Hi, hoping this has probably been done many times and someone will have
a quick answer

I am just finishing off an extension which has left me with a
bathroom in the middle of the house with no external walls, so no
windows.

Can anyone suggest an extractor fan that would be suitable and upto the
job
of keeping the bathroom relatively dry from the steam.

Extractor will be vented through the roof

The other qestion is, are 18mm water resisitant Tongue & Cheek chipboard
panels
suitable for 1st flooring (especially in a shower room)

Thanks in advance for your responses

Gaffar