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The Blog of a Ranting Zoologist
Its What's on the Inside that Counts!!!
This is a brief post between thesis chapters just to mention another report of problems regarding certain types of bitumen felt.
The problem has arisen where bitumen felt reinforced with polypropylene spun-bond filaments has been fitted. It is assumed at present that this is Type 5U (see previous post) but this is yet to be confirmed. From the phtos below I can count at least 20 dead bats…both adults and juveniles. So again this was a maternity roost.
This just goes to show that the materials specified in bat roosts really needs to be thought through and then enforced. These spun-bond filaments are being used more and more, not just in breathable membranes but in modern Type 1F replacements and now in some types of bitumen felt.
The ONLY material we can say is safe for bats at present is BITUMEN TYPE 1F felt. If it says any of the following words -
Then it is not suitable and could lead to the entanglement and death of bats. Please pass this on or contact me with any information
Type 1F or Type 5U: Are both safe for bats?
Over the past two weeks I have had three different emails regarding the use of Type 5U bitumen underlay within bat roosts. Up until this point I had given very little consideration to the fact that there are different types of bitumen felt on the market. I will admit this is due, in part to my own lack of knowledge but also the fact that Type 5U felt is very rarely mentioned.
Throughout literature referencing bitumen underlays, Type 1F (In accordance with BS 747:2000 or BS 8747:2007 as it is now) is the standard that is often quoted. However, Type 5U is also mentioned in both of these British Standards and is suitable for use as a roofing underlay……..Sooooo? I hear you ask.
Well, at present we consider bitumen felt to be a safe option for use in bat roosts. However, up until this point it has always been assumed that when we specify bitumen felt, it will be of the Type 1F variety. It would appear this is not the case and Type 5U holds a dark secret.
The below descriptions are taken from BS 8747:2007 -
Sheet comprising a bitumen-impregnated and coated fibre base combined with a layer of jute hessian, embedded in the coating on one side of the base so as to reinforce and strengthen the sheet. The sheet is coated with a fine surfacing material to prevent the product sticking in the roll. The presence of the hessian is obvious on inspection.
The base, consisting of animal or vegetable fibres made into a close-textured absorbent sheet of fibre.
These two images show the front and back of Type 1F felt (respectively). The hessian/jute base can be seen in the second photo.
The sheet comprises a bitumen-impregnated and coated polyester base, covered with a fine surfacing material on both sides to prevent the product sticking in the roll. The polyester base provides improved performance capability of the product due to its greater reinforcing properties and mechanical strength.
The base consists of a non-woven sheet of polyester staple fibres or polyester continuous filaments.
These two images show the front and back of Type 5U felt (respectively). There is no visible matrix on the back side of the felt, this means that the reinforcing matrix is embedded throughout the product.
When I first started looking into the question of ‘what is the difference between these two underlays?’ and 'are they both safe for bats?’ it had been quite difficult to find an answer on Google. So having turned to the British Standards I saw the dreaded words 'non-woven’ and 'continuous filaments’. For anyone who is familiar with my research, these descriptions are more commonly associated with breathable roofing membranes (that pose an entanglement risk to bats).
Before this point I had believed the polyester matrix in 5U would be similar in design to the hessian matrix in 1F, but upon seeing this new description I ordered a roll of the product for comparison.
This image shows the hessian matrix pulled free from the 1F felt. It is in the form of loosely woven yarns that pull free as an entire 'string’ of material.
This second image shows the polyester filaments within the 5U felt. Whilst there are some yarns, the main reinforcement of the product comes from continuous filaments that have been laid down and coated in bitumen. These filaments run throughout the product and it is extremely difficult to remove a single section.
Why is this a concern?
In the past there have been only a couple of reports of bats becoming trapped in bitumen felt. The majority of entanglement issues come from the use of non-woven breathable membranes in bat roosts. Until this point we have considered bitumen felt a safe option, but this was based on the belief that 1F felt would be the product used when bitumen felt was specified.
Following the queries in the past couple of weeks it is now obvious that this isn’t always the case, and so it is important to consider whether bitumen felt reinforced with spun-bond polyester could pose an entanglement threat, as seen with spun-bond polypropylene products.
It could be that the bitumen holds these filaments together and so they are never exposed enough to form the 'fluff’ that in other scenarios could lead to entanglement, however, it could also be that as the bitumen felt ages, the filaments are exposed and could become tangled around a bats feet and thumb claws. This has been seen in extreme cases where 1F has been degraded and the hessian matrix frayed and exposed. If this happened in Type 5U the risk of entanglement would surely be much greater?
I do know that the membrane I received earlier this year (that trapped 104 pipistrelle bats), was a spun-bond non-woven product that had a very thin bitumen coat.
This goes to show that in this situation, the filaments has been pulled free from the bitumen coating and have caused the deaths of a large number of bats.
Could this happen with Type 5U?
The answer is I don’t know but it definitely needs more research!
Thanks for reading and those of you who managed to make it through this blog without the thought of Keanu Reeves in slow motion action shots, deserve a cuppa tea and a biscuit!!