Breather membranes are used in roof and wall installations to ensure long-term protection to the building envelope. Breather membranes offer water repellent properties combined with high water vapour permeability to  control condensation within the building’s interior. Specialist breather membranes with additional characteristics, such as  high UV resistance, ventilation control and energy efficiency, are also beneficial  for the building’s long-term protection.

Breather membranes perform various key functions. Firstly, they allow the easy release of excess moisture vapour into the atmosphere. This functions keeps the internal wall/roofing structures dry.  Secondly, breather membranes protect against the ingress of dirt, dust and rain which are especially problematic when coupled with driving rain. Some systems also provide protection against the impact of solar light and heat.

Breather membranes must perform these protective functions without compromising their breathable qualities. Breather membranes are installed between the insulation and the outer wall layers (e.g, cladding or roof tiles). If they protect from external conditions without being sufficiently  breathable, the naturally occurring moisture within the building will be trapped in the interstitial layers. This will be highly damaging in the long term.

British and international building standards specify flame retardant materials for specific installations and structures. Flame retardant additives are incorporated within the materials or added as a coating to make them flame retardant; it is the formulation, quality and amount of these additives that determine which flame retardant tests the material will pass and what standards to which they will comply.

A flame retardant material is one that self-extinguishes; it does not mean that it is flame proof. Flame retardant materials are resistant to catching fire, reduce flammability, and inhibit, suppress or delay the production of flames. Flame proof materials are ones that are not liable to catch fire or be damaged by fire and are not readily ignited or burned by flames.

In 2002, to harmonise the classification of the reaction to fire for building materials, the European Commission introduced the Euro Fire Class System (Euroclass) based on EN ISO 13501-1. 

Current regulations require an external wall construction over 18m to have a minimum Euroclass A2-s1,d0 fire safety rating. However, breather membranes are currently exempt from being part of an A1 or A2-s1, d0 vertical wall system; they are required by law a minimum Euroclass rating of B,s3-d0. In Scotland, this requirement applies to external wall constructions over 11m.

Following the introduction of the Building Safety Act in 2022, the latest regulations are subject to ongoing review and the construction industry should plan for further regulatory change. Best practice recommends the use of breather membranes which have a Euroclass A2-s1,d0 fire safety rating in line with the requirements for cladding and other external wall materials.

STANDARDS

*Indicative purposes only; test methods and standards vary

EN 13501-1 STANDARDS

To meet the requirements for EN ISO 13501-1, the Euro Fire Class System, two test standards must be passed.

EN 11925-2

Single Flame Source Test “Reaction to fire tests for building products— Part 2: Ignitability when subjected to direct impingement of flame.” The method specifies a test for determining the ignitability of products by direct small- flame impingement under zero impressed irradiance using vertically oriented test specimens.

Although the method is designed to assess ignitability, this is addressed by measuring the spread of a small flame up the vertical surface of a specimen following application of a small (match-sized) flame to either the surface or edge of a specimen for either 15sec or 30sec. The determination of the production of flaming droplets depends on whether or not the filter paper placed beneath the specimen ignites.

Pass standard:

• Flame spread (Fs) <150mm within 60sec (when exposure time is 30sec)

EN 13823

(SBI) Single Burning Item (SBI) Test “Reaction to fire tests for building products—Building products excluding floorings exposed to the thermal attack by a single burning item.” A method of test for determining the reaction to fire behaviour of building products (excluding floorings) when exposed to the thermal attack by a single burning item (a sand-box burner supplied with propane). The specimen is mounted on a trolley that is positioned in a frame beneath an exhaust system. The reaction of the specimen to the burner is monitored instrumentally and visually. Heat and smoke release rates are measured instrumentally and physical characteristics are assessed by observation.

Pass standards:

• Fire Growth Rate Index (FIGRA) must remain below 120 W/s
• Total Heat Release (THR) in the first 600sec of exposure must be <7.5MJ
• Lateral Flame Spread (LFS) must not reach the edge of the specimen, the
  flame spread (Fs) must be <150mm within 60sec