Hi,

I’ve recently purchased a flat (first time buyer; DIY noob) and I’m looking to do some renovations. The flat is on the top/3rd floor and was built in 1963. It’s got a flat roof.

My bathroom can get mouldy quite quickly; it doesn’t have any exterior ventilation except for a window which leads onto the communal corridor.

See this rough plan of my flat:

http://www.pbrophy.com/house/Floor_Plan_02.png

I think have a few options:

--- i) Ventilation fan onto communal corridor or via kitchen.
Putting a pipe which goes via the kitchen isn’t possible due to a roof beam getting in the way (the dashed line in the diagram), and fire regs rule out putting in a fan to the corridor.

--- ii) Ventilation fan via hall/bedroom (in red on my diagram).
I think the best route for my ventilation pipe would be out via my bedroom. I am intending to put fitted cupboards along the wall above my bed which would easily hide any pipe. Some questions:
1) Is extracting air over this distance viable?
2) What diameter hole/pipe would I need for this kind of extraction?
3) Would I need a special extractor fan to push the air that distance?
4) Is the pipe likely to get mouldy inside? Would It need to be removable for cleaning?
5) Could I theoretically put the pipe in the space between the ceiling and the roof above? Are my walls likely to go up into that space or is there a gap above the walls and the roof?

--- iii) Dehumidifier.
The other option is a dehumidifier. I’d quite like to put the dehumidifier in the bathroom cupboard (it’s huge, used to have a tank in it) and run a flexible pipe from the cupboard door into the dehumidifier. I’d then get the dehumidifier plumbed in so that I don’t have to worry about emptying it. Questions regarding that:
6) Would a dehumidifier remove water from the air fast enough for a bathroom?
7) Can anyone suggest a dehumidifier that could be installed in the cupboard and have a flexible pipe attached to it for the air intake?
8) Failing that, does anyone know of a small dehumidifier which I could mount on the wall above the end of my bath and have plumbed in? The dehumidifiers I’ve seen all tend to have large water tanks on the bottom which significantly adds to the bulk - and I don’t need that if I can plumb it in.

Thanks!