Build new walls for extension or rebuild old?

[diy_darren]

Below is my attempt at an ascii plan! Scale is not quite right, but layout is ok.

I'd like to build an extension (not joining existing building) in the top right corner of my garden, but I'm unsure whether to come inside my existing boundary fences (all 2m high) and build a double skin wall, or rebuild the boundary fences on 1m foundations first.

If I come inside the current boundaries, how much gap would I leave? The top fence is wood panel, but the right hand side is a single brick wall that overlaps sections every 3m. It has little foundations and I wouldn't want to collapse it while digging in foundations for the new building. This seems a simpler solution although I would lose a slight bit more garden area.

If I rebuild the boundaries I would take down the right hand wall, put in 1m foundations and rebuild it. Part of it needs rebuilding anyway as a tree has pushed it out (right above garage). I'd have to join it to the existing wall that the garage uses as I don't have the money to demolish the lot and rebuild the garage too. The top fence is wood panelling so I'd remove part of it and replace with the double skin wall of the new building, not a huge issue.

Any thoughts?

[code:1]
|--------------------------------|
| |
| |
| |
| |
| \
| O/
| --------|
| | Gar. |
| ------------------| |
| | Conservatory | |
| ------------------| |
| | | |
| | | |
| | |-------|
| | | |
| | House | |
| | | |
| | | |
| | | |
| |-----------------| |
| |
| |
|--------------------------------|
[/code:1]

 

[iangh]

What you propose is a separate hereditament, you will be Council taxed on it for sure, if planners allow.
In my area they would call it 'tandem development ' and chuck it in the bin.
all assuming it is not a shed that you are needing

 

[diy_darren]

The building will only be connected to mains electricity and not able to function as a separate unit. I am in the process of a planning application at the moment, so I keep my fingers crossed

The problem is that the new room is to house a pool table and must have a width of 5m. The existing garage is only 4m and joining it would create a 1m overlap with the conversatory making it damn aweful in my opinion. It would also hide a large section of the garden behind it.

I hope I can persuade the planning officers otherwise I'll put forward a poly tunnel connection to the existing garage