Representative party-wall / SFS junctions have now been tested at full scale. In a recent programme led by voestalpine Metsec at BRE, two junction configurations achieved 90 minutes’ fire resistance, with no adverse heat transfer recorded at the interface. This closes an important knowledge gap. Individual party-wall systems and external SFS wall systems have long been supported by established fire-test data.
For architects, fire engineers, specifiers, contractors and building-control teams, the results provide a stronger and more transparent basis for assessing the continuity of the compartment line.
Why are party-wall / SFS junctions critical to fire safety?
Fire compartmentation depends on the consistent performance of the complete wall assembly. A party wall may have suitable fire-resistance evidence. An external SFS wall may also have suitable evidence. However, the connection between the two introduces changes in materials, linings, fixings, insulation, cavities, seals and installation sequence. These interfaces can become uncertain when products have been tested separately and are then combined on site. The question is therefore not simply whether both wall systems have been tested. It is whether the detail where they meet has evidence to demonstrate that the required performance can be maintained.
Why were these junctions historically untested?
Standard methods such as BS EN 1364-1:2015 provide an established way to assess the fire resistance of non-load bearing wall systems. However, a standard wall test does not automatically address every real-world interface between an internal party wall and an external SFS wall. As Metsec explains in its original article, designers have traditionally relied on conservative engineering judgement when assessing these junctions.
That approach has helped protect safety, but it has also created uncertainty around design responsibility, specification, warranty submissions, installation requirements and the evidence needed to demonstrate continuity at the junction. With greater emphasis now being placed on traceable test evidence and accountable product information, relying on assumption alone is becoming increasingly difficult to justify.
What did Voestalpine Metsec test?
Voestalpine Metsec worked with BRE to construct two large-scale specimens representing common party-wall / SFS external-wall junctions. The specimens were tested following the general principles of BS EN 1364-1:2015. They incorporated representative through-wall and party-wall linings supplied by major UK manufacturers.
The intention was to test details that reflected real construction rather than idealised laboratory arrangements. The programme considered practical factors such as:
- Wall build-up and lining sequence.
- Interface treatments.
- Fixings and installation methods.
- The connection between the party wall and the external SFS system.
- The way the complete junction behaved under fire exposure.
This is important because a junction does not perform as a collection of individual product data sheets. It performs as a complete, installed assembly.
What did the party-wall / SFS junction tests show?
Both tested configurations achieved 90 minutes’ fire resistance. This matched the published performance of the individual party-wall and external-wall constructions used within the specimens. Thermocouples positioned directly at the junction recorded no adverse heat transfer. According to Metsec, this confirmed that the assessed interface did not create a localised weakness or reduce the stability or integrity of the tested wall systems.
The principal findings were:
- Both junction configurations achieved 90 minutes’ fire resistance.
- The junction did not reduce the published performance of the adjoining wall constructions.
- No adverse heat transfer was recorded at the interface.
- The assessed junction behaved as a continuous fire-resisting element.
- The results provide a test-backed reference point for future design decisions.
- The programme replaces an important area of inferred performance with directly tested evidence.
How does Klasse work with Metsec on SFS testing?
Voestalpine Metsec is one of Klasse’s key SFS testing partners. Klasse works closely with leading SFS manufacturers to test and validate external sheathing products as part of complete wall systems. This approach helps demonstrate compatibility, reduce ambiguity during specification and provide architects, designers and contractors with relevant system evidence. These partnerships are built around a shared commitment to fire performance, regulatory compliance and practical construction.
How can Klasse G-board support safer SFS wall detailing?
Klasse G-board is a glass-fibre-faced gypsum external sheathing board developed for light-steel and other framing systems. Klasse G-board is classified as Euroclass A1 for reaction to fire. Klasse also reports tested wall-system performance to EI 120 under BS EN 1364-1 and REI 120 under BS EN 1365-1.
This makes G-board an ideal choice for non-combustible external sheathing within robust, tested SFS wall strategies.Its practical installation characteristics are also relevant to junction safety. G-board is approximately 30% lighter than traditional cement boards and can be scored and cut with a knife for suitable cuts. This reduces reliance on power tools, produces minimal dust and helps installers form accurate details around interfaces.
Further benefits include:
- Euroclass A1 reaction-to-fire classification.
- W1 testing to EN 13859-2.
- Water resistance to BS EN 15283-1 class GM-H1.
- A 12-month exposure guarantee.
- Tested performance within load bearing and non-load bearing wall systems.
- Compatibility with leading SFS manufacturers.
- High density and a published 600 N pull-through strength.Easier handling, cutting and installation than traditional cement boards.
- Suitability for light-steel infill, over sail, modular and light-gauge steel-frame systems.
The junction between a party wall and an external SFS wall has historically been a critical but under-evidenced detail. Metsec’s full-scale testing provides an important step forward. Both representative configurations achieved 90 minutes’ fire resistance, while thermocouples at the junction recorded no adverse heat transfer.
For Klasse, the programme reinforces why we work closely with SFS testing partners such as Metsec and why G-board is developed and tested as part of complete wall systems.
Strong fire-safety assurance does not come from a single product claim. It comes from compatible materials, tested systems, properly detailed junctions, accurate installation and a traceable evidence trail.
This article provides general educational information. Fire-resistance performance depends on the exact tested or assessed wall build-up and should be confirmed for each project.
Credits and source links
Primary technical source and credit: voestalpine Metsec - Closing the Gap: How Tested Party-Wall / SFS Junctions Strengthen Fire Safety Assurance (published 30 March 2026).
This article provides general educational information. Fire-resistance performance depends on the exact tested or assessed wall build-up and should be confirmed for each project.
