London Assembly calls for rooftop-extension pattern book to unlock housing
The Greater London Authority (GLA) should create a pattern book for upward extensions to boost housing supply, the London Assembly Planning and Regeneration Committee has said
In a letter to London mayor Sadiq Khan, the committee cited estimates that between 140,000 and half a million new homes could be built on top of existing residences within current planning regulations. Uncertainty and risk are blamed for holding developers back.
The letter recommends the GLA creates a pattern book to define acceptable design for upwards extensions, which local authorities could either apply or adapt.
The call is a response to the publication of the draft London Plan in July, which encouraged the development of ‘strategies, design guides, design codes and/or masterplans’ for ‘areas where a more pro-active approach is required to promote development’.
The committee says such a code would function in the same way as the Small Sites Design Code, released for consultation earlier this month, which the committee says provides ‘an opportunity to establish a more consistent approach to support well-designed intensification’.
The letter’s author, Labour assembly member James Small-Edwards, said: ‘London’s housing crisis is the single greatest challenge our city faces today. At its root, this is a crisis born out of a need for more high-quality homes, particularly social and affordable homes. Upwards extensions could form part of that longer-term strategy.
‘The committee encourages the GLA to use the next 10 years to reduce barriers to delivery by providing greater policy certainty and supporting standardised approaches where appropriate and locally supported, so that upwards extensions can make a more meaningful contribution to London’s housing supply in the decades ahead.’
Small-Edwards added that pattern books and design codes could provide a ‘clear framework’ for the delivery of housing densification in schemes such as upwards extensions, while ‘respecting the distinctive qualities of London’s historic neighbourhoods’.
Past efforts to promote upwards extensions have focused on lifting planning restrictions, with permitted development rights introduced in 2020 allowing most building types to be built up by two storeys, subject to prior approval.
Further changes to these rules, which would have altered the requirement for buildings to have been constructed after 1948 to benefit from permitted development rights, went to consultation in 2024, but are still under consideration according to the latest government update.
Both the National Planning Policy Framework (NPPF) and the most recent edition of the London Plan include specific calls to support the use of airspace above residential and commercial properties for the development of new homes.
Reacting to the letter, Ben Clark, director at 2C Architects, told the AJ: ‘One of the things that makes London great is its historic building stock, but those buildings have never really stood still. They’ve always changed and adapted over time as the way we live, work and use buildings has changed.
‘For me, that adaptability is a big part of sustainability. The most sustainable buildings are often the ones that can keep evolving rather than becoming obsolete. We’ve been doing that in London for hundreds of years, so upward extensions are really part of that wider story of buildings changing with the city.’
Clark added that anything that might help to reduce unnecessary barriers to development ‘has to be a good thing’. He said design codes could be useful in ensuring that a more ‘relaxed planning environment’ doesn’t mean poorer design quality.
The Planning and Regeneration Committee noted that despite the policy momentum behind boosting housing supply, ‘delivery has been comparatively low’.
The letter puts this down to increased risk associated with new building regulations, especially post-Grenfell reforms, which have compounded the ‘technical and financial challenges’ of this kind of development.
It cited two borough-specific design codes, in Tower Hamlets and Haringey, that already provide a framework for upwards extensions. These efforts were said to have ‘created certainty for residents’ while allowing the areas to ‘preserve and maintain character’.
But Oliver Cooke and Francis Fawcett, directors at architecture practice Cooke Fawcett, warned that any framework needed to avoid the mistakes of previous changes to permitted development rules.
They said: ‘Permitted development is, in many ways, a design disaster. It opened up a route that too often ends with a dumb box plonked on top of someone’s home.
‘[The planning process for] roof additions has reached a surreal situation in which anything triggering full planning often meets significant resistance. [Yet], in parallel, all manner of poorly designed additions are sailing through via permitted development (PD).
‘Any new framework that feels like PD-on-steroids risks the same outcome unless design quality is genuinely built into the policy from the start.’
The mayor is expected to respond to the letter by 3 November.
Further comment
Greg Walton, director, Studio McW
There are absolutely parts of London where greater density and additional height would be appropriate, and reducing some of the barriers to upward extensions could create more opportunities to add homes and space without relying on demolition and rebuilding.
We tend to think of the housing stock as fixed, when London has always adapted and evolved. Houses have been extended, subdivided and reconfigured as patterns of living have changed. Perhaps the question should be how the homes we already have can become more adaptable, rather than simply how we build more homes.
Post-war social housing developments, for example, could be well suited to this approach. Often relatively low-density and flat-roofed, they could accommodate new homes within existing communities and infrastructure without overwhelming them. It’s an opportunity for incremental intensification.
The London Assembly is rightly focused on increasing housing supply, but another benefit is that adding space to existing homes can allow families to stay where they already live as their needs change. Rather than being a five-year house, a home can become a 15-year house, retaining its embodied carbon, location and connection to the local community.
The question of whether an addition is appropriate to a particular building, street and neighbourhood remains crucial, rather than simply whether we can add extra storeys.
There is a real opportunity to make better use of what London already has. Loosening restrictions could allow more buildings to evolve, whether that means adding new homes, extending the life of existing homes or making better use of small, well-connected sites. But this shouldn’t be seen as a case for simply building higher everywhere. Additional height should always respond to the building, street and neighbourhood.
Oliver Cooke and Francis Fawcett, directors, Cooke Fawcett
We are often doing enormous amounts of work to obtain consent for additions which in a lot of contexts should really be a given – adding an extra floor to a two-storey house in contexts where there is little or no heritage constraint, for example.
Some form of zoning or pattern book approach could be transformative, giving homeowners a much clearer understanding of what is possible when they buy a property, and letting architects focus their energy on design quality rather than justifying the principle.
In a way, this could be like the recent draft policies for small sites developments in London, which seem very helpful in defining what should be accepted in varying circumstances.
Once you start thinking seriously about the energy and amenity implications of building higher, you quickly find yourself in questions about how roof space is used – M&E plant, outdoor space, ventilation. There is still a strong planning bias against these elements in a domestic context, with officers seeing them as ‘visual clutter’ rather than as the necessary reality of modern climate-resilient construction. This feels contradictory if the policy ambition is genuinely to embrace adding floors to existing buildings.
That shift in design approach needs to be part of the conversation.
In our experience, people who own and live in existing flats rarely welcome the idea of someone building above them. There is very little in it for existing residents beyond disruption and uncertainty – and that dynamic alone represents a significant barrier to delivery at scale, regardless of what planning policy says.
The Greater London Authority (GLA) should create a pattern book for upward extensions to boost housing supply, the London Assembly Planning and Regeneration Committee has said
In a letter to London mayor Sadiq Khan, the committee cited estimates that between 140,000 and half a million new homes could be built on top of existing residences within current planning regulations. Uncertainty and risk are blamed for holding developers back.
The letter recommends the GLA creates a pattern book to define acceptable design for upwards extensions, which local authorities could either apply or adapt.
The call is a response to the publication of the draft London Plan in July, which encouraged the development of ‘strategies, design guides, design codes and/or masterplans’ for ‘areas where a more pro-active approach is required to promote development’.
The committee says such a code would function in the same way as the Small Sites Design Code, released for consultation earlier this month, which the committee says provides ‘an opportunity to establish a more consistent approach to support well-designed intensification’.
The letter’s author, Labour assembly member James Small-Edwards, said: ‘London’s housing crisis is the single greatest challenge our city faces today. At its root, this is a crisis born out of a need for more high-quality homes, particularly social and affordable homes. Upwards extensions could form part of that longer-term strategy.
‘The committee encourages the GLA to use the next 10 years to reduce barriers to delivery by providing greater policy certainty and supporting standardised approaches where appropriate and locally supported, so that upwards extensions can make a more meaningful contribution to London’s housing supply in the decades ahead.’
Small-Edwards added that pattern books and design codes could provide a ‘clear framework’ for the delivery of housing densification in schemes such as upwards extensions, while ‘respecting the distinctive qualities of London’s historic neighbourhoods’.
Past efforts to promote upwards extensions have focused on lifting planning restrictions, with permitted development rights introduced in 2020 allowing most building types to be built up by two storeys, subject to prior approval.
Further changes to these rules, which would have altered the requirement for buildings to have been constructed after 1948 to benefit from permitted development rights, went to consultation in 2024, but are still under consideration according to the latest government update.
Both the National Planning Policy Framework (NPPF) and the most recent edition of the London Plan include specific calls to support the use of airspace above residential and commercial properties for the development of new homes.
Reacting to the letter, Ben Clark, director at 2C Architects, told the AJ: ‘One of the things that makes London great is its historic building stock, but those buildings have never really stood still. They’ve always changed and adapted over time as the way we live, work and use buildings has changed.
‘For me, that adaptability is a big part of sustainability. The most sustainable buildings are often the ones that can keep evolving rather than becoming obsolete. We’ve been doing that in London for hundreds of years, so upward extensions are really part of that wider story of buildings changing with the city.’
Clark added that anything that might help to reduce unnecessary barriers to development ‘has to be a good thing’. He said design codes could be useful in ensuring that a more ‘relaxed planning environment’ doesn’t mean poorer design quality.
The Planning and Regeneration Committee noted that despite the policy momentum behind boosting housing supply, ‘delivery has been comparatively low’.
The letter puts this down to increased risk associated with new building regulations, especially post-Grenfell reforms, which have compounded the ‘technical and financial challenges’ of this kind of development.
It cited two borough-specific design codes, in Tower Hamlets and Haringey, that already provide a framework for upwards extensions. These efforts were said to have ‘created certainty for residents’ while allowing the areas to ‘preserve and maintain character’.
But Oliver Cooke and Francis Fawcett, directors at architecture practice Cooke Fawcett, warned that any framework needed to avoid the mistakes of previous changes to permitted development rules.
They said: ‘Permitted development is, in many ways, a design disaster. It opened up a route that too often ends with a dumb box plonked on top of someone’s home.
‘[The planning process for] roof additions has reached a surreal situation in which anything triggering full planning often meets significant resistance. [Yet], in parallel, all manner of poorly designed additions are sailing through via permitted development (PD).
‘Any new framework that feels like PD-on-steroids risks the same outcome unless design quality is genuinely built into the policy from the start.’
The mayor is expected to respond to the letter by 3 November.
Further comment
Greg Walton, director, Studio McW
There are absolutely parts of London where greater density and additional height would be appropriate, and reducing some of the barriers to upward extensions could create more opportunities to add homes and space without relying on demolition and rebuilding.
We tend to think of the housing stock as fixed, when London has always adapted and evolved. Houses have been extended, subdivided and reconfigured as patterns of living have changed. Perhaps the question should be how the homes we already have can become more adaptable, rather than simply how we build more homes.
Post-war social housing developments, for example, could be well suited to this approach. Often relatively low-density and flat-roofed, they could accommodate new homes within existing communities and infrastructure without overwhelming them. It’s an opportunity for incremental intensification.
The London Assembly is rightly focused on increasing housing supply, but another benefit is that adding space to existing homes can allow families to stay where they already live as their needs change. Rather than being a five-year house, a home can become a 15-year house, retaining its embodied carbon, location and connection to the local community.
The question of whether an addition is appropriate to a particular building, street and neighbourhood remains crucial, rather than simply whether we can add extra storeys.
There is a real opportunity to make better use of what London already has. Loosening restrictions could allow more buildings to evolve, whether that means adding new homes, extending the life of existing homes or making better use of small, well-connected sites. But this shouldn’t be seen as a case for simply building higher everywhere. Additional height should always respond to the building, street and neighbourhood.
Oliver Cooke and Francis Fawcett, directors, Cooke Fawcett
We are often doing enormous amounts of work to obtain consent for additions which in a lot of contexts should really be a given – adding an extra floor to a two-storey house in contexts where there is little or no heritage constraint, for example.
Some form of zoning or pattern book approach could be transformative, giving homeowners a much clearer understanding of what is possible when they buy a property, and letting architects focus their energy on design quality rather than justifying the principle.
In a way, this could be like the recent draft policies for small sites developments in London, which seem very helpful in defining what should be accepted in varying circumstances.
Once you start thinking seriously about the energy and amenity implications of building higher, you quickly find yourself in questions about how roof space is used – M&E plant, outdoor space, ventilation. There is still a strong planning bias against these elements in a domestic context, with officers seeing them as ‘visual clutter’ rather than as the necessary reality of modern climate-resilient construction. This feels contradictory if the policy ambition is genuinely to embrace adding floors to existing buildings.
That shift in design approach needs to be part of the conversation.
In our experience, people who own and live in existing flats rarely welcome the idea of someone building above them. There is very little in it for existing residents beyond disruption and uncertainty – and that dynamic alone represents a significant barrier to delivery at scale, regardless of what planning policy says.
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