Do I need Planning permission?

In most cases, No. 

Back in 1948 the government introduced something called permitted development. In 2015 this sheme was revised, updated and broadened. 

This  scheme sets out specific rules and  parameters that allows home owners to make changes and additions to a property and garden. without having to apply for planning permission. 

Section E of the government guidelines sets out the rules for outbuildings on your property.  

These include:

• Dimensions 
• Height limits
• Distances from boundaries
• Limits of use.

Let's talk about the 50% rule. 

Your building must account for less than 50% of the land around your house. 

  So for example. If you have 100sqM of land. (not including your house) your building must be less than 50sqM.

However, if you have already extended or have other outbuildings these will eat into your 50%.  For example, if you have a 2mx2m shed and a 3m x 2m  extension , that's 4sqM and 6sqM, 10sqM total that you'd have to take off your 50sqm. Leaving you with 40sqm left for a building  within Permitted development. 

What about the Height? .  

This can get a little confusing too 

because the height limits of an outbuilding within Permitted development depends on other factors.

  The main limiting factor here is it's distance from your boundary or house. 

If your building has a dual pitched roof (Imagine a traditional triangle type roof with a ridge) it can be 4 metres high at the ridge.  If its a single pitch roof it can only be 3 metres at the highest point, and a maximum of 2.5 metres at the lowest point. 

However if your building is within 2 metres of a boundary or your house, then the maximum height of the building at ANY point is 2.5metres. This height is measured from the ground at its highest point adjacent to the new building.