Hi there, I installed lap vents a couple of years ago and I am very pleased. I am now refurbing my bathroom and fitting a fan which it currently does not have. I would like to avoid cutting holes in the brickwork or cutting/replacing roof tiles so using a mechanical lapvent looks ideal solution however I have a concern. Assuming the roof is currently sound and no rainwater is getting under the tiles, the felt and battens should be dry. I am concerned however of introducing damp humid air under the tiles which presumably will condense and introduce water to the topside of the felt and perhaps more importantly run down the felt wetting the battens below, possably causing the battens to rot over time. Can you advise if this would possably be the case or am I simply worrying too much?