Extension.

[Cassimin]

We have a double extension on the side of our house. We are a semi detached.
Next door ( it’s my son) wants to build a double extension. Are they allowed to build and use our side wall, leaving no gap?

Is your wall on the property line or 2cm inside the property line?

they might need a party wall agreement & should probably have advice from a surveyor

I think it may be on the property line.

We had the extension built and we’ve since had insulation on it.
The pipe from our boiler sticks out too so we are probably on his property with this.
That may be a problem as this will need re routing

I imagine you'd need planning permission as the council usually have a street view set of rules about how a street should look and if people are allowed to infill between properties.