Most new buildings or major changes to existing buildings or to the local environment need consent – known as planning permission. Without a planning system everyone could construct buildings or use land in any way they wanted, no matter what effect this would have on other people who live and work in their area.
Your local planning authority is responsible for deciding whether a development – anything from an extension on a house to a new shopping centre – should go ahead.
For further information on planning please follow this link http://wales.gov.uk/topics/planning/buildingregs/?lang=en.