Hello all

I've been lurking for years and finally have an interesting project.Your help is sought.

It's a rectangular 550 mm wall solid stone built 110 sq m cottage in Wiltshire with bats in the attic.

Permission was granted in the teeth of the tree officer to extend it as an L shape ( a double pile was sought but encroached on two protected oaks so the wing doubles it in size hanging down on the eastern wall allowing good southern insolation to most windows)

The dream of making it EnerPHit was stymied when we realised that 200mm of floor insulation would have required £30,000 of underpinning due to the lack of foundation -so we applied to demolish the unlisted building and replace it exactly as before benefiting from the VAT newbuild concession.

And we nearly got away with it; on the eve of planning being granted, someone mentioned bats.

£5,000 worth of surveys ( that found five bats and their DNA) and six months delayed we have reverted to the original planning and are out of the ground with the extension - alas only 100 mm full fill thermal block cavity as we need to match the stone coursing of the undemolished cottage on the outside, but 200mm floor fill.

The cottage now has a reinforced concrete floor tray with a 125mm upturn allowing for 200mm there too and 125mm IWI. Triple glazing throughout to replace the Critalls.

My first question is what to do about the bat attic.: the licence to remove them will come in November by which time we will have completed the shell.

Do we strip the roof then and retile using a warm roof insulation or is it feasible to have an icy bat palace attic sitting on top of an insulated two floor box? The extension will be bat free and can have a warm roof.

Second question on pargeing - I'm aiming for 3Ac/hr to be realistic for MVHR . I need an IWI soultion to optimise the 125mm.

Many thanks

Ralph

Welcome.

'Optimising the 125mm' IWI could mean interstitial condensation if you are not careful. Take a read of BEIS' new-ish (and in my view under-publicised) IWI Best Practice Guidance: https://www.gov.uk/government/publications/retrofit-internal-wall-insulation-best-practice

Basically that guidance suggests a ventilated cavity behind any insulant which is not vapour-open (such as wood-fibre).

Many species of bats really like to live in crevices, 15-25mm is ideal. Gaps behind cladding, or above eaves soffits are good. They don't all prefer to live in big open spaces like a whole roof void space, unless there are crevice spaces within that void. You can get bat boxes to build into walls, or portion off a little corner of the eaves triangle Like this
https://www.bats.org.uk/our-work/buildings-planning-and-development/roost-replacement-and-enhancement/case-studies/conversion-of-redundant-barn-at-in-carmarthenshire

They are magical creatures to have around, you know you have done a good job of managing the garden food-chain if a bat chooses to live with you. There are a few in our bay window roof, it's great looking out of the window on summer evenings and seeing them heading out for the night. You might not currently feel well disposed after all your expense but you may yet come to love them!

Barn owls, on the other hand, would love to have use of your whole roof void...

here is the existing cottage from the north; the bats are in the attic

There is a new and expensive bat-friendly breather felt

https://roofin.co.uk/shop/tlx-bat-safe-bat-friendly-breathable-membrane/?gclid=CjwKCAjw3qGYBhBSEiwAcnTRLnw2uuTS-n_HExPsMd6Ra6YJEU7eBSX5T-sY9U192EpV7sgFWSdFaRoCF-UQAvD_BwE

https://www.bats.org.uk/our-work/buildings-planning-and-development/non-bitumen-coated-roofing-membranes

But, having a re-think, we are considering using 1F bituminous felt laid over the tops of the slating battens, no membranes below that, but a cross-ventilated cavity below the felt. Not unlike traditional Scottish practice. What would the team think about that? Wouldn't work with tiles, being hook-on and less proof, being not double-lap - but slates?? maybe plain tiles like this case as far as I can see??

<blockquote><cite>Posted By: WillInAberdeen</cite>
As I understand it, the bats are allowed access to the 1" gap between the tiles and the felt, which is just the size they like, and to the triangle bits at the eaves and ridge that you don't use. Unless your permission says different?, some species like more space? Then the attic space inside the felt is for the humans!

</blockquote>

Bats seem to be able to get through very small gaps if they want to. We have bats living in those triangular bits you mention, squeezing effortlessly through the spaces between the stones and woodwork high up under the gables.
From there they get through over the top of the walls into the airing cupboard and all the normally closed cupboards running the length of the house. The attic rooms are original, with a staircase running down from the upper landing to the first floor. We share the house amicably with the bats. Most of the time they restrict themselves to the shut off parts of the attic, but they occasionally come downstairs. We just open a window and they fly off outside and go back in again at the top.
They have no difficulty bypassing a cupboard door. Neither do the cats apparently. My wife opened the airing cupbard door this morning and found one asleep on a pile of bedding. It has obviously found a secret way through - perhaps under the floor boards.
Live and let live :)

Posted By: fostertom

Posted By: fostertomBut, having a re-think, we are considering using 1F bituminous felt laid over the tops of the slating battens, no membranes below that, but a cross-ventilated cavity below the felt. Not unlike traditional Scottish practice. What would the team think about that? Wouldn't work with tiles, being hook-on and less proof, being not double-lap - but slates?? maybe plain tiles like this case as far as I can see??

I'd love some comment on this. If it's safe traditionally in Scotland, should be good for top of Dartmoor?!

I thought traditional Scottish practice involved sarking boards? Not sure where the membrane goes? If you'd asked I would have said between the battens and counterbattens (assuming not under both) but that's purely a guess.

Interesting to see a bat thread as im shortly to be going through the same same problems..the extreme cost of the bat friendly membrane and the reluctance of the roofer to use bitumen felt.
I have also heard that there is bat friendly wood preservative -that is also extremely expensive.

Ill just have to cur corners on the insulation!

Thanks jonti - also the point is that Scottish slates all vary in length so, tho roughly sorted for long at the top, short at eaves (or the reverse) and graded in between, still ea slate is nailed at different c/cs hence the impossibility of arranging battens at suitable c/cs.