Outbuilding attached to house - planning permission

[reren]

My understanding of the permitted development rules is that an outbuilding /garage etc falls within permitted development if below 2.5 m height. I live on a corner plot and want to build a small storage building to the side of th house - it would not be visible to the street as it would sit behind an existing brick wall (and be shorter than 2.5m). I'm sure if it were detached permission wouldnt be needed but I wonder if it is needed if I create a door opening through the side of the house so we can walk through from house into the storage space? It wouldn't have any drains etc - but would want to put in lighting. I'm not sure when an outbuilding becomes an extension? I assume I would need building regs for it - but obviously that's a separate matter.

Anyone a wiz on understanding southward planning rules? I had a bad experience with the worlds rudest planner in the past and I had bad advice when I went to the one stop shop...so slightly wary of even raising it w planning office if I dont need to?

[The Minkey]

Technically a single story extension can be constructed without planning permission up to 15% of the volume of the existing building providing it hasn't been extended since 1947.

[m-architect]

Reren

The Planning Portal website does have a useful guide on permitted developments http://www.planningportal.gov.uk/permission/commonprojects/outbuildings/miniguide

From what you have described it seems as if it would fall under the 'permitted development criteria'. I hope this helps