Bat Cave – lockdown

Underneath our house are a couple of arched roof caves. When we first viewed the house with the agent immoblier there was a grey long eared bat hanging behind a ceiling light. We were assured that bats weren’t protected in France, but we’ve subsequently found out otherwise.

Since our initial visit, luckily for us, the bat has not been seen. There are no sign of bat droppings in the caves; unlike the loft with it’s broken window; so hopefully it was a fleeting visit.

When we first visited the house and caves there was clutter everywhere. The previous occupant spent several weeks clearing the house, with huge bonfires burning 12 hours a day, 5 days a week. The caves are now completely empty.

A couple decades ago; when I was first dating Mandy; I was an electronics engineer making tiny radio tags to track all types of animals from birds to elephants. One of our very first text exchanges went along the lines of ‘What you doing?… ‘Shaving a Bat’s neck. It’s giving me the evil eye!’…’huh? A live one?’
With radio tags, you had to use a nose hair trimmer to shave a tiny spot on the back of the bat’s head before using a tiny amount of super glue to attach the tag. After a couple days, the bat would shed it’s skin, along with the tag. The data could be used to track spread of diseases, bat populations or in this particular case see if bats were crossing from a small island (Brownsea Island) to the mainland to feed.

Having held dozens of bats of many species, I know even the largest looking bat can squeeze through the tiniest of gap. To stop the bats getting into the cave we’d need to make new doors. The bottoms are rotten and there are massive gaps all around. If you remade the doors using the current dimensions, at best in terms of wind and weather resistance the best description might be ‘gate’.

There are two huge air vents leading down into the caves that a bat could easily fly through without slowing.

You can buy some lovely looking reproduction cast iron grates. However, they aren’t the right size for the hole. Therefore we needed more than one. The problem is the vent hole is smaller than two. Therefore, the only answer was to butcher two into one.

We didn’t want to overly restrict the hole as the Creuse region is a high Radon gas area and keeping the caves cool has obvious advantages.

The first job was to measure the hole and then cut up the cast iron grates on the band saw.

The grate needed to be 410mm by 170mm. Where as each cast iron grate is 239mm long by 161mm tall. Simply joining two grates end to end would get a vent 478mm long. Therefore some careful cutting was needed.

I cut the vents into several pieces.

Vise clamps were then used to grip them together whilst I MIG welded them together.

Being cast iron, the metal wasn’t the best for welding. It was full of impurities. Luckily, this isn’t something structural and is basically for looks.

Once sanded back with a disc sander, the grate looked pretty good.

The grate will be sprayed matt gun metal black, with two coats of lacquer. It with then be concreted into the hole.

Added to the back of the grate will be some fine wire mesh to stop the cluster flies. The caves are never going to be air tight, but this will help block an easy access route.