This year has been really bad for it with us. We have 10 poultry houses - garden shed, coops, arks a variety of designs. None has felt roofs,but all are wooden. We build our own and now use ply as T&G was offering too many hiding places. All perches, nest boxes etc come out, and i clean the birds about once a fornight, unless there is a mite problem.
Ive got it really bad in my Buff Orp house. A bit of litter fell outand under it was a seething mass! Iemptied it and it was like a horrormovie...a seething mass of movement.....
Tomorrow afternoonIm cleaning, spraying (yet again) and eprimexing the birds...
I think its just keep at it.....for me Jeyes works well internally with creosote externally. Its just a chore having to continually do it. If I could get big bits of UPVC Id use this,bolted together.