Southwark Council, in partnership with Wikihouse Foundation and Future Cities Catapult, are developing a user-friendly app that allows household extension applicants to play around with the massing and layouts of their proposal and receive an automatic green-amber-red indication of the likelihood it will be compliant with building control codes and planning policy. The council has developed detailed rules on how amenity impacts and building control requirements are assessed within the app, with the rollout likely to make small applications more efficient and cut much of the long tail of small planning queries that take up case officers’ time.