Hi
The main issue you will have to deal with with a single skin wall is rainwater penetration after you have that problem resolved you can start looking at how to insulate the room.
Second point - why don't you go for a conservatory - half the price and half the hassle!
Also you have permitted development which would allow you to build a single storey extension out 3metre's from the existing building line without the need for Planning Permission although you would still need to meet the requirements of the BR, again a conservatory would get over this issue.
Regards
The main issue you will have to deal with with a single skin wall is rainwater penetration after you have that problem resolved you can start looking at how to insulate the room.
Second point - why don't you go for a conservatory - half the price and half the hassle!
Also you have permitted development which would allow you to build a single storey extension out 3metre's from the existing building line without the need for Planning Permission although you would still need to meet the requirements of the BR, again a conservatory would get over this issue.
Regards