Residential annexes
Commonly referred to as granny flats or ADUs, residential annexes are small, self-contained homes built on the same plot as an existing property. They give residents the opportunity to build a small additional home that enables families to support young adults or elderly relatives, or simply rented out to long-term tenants.
Already 12 local authorities in England allow residents to build residential annexes. These take multiple forms: side extensions or stand alone buildings.
The benefits of unlocking residential annexes
Homeowners often add an annexe to meet family needs, perhaps a space for a grandparent who needs support or for adult children.
Residential annexes can help ease the housing crisis, particularly in suburban areas. Millions of homes sit on plots that are sufficiently large to host an annexe. If we allow people to build annexes, we would help to increase supply of smaller homes in highly-constrained areas. Because annexes are small, they have no harmful visual impacts on the local area – most neighbours will never see them.
By allowing residential annexes, Britain could sustainably build infill homes – particularly in high-cost, low-density areas.
- Residential annexes would offer smaller, lower cost housing options in the suburbs of high-wage cities where workers want to live.
- Granny flats would support lifestyle changes within families.
- Annexes would boost SME builders by demand across a broad number of small sites.
- By boosting the density of suburbs that have existing, well-connected public transport infrastructure, new annexes can reduce the demand for car dependent housing development.
Learning from Los Angeles
In 2016, the state of California passed legislation to empower residents to build a residential annexe. The result has been notable, with over 100,000 annexe homes approved since.
Source: California ADU Reform: A Retrospective, California YIMBY
Building more homes through planning reform
The powerful impact of California’s reforms are clear: every one in three new homes approved in LA is an annexe. Just take a look at this map to see the progress.
Encouragingly, in California, the areas with the most annexe approvals are often in unaffordable suburbs like Palo Alto. When homeowners were given a clear route to build, they used it, increasing supply where it has been historically constrained. This demonstrates that ADUs can help build more homes where they’re needed most: in urban areas.
The rising tide of residential annexes
The phenomenon of residential annexe policy is not unique to California: similar policy reforms have taken place in Canada, Sweden, the Netherlands and Belgium, with Germany soon to follow suit.
Britain should learn from this increasingly common international practice, by reforming planning rules to enable popular annexes where they’re needed most.
Making it easier to build residential annexes in Britain
There are currently twelve Local Authorities with active planning policies that support homeowners to build an annexe. These policies tend to be in force in rural areas with large gardens and minimal new homes being built:
- Amongst national parks the Peak District actively ‘supports residential annexes in principle’, while Dartmoor lets farms add a detached rural-worker annexe of up to 40 m² GIA.
- In the South West, Cornwall defines garden annexes as ‘often acceptable’ (usually kept below 50% of the host footprint), South Gloucestershire’s SPD outlines a step-by-step checklist, and North Somerset promises permission inside settlement limits.
- East Anglia goes further: East Suffolk’s Rural-Development SPD, Babergh-Mid Suffolk’s policy LP02 and West Suffolk’s LP29 all state that compliant annexes ‘will be supported/permitted’.
- Finally, Havant (Draft Policy 35), King’s Lynn & West Norfolk (DM7), East Herts (HOU 13) and North Northamptonshire (2021 SPD) promise the same green light – so long as the unit and remains part of the household and shares the main access/utilities.
With these local authorities leading the way on residential annexes, Britain could emulate California’s state-wide system to unlock the new homes we need.
Support for residential annexes
There is growing support for policy reforms that make it easier for homeowners to build a residential annexe.
