Agent Knight Frank produced a report late last year estimating 40,000 homes could be built on top of existing buildings in Central London alone.
The Mayor of London, Sadiq Khan, also gave his support to rooftop developments and the recently published NPPF guidelines made clear that planning authorities should support well designed and appropriately scaled schemes of this nature.
However, building on rooftops is not straightforward and requires considerations very specific to this type of development.
It is not the same as building on a cleared site. Instead, rooftop schemes should be seen as new build projects with their foundations many metres in the air and as the extension of an existing building.
Pellings is working with clients on such projects at various stages from initial viability to those where it is already procuring contractors.
Because of this experience it has created a 10-point plan for landlords to consider when deciding whether to embark on such schemes.
- Identifying key drivers: the condition of the existing building, looking at housing need, considering whether there are other airspace opportunities and being aware of S.106 obligations.
- Initial viability studies: undertake water, drainage, gas, and electricity surveys and existing capacity of lifts, parking, play and landscaping areas and tenure mix.
- Occupancy issues: consider leaseholder and tenancy positions including the need for statutory consultation, service charge issues, loss of amenity, and increased noise.
- Technical validation: include compliance with health and safety regulations, means of escape, sustainability studies and energy performance.
- Planning and statutory issues: including space standards, floor-to-ceiling heights and apartment orientation.
- System selection: consider the most appropriate construction method for the project whether it be -on or off-site construction.
- Contracts and procurement: consider design and build and contractor selection.
- Technical specifications: use NBS/NHBC and other guidance, avoid over innovation; ensure good mechanical and electrical integration by using BIM if possible.
- Guarantees: be clear on the guarantee requirements for the new units and engage early.
- Cost and risk: develop a full elemental cost plan and costed risk register with evaluated risk reduction/mitigation measures at all stages of the design and works procurement for the project.
By adopting the approach outlined above and adopting a structured framework for assessing the viability of a project, the prudent landlord will be able to identify the pitfalls as well as the benefits.
This minimises the risk of project failure and financial loss later on.