Nauman Zafar | Party Wall Consultant | Survey of Party Wall · Last Updated: June 2026 · Reviewed against the Party Wall etc. Act 1996 and Pyramus & Thisbe Club best practice
What Counts as the Party Wall on a Semi
Common semi detached projects that trigger the Act: rear extensions tied into the shared wall, loft conversions with steels bearing on it, chimney breast removals on the shared stack, and any basement or foundation work within 3 metres of next door.
Typical Costs for a Semi in 2026
| Project | Agreed Surveyor | Separate Surveyors |
|---|---|---|
| Chimney breast or beam insertion | £900 to £1,400 | £1,600 to £2,200 |
| Rear extension | £1,350 to £2,000 | £2,000 to £3,000 |
| Loft conversion | £900 to £1,800 | £1,800 to £3,200 |
| Basement | £4,500 to £7,500 | £6,600 to £11,500 |
Full breakdown in our party wall surveyor fees London guide. The building owner pays all reasonable fees under Section 10(13).
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Three Scenarios
Representative illustrative scenarios. Not named clients.
Scenario 1. A Finchley semi owner planned a rear extension and loft together. One combined notice package, one agreed surveyor, one award covering both. Saved roughly £1,200 against running two separate processes.
Scenario 2. A Streatham semi owner removed a chimney breast on the shared stack without a notice, believing internal work was exempt. The neighbour noticed debris in their flue. A retrospective process and remedial works cost over £3,000.
Scenario 3. A Sutton semi owner served notice for a rear extension. The neighbour, anxious about a newly decorated kitchen, dissented and appointed their own surveyor. The award added vibration limits and the schedule of condition recorded the kitchen in detail. Works completed without dispute.
Key Takeaways
- The dividing wall on a semi is a party wall, the rear garden wall may be a party fence wall
- Section 2 needs two months notice, Sections 1 and 6 need one month
- One neighbour means one conversation, the agreed surveyor route is usually best on a semi
- Internal works like chimney breast removal still trigger the Act when they affect the shared wall
- Building owner pays all reasonable fees under Section 10(13)
Frequently Asked Questions
Does the Party Wall Act apply to my semi detached house?
Yes, whenever works affect the shared dividing wall, build at the boundary, or excavate within 3 metres of next door below their foundations.
Do I need a notice for a chimney breast removal in a semi?
Yes if the breast is on the shared stack or wall. It is Section 2 work with a two month notice period.
What if my semi neighbour ignores the notice?
Silence for 14 days is deemed dissent under Section 10. A surveyor is then appointed and an award produced. The works proceed under the award.