Already have an extension..... do I need planning permission for loft conversion

[Alice Lou]

Hi I really need some advice

We live in an end terrace the previous owners put on a two storey extension to the side of the property with planning permission. I would say it's not quite doubled the size of the property but nearly.

We have had a number of people come to look at doing a loft conversion. Two companies have given opposing advice. One company said if we put a small dormer at the back and make a bedroom out of the original floor space of the house (the extension has a slopping roof so wouldn't give head head for a room without redoing the roof) no planning permission is needed but another company said we will because the additional living space we create in the loft added to the extra living space the extension created will be over the threshold allowed.
What are people's thoughts on this? I don't want to go with the company who said we don't need it and then end up with problems but don't want to go through planning if I don't need to as we are working on a time scale as have a baby due in Sept

Thank you

 

[tony1851]

If the roof of your extension is physically joined to the original house roof, then your starting point is the total increase in roof volume. If the volume of the roof over the extension, plus the volume of your proposed dormer, would be more than 40m³, then you would need planning permission.
In any event, if your proposed dormer encroached into the roof volume of the extension, that would also need p.p.
The only way you would avoid planning permission is if you kept the dormer only over the original house (and kept it below 40m³).