as plant, masts or signage. Check the landlord's right to build above too.

Two planning routes to new homes on a roof

There are two ways to get consent for new homes on top of a building. The building's age and location decide which one you can use.

Permitted development and prior approval

Since August 2020, Part 20 of the permitted development rules has allowed new homes on top of some existing buildings. You do not need a full planning application. The council only checks set matters through prior approval.

The main conditions are strict:

• The building was built between 1 July 1948 and 5 March 2018. Much of central London's Georgian and Victorian stock is older.
• It is not in a conservation area and not listed. That rules out large parts of inner London.
• One or two extra storeys, depending on the class and the existing height.
• The new homes meet the national space standards.
• The council approves external appearance, neighbours' light and privacy, natural light, transport, flooding and protected views.

For a 1960s or 1970s block outside a conservation area, this route can be faster and more certain. For a period terrace in Belgravia, it is usually not available.

Full planning permission

Everything else needs a full planning application. It is judged against the London Plan and your borough's policies on height, design, heritage and housing. In central London this is the normal route.

Rooflines, mansards and set-backs are judged street by street. A pre-application enquiry is often worth it before you commit. Our airspace and upward extension service handles both routes.

Whether the building can take more floors

Planning is half the answer. The other half is physical, and it is where builders earn their place.

1. Structure. New storeys add load to every floor, wall and foundation below. Many buildings have spare capacity, often only for light steel or timber frames. A structural survey and some opening-up give the real answer.
2. Fire and building safety. Extra floors change the fire strategy for the whole building. At 18 metres or seven storeys with two or more homes, it becomes a higher-risk building. Then the Building Safety Regulator approves the work before it starts.
3. Second staircase. Residential buildings with a storey at 18 metres or more must be checked against the second-staircase guidance early. It can decide whether a scheme works at all.
4. Sound and services. The new homes need sound separation from below. They also need their own water, drainage, power and ventilation.
5. Access and logistics. Cranes, scaffold, deliveries and working hours must be planned around residents or tenants.

Logistics is where rooftop schemes go over budget. At Portsoken House in Aldgate, our team delivered a £2.2M, 1,550 m² office conversion in seven months. The rest of the building stayed let. We worked nights and weekends so tenants were not disturbed. Building above an occupied building takes the same discipline.

The neighbours have rights too

Two legal regimes sit alongside planning. Both can stop or delay a scheme that already has consent.

1. Party walls. Raising or building on a party wall needs notices to the neighbours under the Party Wall etc. Act 1996. Most terrace schemes do this.
2. Rights of light. A neighbour who has had light through a window for 20 years may have a legal right to it. It can be enforced even after planning permission. A rights of light survey belongs in the feasibility stage.

Sell the airspace, develop it or partner

Once you know what can be built, there are three ways to turn it into value.

Selling with consent usually beats selling without it. The buyer is no longer paying for planning risk.

For freeholders of residential blocks, an airspace deal can also pay for a new roof, a lift or facade repairs. That can turn leaseholders from objectors into supporters. Craftex can co-invest, take 100% of the risk, or work on a fee or percentage basis, depending on the stage.

Weighing the routes for land rather than a roof? Read option vs promotion agreement vs joint venture.

How our team assesses airspace

We look at airspace as planners and builders at once. A first visit checks the title position, the planning route, the designations and the obvious structural questions.

If it is worth going further, a feasibility study tests the structure. It designs the options and prices them with our own construction team. Our Preconstruction Director, Martin Hickey, brings more than 50 years in construction to every appraisal.

To see what consent would add to your building, read about land value uplift. We take development schemes from £3M to £150M GDV.

Ready to find out what sits above your roof? Book a site visit and we will walk you through each check on site.