The developer who asked the right question
A developer on a zone 2 London scheme asked their architect one question before sign-off.
"If the terrace leaks in year ten, who pays?"
The architect had no answer. The question changed the specification.
The question most developers do not ask
Most developer conversations about roof terrace specification focus on three things: programme, cost, and planning. The structural and waterproofing detail is treated as a technical matter for the architect and engineer to resolve. The developer approves the budget and the programme and trusts that the professionals have made sound specification decisions.
This is a reasonable position. Developers are not structural engineers. They should not need to interrogate the fixing detail of a balustrade specification.
But they should ask one question. Not the technical question - that is the architect's job. The commercial question: if this terrace creates a water ingress problem in five or ten years, what is the liability chain? Who is contractually responsible? Who has the warranty? Who pays for the remediation above the occupied apartments?
Why the answer is usually uncomfortable
On a project where the balustrade has been penetratively fixed through a waterproofed membrane, the honest answer to that question is: nobody clearly.
The membrane manufacturer's warranty has in most cases been voided by the third-party penetrations. The balustrade supplier has fulfilled their contract. The waterproofing contractor has signed off their work. The structural engineer has calculated the fixings in isolation. The architect has coordinated the trades but has not formally certified the interface between them.
When water ingress occurs - and on penetratively-fixed roof terraces above occupied space, it is a question of when rather than if - the liability question that the developer should have asked at specification stage becomes a legal dispute between parties with competing contractual defences. The developer, who holds the asset and the leasehold obligations, frequently ends up funding the remediation while the legal argument plays out.
What the right question produces
The developer on the zone 2 scheme asked the question before sign-off, not after water appeared. The architect's honest answer - that the liability for the penetrative interface was distributed across multiple parties without a single point of ownership - prompted a specification review.
BalcoDeck was introduced at Stage 4. The structural calculation was reviewed by the project engineer and accepted. The specification was changed. The developer received a single Certificate of Compliance at handover, from one company, covering the complete balustrade and deck system. The membrane warranty remained intact alongside it.
The question every developer should ask
Before any roof terrace specification is signed off on a residential or mixed-use development: who is liable if this terrace leaks in year ten, and what documentation exists to support that liability position?
If the answer requires a conversation between the membrane manufacturer, the waterproofing contractor, the balustrade supplier and the structural engineer - and if none of those parties have formally signed off the interface between their work - the specification needs to be reviewed.
The question takes thirty seconds to ask. The answer, if it reveals a problem, is worth considerably more than thirty seconds of attention before work starts.
