The short answer
Usually yes, and often on more than one count. Because a side extension runs along the boundary, the foundations sit close to the neighbour (section 6), the new flank wall may be built on or up to the boundary line (section 1), and tying into or cutting into an existing party wall is party structure work — a party structure notice under section 3. A side-return, filling the side alley of a terrace, is the most common form, but the same applies to side extensions on semi-detached and detached houses where the work is close to the boundary.
Why it matters
Everything happens at the boundary, so the notices tend to combine:
- Building on the boundary (section 1) — a new wall on or astride the line. One month’s notice.
- Foundations (section 6) — footings alongside the neighbour’s wall. One month’s notice.
- Party wall works (section 2; party structure notice under section 3) — tying the new roof and wall into the existing party wall, and cutting in flashings. Two months’ notice.
Because the work is so close to the neighbour, access and protection (section 8) and a thorough schedule of condition matter a great deal. On a semi-detached or detached house you may be building right up to the boundary even where there is no existing party wall.
What to do now
- Check whether the new wall is on, or up to, the boundary, and get the foundation depths.
- Apply the section 6 tests and identify any party wall ties or cuts.
- Serve the right combination of notices, and plan access and protection early.
- If a surveyor is needed, use one. Both owners can appoint a single impartial ‘agreed surveyor’ rather than one each — quicker, cheaper and less adversarial. Coburns recommends a single agreed surveyor wherever possible.
Common mistakes
- Assuming a narrow infill is not notifiable.
- Building on the boundary without a line of junction notice.
- Missing the party structure works.
- Skimping on the schedule of condition when working this close.
When to call Coburns
Send us your plans and we will work out exactly which notices your side extension needs — line of junction, excavation and party structure — and serve them free of charge.