Fire regulation 2026: the through-wall evidence test

What is actually changing in fire regulation?

Three movements are converging. On 30 September 2026, amended Approved Document B guidance introduces a second-staircase provision for new residential buildings over 18 metres, subject to transitional arrangements. The Building Safety Regulator's 2026 review of Approved Document B goes wider, examining evacuation lifts, specialised housing, combustible structural systems, external walls and balconies, roofs and photovoltaics, car parks and the treatment of BS 9414 assessments. In parallel, the government's Construction Products Reform White Paper proposes reform of testing, certification, product information and enforcement.

For envelope teams, the common thread is not simply “more fire-rated products”. It is greater scrutiny of whether the evidence applies to the wall that is actually being designed, procured and built.

Why is product-by-product compliance no longer enough?

A façade is an assembly of interacting layers: internal lining, SFS, insulation, sheathing, membranes, cavity barriers, fixings, rails, cladding, windows and the seals between them. Each may carry a declaration, classification or certificate. That stack of documents does not automatically describe the performance of the combined wall.

The distinction matters because different tests answer different questions. EN 13501-1 classifies reaction to fire. Fire-resistance tests examine integrity and insulation for a defined assembly. BS 8414 evaluates external fire spread in a large-scale façade configuration, with BR 135 providing performance criteria. Assessments and extended fields of application may bridge some variations, but only within a reasoned and documented scope.

The BSR's 2026 consultation makes the principle explicit: test evidence used to support a product or system should be checked for applicability to its intended use. That is a technical instruction with commercial consequences. A cheaper substitution is not equivalent because its headline classification matches; an interface omitted from the test is not covered because it is small.

What has advanced in through-wall systems?

Manufacturers are increasingly testing and certifying multi-layer wall configurations rather than leaving designers to assemble unrelated product evidence. OBEX, for example, publishes CORTEX through-wall configurations with stated EI60, EI90 and EI120 fire-resistance performance and says its test programme includes breather and air-and-vapour-control membranes. Its interface-sealing range also carries product and system documentation, including BBA certification for defined membrane and adhesive configurations.

That is a useful development because membranes and interfaces have historically been treated as secondary details despite controlling air, water and vapour continuity and forming part of the fire strategy. Bringing them into the tested assembly reduces an evidence gap.

It does not remove project judgement. The BBA certificate itself illustrates the discipline required: classifications apply to the build-up tested, and some results are expressly limited by substrate, adhesive, application rate or air-gap arrangement. The right question is therefore not “is this an OBEX system?” It is “does the proposed configuration sit inside the evidence, including every interface and fixing condition?”

What does a through-wall warranty add, and what can it never add?

The phrase “through-wall warranty” is used inconsistently. It may mean a single-source product warranty, a system-performance warranty, design support, installation audit or some combination. Before relying on one, the client and principal designer should ask:

1. Which legal entity gives the warranty, and for how long?
2. Does it cover products only, or design, compatibility and installation too?
3. Is the exact project build-up scheduled, including windows, slab edges, parapets and penetrations?
4. Which test reports, classifications, assessments and third-party certificates define its scope?
5. What inspections, approved installers and photographic records are conditions of cover?
6. What happens when a component changes after Gateway 2?
7. Are consequential loss, access and replacement costs excluded?

A warranty can align responsibility and improve technical support. It cannot turn an out-of-scope configuration into a tested one, transfer a dutyholder's statutory duties, or guarantee BSR approval. Treat it as a contractual layer over technical evidence, not as the evidence itself.

What should the Gateway 2 envelope submission contain?

The useful unit of information is the wall type, not the individual product. For each wall type, provide a controlled drawing and schedule linking every layer and interface to the compliance argument. Include the fire strategy requirement; system test and classification reports; field-of-application limits; cavity-barrier and fire-stopping details; hygrothermal and condensation analysis; structural movement assumptions; window and curtain-wall interfaces; installation sequence; inspection points; and the change route.

Record assumptions openly. If an engineering assessment is used instead of direct test evidence, identify who authored it, their competence, the supporting test series and the limits of the conclusion. If a warranty is relied upon, append its proposed scope and conditions rather than merely naming the provider.

What changes at Gateway 3?

At completion, the design case has to meet the installed building. Batch references, delivery records, installer competence, inspection photographs, cavity-barrier sign-off, fire-stopping records and commissioning evidence should reconcile to the as-built wall schedule. Any departure from the approved configuration needs a controlled-change record and an updated technical conclusion.

The advance in through-wall testing is real. Its value is lost if the procurement and site record cannot prove that the tested system is the one behind the finished façade.