Having got my "roof feet" in June (and having to wait until last week to know it was a success) the next project up there looks like being one to take the output of the bathroom and cloakroom extractor fans, and try and pipe it directly through a modified roof tile that it seems you can get these days.
Currently they both have to pull through a 180-degree bend, which reduces the efficiency quite a bit. They also have to go into pain-in-the-arse-to- reach soffit vents which then point *down*.
So the thinking is to change the fans orientation to vertical, and have one pipe in - straight - and the other out - straight until it goes into the roof tile.
It's a concrete tiled roof, if it matters. I am starting to develop an aversion to anything sold as "universal", so is it best to get a specific vent for the tiles on my roof (Redland Stonewold II) ?
And, of course, any "gotchas".