Hanging light voiles and lace at the windows to keep the big summer bugs out (yes WBFM, there IS a reason why I buy this stuff!) is ESSENTIAL unless you enjoy fighting off winged things whilst you eat, sleep or just try to read quietly
Long term followers will have read about our historical and sometimes hysterical attempts to beat the little blighters. See:- https://coteetcampagne.wordpress.com/2013/05/14/the-big-wormy-beam/
Let me just raise a Very Important Fact right here, French houses have a very high proportion of wood in their construction. In some it is the main material. You need to look at this issue at the earliest possible stage of your project.
Damp & rot also need addressing STRAIGHT AWAY; Forget the decorative flourishes, the gorgeous furniture or the tempting paint charts for now. Of course I could not resist “considering” any of those.
After some battles with our 18thc cottage in the UK , in which tenants allowed rot organisms to flourish, this was an early preoccupation when we bought the French house (also tenanted on occasion before our time). After years of benign and active neglect, a bargain property will have some infestation to contend with. It makes sense to deal with this whilst the place is being stripped back for major work
We decided that it would be sensible to strip everything back and let the place breathe to start with. This shows up any serious damp (as opposed to condensation) issues.
Damp/rot-We were fortunate- apart from the obvious (missing/slipped roof tiles) doors not shutting properly, effluorescence under stairs (cured by opening up a doorway in a dank corner) our issues were obvious and easy to fix, if not cheap.
Wood boring beetles- Woodworm was rife in the garage (see thebigwormybeam link above) but at least we didn’t have termites ( blessedly a standard French house purchase check in the South !) Mostly inactive now, apart from a popular plank on the salon floor (?!), the ancient joists had been augmented and supported in the early 20thC and the beam that holds the house up is still rock solid within, though it looks alarming-Below–
Fortunately, when we exposed what we think is a chestnut beam on the top floor, it was absolutely sound. Spiders don’t like it either (they just lay their eggs elsewhere when we aren’t there!) We treated by soaking every bit of exposed wood in the house with Xylophene
Effective against the “larves xylophages -Lyctus, Vrillettes, Capricornes”, they sound so cute in French.
Every new bit of wood we expose or add in, including wooden furniture, trims etc is also treated to future proof us.
I have recently read an expat article stating with confidence, that exposing beetle infested wood to light and air will fix any problem. I’m sorry, it won’t, modern chemicals are required and they are not, by their nature “safe”, so wear masks and gloves.
The “old ” remedies included painting furniture and floors to deter these little critters was, for many centuries, the ONLY defense (hence painted furniture and floors!) but it was all that was available back then. Get real and buy something that works.