Preventative measures against possible rot or woodworm

[donmaico]

I am in the middle of having an extension done and noticed that after its flat rood was competed a foot long inch wide hole was left in the eaves of the existing buildings pitched roof where it meets a side wall.The builder overseeing the project, didnt seem concerned and said he had the matter in hand.Thing is its been 2-3 weeks like that and as the hole faces south west I am concerned about rain penetration and the possibility of rot or woodworm eventually affecting the whole rood area.I spoke to him today and he has put a temporary fill in until such time as he gets round to making a more permanent one.Thing is i am now wondering whether i should ask him to spray some Rentokil in the hole as a preventative measure or whether more drastic action is advisable such as getting inot the roof space and doing a thorough spray. That in itself would be a difficult as i live in a chalet bungalow and that part of the roof is behind an inbuilt cupboard.
Am i worrying unnecessarily or should I request further action be taken?
thanks