Planning permission is always required unless the proposal is 'permitted development'.
Information and guidance on permitted development can be found on What is permitted development? or the Planning Portal (this page opens in a new window). The Planning Portal includes an interactive house to guide you through what needs planning permission for residential properties.
If your development does not come under 'permitted development' then you will need to apply for planning permission. Further advice can be found on Can I get advice before I submit my application? and Advice on making an application.
Planning Services
Guildford Borough Council
Millmead House
Millmead
Guildford
GU2 4BB
Tel: 01483 444609
Email: planningenquiries@guildford.gov.uk