In short
What is particular to rebuilding one half of a semi-detached pair: the plot and storey rules, keeping or leaving the party wall, what you owe the house next door, and whether a semi-detached plot can become a detached house.
Your half, and the half next door
A semi-detached house is one half of a pair, each half on its own title, joined by a party wall. You can rebuild your half on its own: if you do, your neighbour's half stays a semi-detached house as approved, and the same is true for you if they rebuild first.
URA's minimum plot is 200 square metres, 8 metres wide for a side-to-side pair or 10 metres for back to back. Height comes from the storey control for your area on the Landed Housing Area Plan, within the envelope control every landed house now follows. These are URA's published guidelines as they stand; URA can depart from them case by case, so your qualified person confirms what applies to your plot before anything is drawn.
The party wall decides the approach
URA generally does not allow a new blank party wall on the boundary. That leaves two approaches:
- Keep part of the existing party wall within your plot, and build your new house against it.
- Build clear of it, which leaves your neighbour's wall exposed. You then owe them an engineer's certificate to BCA on the stability of their house, plaster and paint on the exposed wall and a neat roof edge once demolition is done, and access for them to maintain it.
Neither is better in every case. The choice depends on the condition of the shared wall, the plan you want, and how your neighbour's house is built, and it is made at feasibility, before design starts.
Working alongside the house next door
A pre-construction survey of the neighbouring house is required before demolition, piling or excavation. It protects both of you: any crack that appears later is compared against a dated, photographed record instead of a memory.
Tell your neighbour in writing, before the hoarding goes up, what is happening and for how long, and ask for consent where works need access to their side. Most party-wall disputes start with a surprise rather than a disagreement.
Detached from a semi-detached plot
Owners sometimes ask whether a semi-detached plot can become a detached house. It can only where the plot meets the bungalow minimum of 400 square metres and 10 metres wide and the area permits detached houses. Changing the housing form counts as reconstruction whatever the floor-area change, so it goes through the full approval route.
Designing the new half
Because the new half follows today's envelope and setbacks, it is often taller or deeper than the house beside it. The design work is making the pair sit well together anyway: a roofline that steps rather than jumps, materials that relate to the older half, and a frontage that reads as one house on a shared street rather than two that disagree.
For the decision before this one, see Rebuild or A&A?; for what to check on a plot you have not bought yet, Buying a plot: what to check.
Key takeaways
- URA's minimum for a semi-detached house is 200 sqm, 8 m wide side to side or 10 m back to back.
- Your half can be rebuilt on its own; the other half remains a semi-detached house as approved.
- Leaving your neighbour's wall exposed brings an engineer's certificate, making good, and access for them.
- Turning a semi-detached plot into a detached house needs the plot to meet the bungalow minimum.
Questions people ask
Not to rebuild on your own plot, but you need their written consent to enter their property for works on the party wall, and they should be told before works begin. If access is refused, the method can often be changed to avoid it.
