WATER TREATMENT, DRAINAGE & PIPED SERVICES


Whole-system accountability: the specification question nobody asks until it leaks


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Arne Glass, specification manager at Brymec, makes the argument for whole- system thinking at specification stage to protect installations from future insurance claims


ccording to the Association of British Insurers (ABI), escape of water claims costs UK insurers oughly £2.5 million every day1, which is a potentially eye-watering


headline figure Aviva puts the share of UK construction sites that experience water damage at around 65%2. Behind both these statistics sits the same question: when a building leaks after handover, who carries the design liability? The Building Safety Act 2022 provides a statutory answer to that question. The Act places a Principal Designer on every project with a positive duty to coordinate all designers and verify the full design package meets Building Regulations. If that role is yours, or your name is on the specification, you’re accountable for system compatibility.


The clause that quietly rewrites the spec


The ‘equal or approved’ clause was designed for flexibility. In practice, it has become the primary vehicle for compatibility risk on UK projects. Late swaps driven by cost rather than performance are not unusual. They are routine. The original specification, written around a particular manufacturer’s tested assembly, gets rewritten one swap at a time. Often those changes go undocumented. By handover, what was specified and what was installed may share a product category but not a tested compatibility envelope.


Individual component certification is not the same as a tested system. Products assembled across multiple manufacturers cannot be assumed to form a compliant assembly simply because each element reached its own standard. The interfaces between them have not been tested. Nobody holds the warranty for those joints.


This is not an edge case. It is how substitution works in UK procurement. Under the Building Safety Act 2022, an undocumented substitution transfers design liability to whoever authorised the change. But without a written record of objection, the original specifier’s exposure does not simply disappear. The Act does not reward silence.


Why warranty terms are the problem, not the solution


Building services engineers understand technical specifications. Fewer read manufacturer warranty documents with the same rigour. They are commercial instruments, drafted to allow claims to be challenged. Take the Brymec Stainless Steel Press-fit System as a worked example. It carries a warranty of up


to 30 years, conditional on certain requirements: a current training certificate issued by Brymec, approved press tools maintained to the manufacturer’s requirements, installation on Brymec 316L stainless steel tube, and retained commissioning paperwork. Miss one condition and the warranty is challengeable. Let’s apply the substitution scenario. The specified system is replaced on procurement grounds. The installer, trained on presses from system A, is now fitting system B, potentially with tools the replacement manufacturer has never approved. Eighteen months later, a joint fails above a server room. The replacement manufacturer finds no training certificate for their system and declines the claim. There is a secondary issue that rarely gets discussed. Even where claims succeed, manufacturer terms typically exclude liability for indirect and consequential loss. According to analysis from the Uptime Institute3, a £10 fitting failure can cause hundreds of thousands of pounds in water damage and downtime to a data centre fit-out. Yet, often it does not result in an equivalent warranty payment. It starts an argument about who owns the damage; one that follows the liability chain back to whoever approved the change.


Mixed materials, unmeasured movement


The thermal dimension is underappreciated at design stage. Plastics expand at a significantly higher rate than metals under


26 BUILDING SERVICES & ENVIRONMENTAL ENGINEER AUGUST 2026


temperature change. That differential places joints under sustained stress. Seals weaken and connections come apart gradually, with no visible sign at commissioning. These failures surface typically in occupation, often two or more winters in, when access costs have multiplied and remediation is compounded by the building being in use. Thermal movement is rarely calculated across all manufacturers’ components. It is calculated per product, not across the system. For a design engineer, this is a specification decision, not a site decision. Any interface crossing a manufacturer boundary, whether plastic to metal or cast iron connecting to HDPE drainage, needs an owner in the specification. If the spec does not name one, procurement will resolve it by price.


Who carries the liability misalignment?


The cost saving from a substitution might sit in one party’s budget while the approval moves through another’s submission process; sometimes this prompts legal disputes over where responsibility for the risk ultimately resides. Specifiers are being asked to demonstrate genuine design assurance, not generic clauses. When an original specification gets quietly rewritten through undocumented substitutions, the clause meant to preserve design intent becomes the mechanism by which design assurance disappears.


Read the latest at: www.bsee.co.uk


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