A Shift in Approach
Recent years have seen a significant shift in the regulatory requirements for façades and building envelopes.
Post-Grenfell, the immediate response was clear and necessary: focus on fire safety.
Regulations tightened, scrutiny increased, and reaction-to-fire performance became the defining metric, with the regulatory requirement for A1 and A2-s1,d0 classifications driving the selection of compliant products.
This increase in regulatory rigour has clearly delivered real improvements, including the development of Class A membranes and façade sealing systems. And buildings are undoubtedly safer as a result.
But in sharpening one lens, we blurred another. We unwittingly created a counterproductive imbalance by focusing almost solely on fire performance, with other essential aspects of façade performance often overlooked.
The materials that make up a façade must not only manage fire risk, but also contribute to moisture control and manage air and vapour movement. Each of those features plays a critical role in a building’s safety and integrity, and neglecting them carries serious risks.
Why Moisture Control Is Back in Focus
So what we are seeing now are these elements being brought back into sharper focus.
Unlike fire, moisture issues usually develop gradually. But their effects are just as serious. Water can enter through joints, penetrations, or exposure during construction, and without proper control, it becomes trapped within the wall build-up.
Sheathing boards, even when tested and certified, are not designed to act as a complete weather barrier. Their joints and fixings create natural points of vulnerability, particularly in real-world site conditions.
When moisture is not properly managed, the consequences are well understood:
- Material degradation
- Internal damp and mould growth
- Reduced thermal and structural performance
But above all, we cannot ignore the human impact of this.
The tragic death of two-year-old Awaab Ishak in 2020, after prolonged exposure to mould in his home, brought national attention to the real risks associated with poor moisture control.
It demonstrated clearly that moisture control is not just about technical performance; it directly affects occupant health and safety.
In fact, if not addressed, it could become just as much of a risk to human life as fire is.
Where Breather Membranes Come In
This shift in thinking helps explain the renewed clarity around breather membranes.
The part they play in ensuring the integrity of a façade is not new. They provide a critical layer of weather protection, helping to prevent water ingress while allowing moisture vapour to escape from within the wall.
What has changed is how this is understood and how consistently it is being applied. When it comes to meeting minimum performance requirements, warranty providers are unequivocal:
- LABC Warranty:
“Breather membranes are required for all framed structures… placed on the external face of the sheathing board to help maintain weather performance during construction.”
- Premier Guarantee:
“A breather membrane must always be installed, irrespective of the external sheathing board product.”
These statements are from leading warranty providers whose requirements will clearly supersede any claims that a manufacturer may make about their products. Claims of ‘membrane-free’ solutions simply don’t align with warranty expectations.
A Long-Range View of ‘Safety’
The direction of travel is clear.
The industry is recognising that the safety of a compliant façade can’t be reduced to a single characteristic ie. managing the fire risk. Moisture control, vapour and air control and long-term durability, are interdependent and of equal importance.
And designing for that from the outset is now simply part of delivering safe, compliant and durable buildings. Because when it comes to safety, there can only be one standard.
What to Consider
For Architects
- Design holistically: Don’t specify on fire classification alone – consider how each component contributes to moisture, air and vapour management.
- Assume real-world conditions: Site exposure with good old British weather, product sequencing, and good workmanship matter. Design for them, not against them.
- Consider membranes as essential: A core part of the wall build-up that ensures long-term integrity of the whole building.
- Think system, not just product: Compatibility between layers is what defines performance.
For Main Contractors
- Protect during construction: Temporary exposure is a key risk – ensure membranes are installed early and correctly.
- Challenge ‘membrane-free’ claims: Warranty requirements will always take precedence.
- Prioritise installation quality: Even the best specs fail with poor execution. On-site training by product manufacturers makes the difference.
- Work with proven systems: Tested, compatible solutions reduce risk across potential fire and moisture issues, for long-term durability.