Introduction
In this article we consider snag propensity testing – a critical factor when specifying roofing membranes. We look at the testing dynamics, why it is important and why choosing a tested solution is important. We highlight the legalities of bat protection and conservation and membrane manufacturers’ ecological responsibilities.
Bat Conservation and Ecological Responsibility
All species of bat, their breeding sites and roosts are protected in the UK. In England and Wales under the Wildlife and Countryside Act 1981 (as amended) (‘the W&CA 1981’) and the Conservation of Habitats and Species Regulations (2017) (‘the Habitats Regulations’) and in Scotland by the Conservation (Natural Habitats, & c.) Regulations 1994 (as amended).
In the UK, the law protects all bats and their roosts due to the serious decline in numbers over the past century, predominantly because of the loss of suitable roost sites and feeding habitats (Entwistle et al, 1997), or disturbance and change of use of man-made roosts (including buildings) (Kunz and Reynolds, 2003).
In the Republic of Ireland, bats are protected under the Wildlife Act 1976 and subsequent amendments, whilst in Northern Ireland, bats are protected under the Wildlife (Northern Ireland) Order 1985. In both jurisdictions there is a similar level of protection; it is an offence to intentionally disturb, injure or kill a bat or disturb its resting place and any work on a roost must be carried out with the advice of the National Parks and Wildlife Service in the Republic, or the Northern Ireland Environment Agency in Northern Ireland.
This protection is irrespective of the number, species or how long they have been using the building. Roosts remain protected all year round whether occupied or not, since bats sometimes use a roost for only part of the year, they are often very loyal to these roosts and will return each year at the same time. It is illegal to disturb or harm bats, or damage, destroy, or obstruct a roost, whether the person had prior knowledge or not.
A substantial proportion of bats rely on buildings and specifically roofs for roosting; this makes them vulnerable to changes in building materials. During roosting, bats physically interact with the surface of roofing membranes through the gaps between battens and in the roof space. Their claws can snag the surface of the non-bitumen coated roofing membrane (NBCRM), which can cause loops of continuous filaments to be teased free from the fabric structure to produce surface ‘fluffiness’. Since 2004, concerns have been raised about the level of bat mortality (Waring et al, 2013; Waring, 2014) as they are often caught in these loose, strong filaments and can become fatally entangled.
The presence of bats in buildings cannot be reliably ruled out at design stage, particularly in retrofit projects where roof voids and concealed spaces are already established.
Everyone involved in construction, maintenance or pest control should know what signs to look out for and what to do if they find bats or signs of bats during work. Equally it is important to consider what construction materials to use in areas where bats may decide to roost in the future.
Bat Conservation
The Bat Conservation Trust supports local bat groups across the UK with circa 5,000 members. The trust collaborates with volunteers, scientists, industry and government both locally and nationally on a range of projects to ensure a world in which bats and humans can thrive together. Key for the construction industry and the application of breather membranes in particular, is the Trust’s work on how bats use the landscape and how the industry can engage in their conservation with progressive construction practices, by understanding their ecological importance and protection.
Snag Propensity Evaluation and Testing
As suggested, material selection should be considered carefully and in terms of roofing membranes and only non-bitumen coated roofing membranes (NBCRMs) should be specified. This was because of research that had revealed that all non–woven roofing membranes, produced using spun-bond filaments could pose a serious threat to bats as a result of entanglement.
NBCRMs are both breathable and non-breathable roofing membranes and are ideal to meet modern airtightness and energy efficiency standards in line with the Government’s net zero strategy.
Since 2019 the NBCRMs steering group has been working to find pragmatic solutions to the use of energy efficient materials within roost spaces, including publishing a test methodology for the snagging propensity of NBCRMs. By helping companies bring to market ‘bat safe’ roofing membranes that address the climate change and energy efficiency issues in our buildings, the steering group hope to reduce the industry’s reliance on roofing membranes that can pose a serious threat to bats.
Method for evaluating the snagging propensity of roofing membranes in buildings by roosting bats
In 2020, The Bat Conservation Trust (BCT), the Special Nature Conservation Orders (SNCOs) and academics from the University of Reading (Dr. Emmanuel Essah) and University of Leeds (Prof. Steve Russell) published their paper on Non-Bitumen Coated Roofing Membranes methods testing in Building Research and Information journal.
Titled ‘Method for evaluating the snagging propensity of roofing membranes in buildings by roosting bats’ (E. Essah et al 2020) this methods paper allows the independent testing of membranes to answer the question of what constitutes a roofing membrane with minimised risk to bats from snagging propensity.
Building regulations require all construction materials to be fit for purpose, but some breathable roofing membranes, although appropriate for their intended purpose, can potentially threaten the viability of existing, legally protected roosts because of the way bats physically interact with their surface.
With the assistance of the Isle of Wight Bat Hospital and real-world observations of how bats physically interact with NBCRMs within a roof void, a laboratory test method was produced which reproduces the progressive disintegration of NBCRM surfaces due to the plucking effect of bat claws.
The resistance to NBCRM disintegration was characterised using a modified laboratory fabric pilling box test method. The method reproduced the ‘fluffing’ effects and projections of loops of filaments on the surface of BRMs that have been observed within bat roosts. It was established that spunbond nonwoven BRMs, can be highly susceptible to surface disintegration. The newly developed method is intended to aid selection of NBCRMs that reduce the risk to bats in their roosts, promoting bat conservation.
In simplistic terms the test measures how likely a membrane is to catch or entangle, particularly with bat claws as these fibres on certain membranes pose a serious risk to roosting bats.
In retrofit scenarios, this consideration moves beyond best practice and becomes critical risk mitigation, where inappropriate specification can lead to project delays, regulatory intervention and increased costs.
Retrofit and Conservation Constraints in Roofing Projects
Retrofit Complexity and Conservation Constraints
Roofing retrofit projects, particularly within conservation or heritage buildings, present a set of constraints that extend far beyond standard material specification.
Unlike new build construction, retrofit works are inherently reactive. Existing structures often conceal unknown conditions, and the presence of protected species such as bats introduces additional layers of regulatory, ecological and programme risk.
In practice, several key bottlenecks are consistently encountered:
Uncertain Site Conditions
Pre-construction surveys may not always identify active or transient bat roosts. Bats can occupy buildings seasonally, meaning their presence may only become apparent once works have commenced. This creates a significant risk of unplanned disruption.
Programme Delays Due to Ecological Restrictions
Where bats are identified, works may be legally required to stop immediately. Mitigation measures, licensing applications and ecological supervision can delay projects by weeks or months. Seasonal constraints, particularly during maternity roosting periods, can further restrict when works are permitted.
Licensing and Compliance Complexity
Any work affecting bat roosts requires engagement with statutory bodies such as the National Parks and Wildlife Service or Natural England. The licensing process is detailed and time sensitive, often requiring ecological assessments, method statements and approved mitigation strategies before works can proceed.
Material Constraints in Heritage Buildings
Conservation requirements may limit the ability to alter roof build ups or introduce modern materials. Breathable membranes must balance vapour permeability with durability, while also ensuring compatibility with traditional construction methods. This creates a narrow specification window.
Conflict Between Performance and Conservation
Improving airtightness and energy efficiency is a primary driver in retrofit. However, poorly selected materials can introduce ecological risk, particularly where bats interact with membrane surfaces. This creates a tension between compliance with building performance targets and biodiversity protection.
Increased Contractor Liability and Risk Exposure
Failure to identify or appropriately manage bat presence can result in legal consequences, project delays and reputational damage. As a result, contractors and specifiers must adopt a precautionary approach, selecting materials that minimise risk even where bat presence is not confirmed.
Why This Matters for Membrane Specification
Within this context, membrane selection becomes a risk management decision as much as a performance specification.
Specifying membranes with proven resistance to snagging propensity reduces the likelihood of ecological harm, supports compliance with conservation legislation and helps avoid costly disruption during retrofit works.
EXOPERM DURO 300 Fuse Breather Membrane
Partel has developed EXOPERM DURO 300 Fuse, a high strength, diffusion permeable breather membrane designed for facade and roof applications where durability, vapour control and weather resistance are key. Independently tested for snag propensity, EXOPERM DURO 300 Fuse is fully aligned to bat safe construction, an important consideration particularly in retrofit projects.
Test Profile and Results
Leeds Institute of Design and Colour performed the snag propensity testing of EXOPERM DURO 300 Fuse, with the membrane sample tested both on the front and back as outlined in Essah et al., 20201 at 1,000 rotations. Following the modified pilling test for both sides of the membrane, EXOPERM DURO 300 Fuse showed no evidence of loop formation on either side.
Other Key Features
Engineered for strength, dimensional stability, and resilience, EXOPERM DURO 300 Fuse performs reliably under challenging weather conditions and extended UV exposure. This high-performance membrane combines exceptional tensile and tear resistance with outstanding vapour permeability, allowing buildings to breathe while being airtightness and watertight.
Its durable construction ensures consistent performance over prolonged temporary exposure, making it suitable for both new build and retrofit projects, as well as modular or offsite construction where membranes may be exposed before cladding or roofing is installed.
With dependable W1 water resistance, the membrane provides a secure barrier against rain and wind, while its vapour openness supports healthy indoor environments, reducing the risk of condensation and long-term moisture damage.
Conclusion
The key factors to consider when aligning breather membrane specification and bat conservation are:
- Buildings may already host protected bat populations
- Unsuitable materials can cause harm or fatal entanglement
- Retrofit works must balance performance with biodiversity
- Legal and environmental responsibilities must be considered
EXOPERM DURO 300 Fuse has been developed to address these challenges directly, combining durability, vapour permeability and independently verified resistance to snagging propensity. This highlights Partel’s focus on developing technologically advanced, high-performance products whilst also aligning the company’s ecological responsibilities.
References
https://eprints.whiterose.ac.uk/id/eprint/160163/1/BRI-20BR2180-RE.R1-Accepted%20Version.pdf
https://www.bats.org.uk/our-work/buildings-planning-and-development/non-bitumen-coated-roofing-memb…
https://www.bats.org.uk/advice/im-working-on-a-building-with-bats
https://www.bats.org.uk/advice/bats-and-the-law
https://www.batconservationireland.org/irish-bats/protection-law
https://www.bats.org.uk/our-work/national-bat-monitoring-programme
https://shopeu.partel.com/products/exoperm-duro-300-fuse-breather-membrane
