On a detached house you can hack a wall on a Tuesday and nobody else is involved. On a terrace or a semi-detached, the wall you want to touch may be holding up your neighbour's house as well as yours — and the conversation you have with them before the works start is worth more than anything you can put in a contract afterwards.

This is the part of an A&A job on an attached house that homeowners consistently underestimate. Not the design, not the cost. The boundary.

First establish what the wall actually is

People use "party wall" loosely to mean any wall on a boundary. In practice, on Singapore terrace and semi-detached houses, you will meet several different situations and they behave differently:

• A genuinely shared structural wall, carrying floors and roof on both sides. Common in older terrace rows. Anything you do to it is structurally your neighbour's business as well as yours.
• Two separate walls built hard up against each other, each carrying its own house. Common in newer developments. Your wall is yours — but there is no working space between them, and that changes what is buildable.
• A boundary wall that carries nothing, dividing the plots at the side or rear. Ownership may be shared, may be one owner's, and is frequently unclear.
• A wall that has been altered by someone before you. Openings formed, thickness reduced, a beam let in. What is on the approved plans and what is standing are not always the same thing.

Which of these you have is not a judgement made by eye. It comes from the title documents, the approved plans held for the property, and a physical survey — and it has to be settled before design, not during construction. Getting it wrong is how a job stops mid-demolition.

What we establish before drawing anything

On an attached house our first pass is deliberately unglamorous:

1. Read the approved plans for both properties where they are available, not just yours. The structural arrangement at the boundary is a two-sided question.
2. Survey the existing wall. Thickness, construction, whether it is carrying load, where the floor and roof structure bears, and whether previous works have already weakened it.
3. Establish the boundary line against the survey plan, rather than against fences, planters and paving — all of which move over the decades and none of which are evidence.
4. Identify every point where the works touch or come near the neighbour: the wall itself, foundations, drainage, scaffolding, the roof abutment, and access.
5. Decide what actually needs the neighbour's cooperation, and separate it from what merely needs their tolerance. They are different conversations.

Only then does the design start. Designing first and discovering the constraint later is the expensive order, and it is the usual one.

The dilapidation survey is the document that protects you

Before any demolition, hacking or piling next to an attached neighbour, the works should begin with a recorded condition survey of the adjoining property — photographs and notes of existing cracks, settlement, floor levels, tile damage and finishes, dated, and ideally agreed with the neighbour.

Every experienced builder in Singapore will tell you the same story: a crack that existed for fifteen years becomes your fault the moment your excavator arrives. Without a dated record of the "before" condition, you cannot prove otherwise, and the argument is not a technical one — it is a credibility one, and you lose it by default.

The survey costs a fraction of one disputed repair. Do it even when the neighbour is friendly, and especially then, because friendly neighbours also sell their houses to less friendly buyers halfway through a project.

The five things that actually cause disputes

1. Vibration

Demolition, breaking, and piling transmit into an attached structure far more efficiently than people expect. The method chosen for your works — how the structure is taken down, what plant is used, whether piling is driven or bored — is partly a neighbour decision, not only an engineering one. We cover the piling side of that in BCA piling approval, monitoring and reporting.

2. Temporary support

If you are removing a load path anywhere near the shared line — taking out a ground-floor wall, forming an opening, adding a storey — the structure needs propping designed for the condition, not improvised on site. This is normal engineering and it is where a licensed builder and a QP earn their keep. The general principles are in load-bearing walls in landed homes and column removal, propping and transfer structure.

3. Water at the abutment

The joint where your new roof, gutter or upper storey meets the neighbour's structure is the single most common source of a post-completion complaint. It is not usually a dramatic failure — it is a slow leak into their bedroom ceiling that appears three monsoon seasons later, at which point the scaffolding is long gone and the fix is difficult and expensive. Detail it properly the first time. Our waterproofing failure points piece covers where these joints go wrong.

4. Access and oversail

On a terrace you frequently cannot build the boundary side of your own house without putting scaffolding, a working platform, or at minimum a person's arm over the neighbour's land. There is no engineering solution to that; there is only an agreement. Ask early, be specific about dates, offer to make good, and put it in writing. A neighbour asked in month one usually says yes. The same neighbour asked in month six, after the noise, usually does not.

5. The works are simply louder than anyone imagined

An attached house transmits noise straight into the next living room. Nothing removes that, but a schedule shared in advance — what is happening, roughly when, and when the worst weeks are — converts a grievance into an inconvenience. It costs nothing and it is the highest-return thing on this list.

What can and cannot be built at the boundary

Setbacks, permitted envelope, roof form and how close you can build to the boundary are planning questions, and they are decided by the controls that apply to your plot, not by what the neighbour built. This is the most common misunderstanding we deal with. The conversation usually opens with "my neighbour did it, so I can too" — and about half the time the neighbour's work was never approved.

That is a genuinely uncomfortable thing to be told, and it is the reason we tell it before quoting rather than after. We would rather lose a job at the enquiry stage than start one that gets stopped. If you have inherited works of unknown status on your own property, that is a related and solvable problem — see what to do about a previous owner's unapproved works.

How the submission handles the boundary

On an A&A to an attached house, the boundary condition is not a side note in the submission — it shapes the structural design. Our architect and Qualified Person are in-house, which matters here specifically: the person drawing the extension and the person carrying the structural submission are looking at the same survey of the same shared wall at the same time, rather than exchanging drawings between three companies and discovering the conflict on site.

We hold a BCA General Builder Class 2 (GB2) licence and are bizSAFE Level 3 certified, and one coordinated quotation covers architect, QP and builder. On boundary work that coordination is not a convenience, it is the risk control.

The order that keeps neighbours on your side

1. Establish the wall and the boundary from documents and survey, before design.
2. Tell the neighbour what you are considering while it is still a sketch, not after approval. People object to being presented with a fact; they rarely object to being asked.
3. Do the dilapidation survey and offer them a copy.
4. Agree access and scaffolding in writing, with dates and a commitment to make good.
5. Share the programme, including the noisy phases, and update it when it changes.
6. Walk the boundary with them at completion and close out anything outstanding while the team is still on site.

None of that is legal protection. It is something better: it usually means there is nothing to protect yourself from.

Talk to us before you commit

If you own a terrace or semi-detached house and you are thinking about an A&A, a storey addition or a rebuild, the useful first conversation is about the boundary — what the shared wall is, what your plot allows, and what will need the neighbour's agreement. We will tell you what is buildable before you spend money on a design that is not.

We do not publish prices for landed structural work, and we explain why in why there is no price list. Every job is quoted after we understand the house.

WhatsApp us about a boundary or party wall →

Related reading: protecting neighbours during demolition and rebuild · URA outline approval before structural work · the A&A timeline from first call to handover