Warning Batsafe is NOT bat safe

[Jilly]

Take care,  my builder ordered £1k worth of TXL Batsafe membrane, and it isn't bat safe at all and has to go back. Only F1 bitumen will do.

 

 

Edited September 1, 2020 by Jilly
extra info

[PeterW]

I take it you have high levels of bat activity then ..?? Is this the ecology officer who has said no.?

[Jilly]

We found just one pipistrelle bat when the building was stripped...

 

The ecology officer has said no, but there is lots of controversy about this product when you look for it.

 

Builder is now worried about ventilation and how to square it with BC

 

[joe90]

In our planning fight our ecologist agreed that I could build bat boxes into the roof of my workshop to stop having bats in the house, planners said we still want them in the house. At the appeal the gov inspector told the planners they were not qualified to over rule the ecologist ?

[willbish]

If you use a sarking board and then a modern membrane on top the ecologist can't see the membrane from inside the attic space....

 

Not that I have applied this approach ?

[Jilly]

I agree it's bonkers that I have to invite bats in where there were none. Or wasps...

[Big Jimbo]

I feel very lucky. I see bats every evening in the garden. With my knock and build i'm not required to have any reports bat or otherwise.

[joe90]

2 hours ago, Jilly said:

I agree it's bonkers that I have to invite bats in where there were none. Or wasps...

If you had no bats why are the planners making you cater for them???

[Jilly]

Good question. The bats were in the featherboarding and will have nice new homes there too,  should they chose to use them...

[joe90]

3 minutes ago, Jilly said:

The bats were in the featherboarding

Ah! so you did have bats, so did we but I was able to move them out to the workshop with the help of the ecologist.

[Jilly]

We found one during the hand strip (which has cost about £6k altogether) (not that I'm sore about it, can't you tell?), but we have to accommodate them back into the building. Didn't you have to? 

[joe90]

23 minutes ago, Jilly said:

Didn't you have to? 

No, the ecologist supported my option of housing them I’m my detached workshop roof (even tho the planners wanted them in the house as well).

[Conor]

1 hour ago, joe90 said:

No, the ecologist supported my option of housing them I’m my detached workshop roof (even tho the planners wanted them in the house as well).

 

That's exactly what we are doing. I'm using bat friendly cladding and roofing on a shipping container workshop in the garden.

 

In these situations, the planners are meant to follow the guidence of the relative experts.

 

[Jilly]

19 hours ago, Conor said:

 

 I'm using bat friendly cladding

 

Mmm, my point is that the stuff which claims to be bat safe isn't. Anything which is breathable polyester based stuff tangles in their feet and traps them. There are lawsuits going on, not surprisingly, about the misleading name. But imagine if we had put the stuff on, finished the roof, then the ecologist had demanded that we use F1 bitumen (the only really safe stuff, apparently). What a who ha of blame that would be. 

As it is, it's had to be bounced back to the architect, as BC wouldn't comment about the need for a different ventilation solution. Watch this space. 

 

 

[Temp]

On 01/09/2020 at 12:50, Jilly said:

Builder is now worried about ventilation and how to square it with BC

 

Typically you either need a vapour permeable membrane or a 50mm ventilated void below a non permeable membrane. The latter causes issues with the depth of insulation between rafters. You may need more insulation below the rafters. 

 

An alternative might be to switch to a warm roof which puts insulation above the rafters but raises roof height. That doesn't need ventilation but it's important to get an interstitial condensation risk assessment done for the proposed design. Don't let the builder just wing it.

[JamesP]

I have had to provide 72 sqm of bat roost in the garage roof all lined with Bitumen F1. And a heater. The joy.

[Jilly]

19 hours ago, Temp said:

 

Typically you either need a vapour permeable membrane or a 50mm ventilated void below a non permeable membrane. The latter causes issues with the depth of insulation between rafters. You may need more insulation below the rafters. 

 

An alternative might be to switch to a warm roof which puts insulation above the rafters but raises roof height. That doesn't need ventilation but it's important to get an interstitial condensation risk assessment done for the proposed design. Don't let the builder just wing it.

Thank you, I think this answers the question, apart from the fact we are a conversion in a conservation area and can't change anything...

[Wil]

Just to come back to this, we’re now in the situation of having to insulate roofs where there may or may not be bats under the tiles (emergence survey had a single possible). I have permission to raise the roof, but the builder doesn’t like the idea of 150mm celotex over the rafters (too hard to fix apparently) and had been planning 75over and 75 in between. Then a bat safe (tlx?) membrane over the lot. This is what our batman has recommended. 

 

My concern is having to put bitumen felt back on and also trying to put 75mm celotex in between existing wavy 100mm deep rafters and it have any effect.

 

Spoke to Ecomerchant and they won’t warrant wood fibres boards without a membrane where there might be batty monsters because of the urine. But if TLX isn’t suitable- what the hell do I cover the roof in?

 

Has anyone done a retrofit solution other than bitumen felt?

[BadgerBodger]

Out of curiosity why the aversion to felt on top. The celotex is vapour impermeable anyway so what’s the difference? Or am I being ignorant? 

[Wil]

Frankly, I’d prefer the whole lot to be breathable- woodtherm or similar for insulation then a breather membrane over. My experience of bitumen felt is disintegrating membrane (both our previous house and this one) where it has become brittle and just breaks up.

[sgt_woulds]

I work for one of the woodfibre insulation manufacturers we’ve had a couple of similar questions regarding bats in the last few months – hopefully, this means there is an uptick in bat population, but it is awkward to specify a suitable breathable build-up.

 

Below I have copied the relevant parts of some previous conversations FYI:

 

 

Firstly, unlike spun fibre insulation, such as fibreglass or Rockwool, woodfibre insulation does not pose a direct threat to bats due to entanglement.  However, speaking as an ex-roofer - and having seen what guano can do to structural elements, membranes, insulation and electrical cables - I’d recommend keeping them separate wherever practicable. 

 

There is a fundamental contradiction when considering the building fabric's breathability and ensuring a safe environment for bats. Breathability is critical for the building fabric, and the only way to achieve this in a risk-free scenario is to use an external layer that ensures water vapour can escape. So a breather membrane or vapour open board.

 

However, the risks associated with long-term exposure to guano should not be underestimated. In volume, it can also pose a significant risk to the wood fibre and the structural timber. The use of a bituminous felt is therefore the recommended approach when roofing to ensure no potential trapping of the bats and to protect the structure.

 

Of course, bituminous felt is non-breathable and hence not ideal for the building fabric. Creating a fully vented cavity below the felt can solve the breathability issues but you also need to vent this at the eaves, and ridge which is not straightforward when trying to ensure that bats can’t access this ventilation space.

 

You could use TLX ‘Bat Safe’ breathable membrane as an alternative to Bitumen F1, but I’d be guided by the bat experts on this.  I remember speaking to an ecologist on a job 15-20 years ago and they were critical of the testing procedures used to validate the membranes.  This is not a fault of TLX, more that it is hard to test without using real bats! 

 

Hopefully, they’ve resolved any issues by now and I'd hope that they have some long-term monitoring data to confirm it's real world performance. 

 

You certainly shouldn’t use a standard breather membrane -I’ve stripped it off a roof where it was killing bats that got tangled in the threads and it was a sad sight.  

 

I’d still rather use the felt though.  My gut feeling is it will stand up to the acid in the droppings better, but I only have personal experience to go on.  I have, (unfortunately) dealt with many pigeon infestations where good old F1 felt stood up well to the muck, but on the job I had with bats and the breather membrane you could poke your finger through the membrane where the guano was removed.

 

 

Going down the ventilated void route would sort breathability, but reduce available insulation depth.  In addition, we always recommend a secondary water removal layer below felt as it can degrade over time, which makes the build-up more complicated. 

 

A more holistic approach may be to consider a non-vented build-up which allows breathability back to the inside.  In this scenario, external ventilation is not critical, but overall performance should always be justified by a long-term hygrothermal analysis of the fabric, (via software such as WUFI which also considers external exposure, rain, shading, occupation and use, etc on a project-specific basis).

 

As an example of a vapour closed approach, please see the build-up below, which may be an option with suitable analysis.  This uses a woodfibre sarking board externally and woodfibre flex insulation between the rafters:

 

 

 

In this simplified example, the U-value, based on an existing 120mm rafter, is 0.26W/m2K.  You will see that there is condensation shown by the software, (U-bakus)  - but, with full WUFI analysis, this may well be at a level that is not critical. 

 

SIGA, (and other manufacturers who produce moisture vapour-variable control membranes) will undertake a WUFI assessment if their membrane is used, so we have shown their Majrex 200 and would recommend this as an alternative approach which addresses some of the factors discussed above.
 

[not shown in the diagram is the lime or clay plaster on the woodwool panels]

 

Felt does degrade over time, (so do breather membranes) but in my experience, this is exacerbated by their own weight stretching the reinforcing fibres over time and under summer heat.  Fully supported over a sarking board this should be less of an issue.  Even if the felt does fail in 50-odd years time, then, (if you choose the right product) the woodfibre sarking can act as an additional weatherproofing layer with its hydrophobic surface coating.

 

Using an external sarking board and counter battens as in this example will only raise the overall roof by 60mm which really only shows at the gable ends, and can again be ameliorated with architectural detailing.  A conservation officer probably wouldn't even notice it on the finished roof from the ground unless you pointed it out to them.

 

A practicable modification to the existing roof profile that allows for lowering CO2 emissions, protects the building structure, and allows a safe habitat for wildlife it is a compelling argument to use with planning and conservation officers, and ensures the building will be fit for use for many more years with minimal visual difference.  Surely this is all they can ask for.

 

In terms of ultimate U-values, this isn't the be-all and end-all in terms of thermal comfort, and building regs with older properties.   For existing elements in existing buildings, Part L of the Building regs defines a threshold value of 0.35W/m2K for Roofs in certain conditions where it's not practical to achieve the modern requirements.   Worth discussing with your BCO; for an older building, most BCOs are now sympathetic to the argument that breathability is more important than the insulation value.

 

Woodfibre will also provide more decrement delay than unnatural insulations; summer heat protection is probably just as important these days as keeping warm in the short winter months.

 

I suggest speaking to advisors at:

 

Home | spab.org.uk and

Historic England - Championing England's heritage | Historic England 

 

as they have experience with upgrading the thermal performance of old buildings whilst maintaining their architectural features and may have some case studies you can use.

 

 

 

Can you provide links to the information about Batsafe membrane being unsafe for bats?  I can only find historic 'concerns'.

 

 

 

 

[Wil]

@sgt_woulds What an excellent and in-depth response, thank you.

 

I take it the 35mm in your build up above is the wood fibre sarking board? The label appears to be missing.

 

What stops condensation forming on the internal side of the felt membrane in your example above? This was an issue in my old loft when I pulled back the glass fibre insulation that had been stuffed between the rafters (badly)? I guess I need to understand the WUFI calculations properly. And my rafters are only 100mm to play with. Given the felt barrier, a cheaper way could be to use celotex over the rafters in place of the sarking boards- making the whole roof warmer? I’d happily have open rafters inside if it made things better!

 

Sorry to answer with a whole raft of questions, I’m just fighting with the concept of mixing breatheable and non-breatheable materials on the roof and the horror stories you read on condensation. 

 

My only real references to TLX not being suitable are above in the thread, but I had read it elsewhere too. No recent or real worked experience, so if people are now happy that TLX isn’t murdering the flying squeakers, then all good and I’ll have to dip in for the expensive stuff! £16/m2 🤦

 

 

[sgt_woulds]

TLX has been on the market for decades now - I'd be very surprised if it was not up to the job.

 

When I spoke to the bat expert on our roof replacement job, TLX was still fairly new and the manufacturer had only just come up with an approved testing method to confirm performance. 

 

Her objection was that it hadn't been proven safe in the real world; obviously, they couldn't test it on real bats and used a spinning apparatus with lots of little hooks (like a wool carding board) to simulate bat claws scrabbling against the fibres.  I'm not quite sure what she actually expected them to do to prove it!

 

I'm sure TLX must have that real-world evidence by now, but if it is still killing bats I'm sure there would be more horror stories on the interwebs.

 

 

As to your other questions:

 

Yes, 35mm woodfibre sarking - labels removed as this is not the place for company adverts and I'm not answering 'officially'...

 

'Simple' U-value calculators such as UBAKUS will always show a moisture risk as they can't accurately model the sorbative properties of natural insulation.  The fact is, there will be some moisture forming on the very outside layer of the insulation, and it is imperative when you design for a moisture-restricted system, that you allow for a path. to transport it back inside the building when conditions allow. To be effective, this drying path, (driven by sorption and breathability) must remove more moisture long-term than it accumulates over short periods.  The only way to confirm if this will work in each situation is to have a WUFI assessment interpreted by an experienced assessor. 

 

We don't generally advise vapour-restricted constructions with natural materials and It won't work in all situations - but we should never let perfect get in the way of good enough! 

If WUFI confirms that the moisture load is not excessive long-term, then it is a solution that can be weighed up in this particularly tricky circumstance.

 

I'm not against combining natural and unnatural materials, but again this should be modelled carefully;  I'd be driven by the WUFI expert's advice on this.  Moisture will get past gaps in the PIR and condense into water between the PIR and felt.  As PIR is not sorbative, this moisture will not easily transport back inside and will build up.  Freeze/thaw at this junction could cause damage to the felt and PIR.

 

Another thing is that PIR insulation shrinks - especially when subjected to a high-heat location under tiles - and this would increase moisture issues and reduce thermal performance.

 

Open rafters are not a solution, you need a moisture vapour-variable membrane, that will restrict moisture entering the insulation but still allow it to return inside when conditions allow.

 

Most moisture issues are caused by poor airtightness rather than the type of insulation material.  It is, (theoretically) possible to create a fully airtight roof insulated with unnatural materials but it is not likely in reality.  This is where the vapour open and sorbative, (active moisture movement) of natural materials wins out - but it still requires very careful taping and sealing of the

V-VCL to make it work.  This will also make your building more airtight which is just as important as increasing the U-value.

 

I'd fit this membrane myself - I'd never trust the average builder to take the time to do it properly.

[Wil]

@sgt_woulds Another excellent and in-depth response, thank you again!

 

Our Batman appears to be giving us the option of TLX or Bitumen and nothing else. So I suppose those are my options and he must consider it safe!

 

Then it’s down to the insulation options I use- the builder has ‘allowed for’ his standard 75 over 75 between of PIR because that's what he does to meet regs. Nothing wrong with that on new build. I had specifically got planning to raise the roof lines so I could go warm roof, but without much more than a simplistic ‘warm roof will keep all moisture issues away’. Could I do your whole buildup on the outside of the rafters? Rafters, VCL, insulation, tlx, tiles? It would make some interesting details at roof intersections and gables, but I think that’s ok.

 

Happy to discuss in PM if it’s easier to mention brand names/ buildups, will not take as pressure to buy 🙂

 

 

[sgt_woulds]

It may be possible to use all insulation above the rafters - with a WUFI assessment to confirm that it works.  I cannot stress that enough.

 

Also, using woodfibre above the rafters would require a significant depth of insulation to achieve similar U-values to the example shown above - you would be using dense insulation boards throughout and these do not provide as good a U-value as the flexible woodfibre used between the rafters.

 

Shown below is a build-up with U-value of 0.248 W/m2K:

 

 

 

Here, the 18mm OSB3 is used without a VCL membrane and a UDB breathable membrane is used above the insulation.  Ubakus doesn't have the TLX Batsafe listed, but this should provide a similar performance. 

 

Two layers of woodfibre are shown, 100mm of better U-value, and a layer of 40mm which has a hydrophobic coating to provide additional weatherproofing.  In this case, the breather membrane is used as protection from the bats, otherwise it would not be required.

 

If you can find the correct quality of OSB3, (unfortunately, not easy in the UK) it can be taped and sealed to provide both airtightness and vapour control.  You could also use a VCL over the ply if required.

 

 

Points to consider:

 

• Fixing Length  –  with this thickness of build-up the fixings would be a minimum of 220mm long.  The fixing process needs to be exact to make sure that the fixing penetrates the centre of the supporting rafters. This can be difficult to achieve consistently with such long lengths.  If a lower U-value is required then the overall build-up increases as does the screw length.
•  
• Counter batten size –  the counter batten and screw hold all the insulation in place and need to be designed to withstand any wind & snow loads and carry the weight of the external finishes.  The counter batten width needs to be sufficient so that when the fixings pull into the structural frame, the batten doesn’t pull into the insulation layer; the woodfibre is relatively dense but this needs to be accounted for.  Hence the fixing manufacturer, (e.g. HECO Topix Screws) must design a fixing methodology to consider all the following factors – wind load, snow load, exposure, insulation type, batten size etc.

 

The same build-up using F1 felt and a V-VCL membrane will show moisture issues in Ubakus, but again, if you have it assessed by a WUFI expert you may find this is within acceptable levels.  

 

I suggest speaking to 'Mike Wye'  or  'Back to Earth' as they have more real-world experience in their technical teams and will be able to advise accordingly.