Rear extension of a semi-detached house

[yogi22kar]

My neighbour with whom I have a common wall of our semi-detached house wants to extend his property at the rear end.
I too wish to do a rear extension, but not immediately.
My neighbour is quite keen that we apply for a planning permission for rear extension at the same time for following benefits:
1. The common wall that needs to be extended will be of smaller thickness. In fact he claims that we will be able to save about 9 inches individually, as this wall will be treated as an internal wall, instead of an external wall.
2. It will be easier and quicker to get planning permission from council

Can anyone please confirm the claim about saving the space due to wall thinness?
Thanks in advance.

[Perry525]

If you go up into the loft, you will probably see that the double brick/block thickness of the wall, decreases to one brick. This is normal with terraced houses.
If you both build identical extensions at different times, you will end up with a massive wall between the homes.
This may not be a bad thing, as mass is a good absorber of noise and the two rooms will be quieter. You will each lose the equivalent of one brick thickness in your room.
You will of course have to pay for the extra blocks and mortar and the builders time, delivery etc.

[DevilDamo]

Is this is a single or two-storey extension?

If it's a two-storey, the "main" advantages of going in for planning approval for a pair of semi-detached houses is that you can extend more than you would normally be allowed to taking into account neighbouring windows to habitable rooms.

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