Agree. You can imagine what's like the like of months if not years of constant suction into ceiling space. This is more so if you have hot water, as the moisture is the starting ground for mould development.

In reality although an ideal, sometimes it's cumbersome/troublesome because toilets however have no ventilation outside due to renovation claiming backyard hence closing off vent-out spaces now reclaimed by renovated area/rooms. I've seen them mounting ceiling vent into ceiling space nia. Mine is such but I don't hv plaster ceiling but rely on fixed louvre window veniting into dry area. Installing an extractor fan on the backyard wall somewhat though not ideally deals with the air/odor wafting out away from the dry area.

In that scenario, for health reasons, it is proper to duct it outwards with ducted ceiling vents that runs out to the wall of the backyard.

For condo and apartment toilets with casement window of leaf opening up-down type, just install glass mounted suction fan.

Same for landed with the same window configuration or else just bore through masonry with exhaust fans. Some like KDK/Panasonic has one model, En (4"/10cm) and Zen (6"/15cm) extractors which is for areas that have very little overhang from roof. This series have an accessory hood that elbow downwards on the exterior to prevent rain infiltration.

Edit: One practical matter is unless you hv additional switch point for extractor fan, what I did was to branch it off the toilet light point. Hence can leave fan on while light can turn off. Otherwise in the long run cost $$$ to vent cos light must still run. The other alternative is to install pull switch for light with the obvious drawback of having to grope for it in the dark to turn it on.

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Added on July 27, 2012, 4:34 pm
Without outside roof, venting into ceiling space esp if ground floor toilet causes back pressure on the fan. The miniscule dirt and mold spores could be blown out due to backpressure.

Venting into roof space should be ducted with a roof vent/duct otherwise moisture build up inside here could affect lifespan woodwork holding up roof.

i installed ceiling mount exhaust fan. why do i get foul smell whenever i turn on the exhaust fan? there is no odor when it's switched off, only smell the odor (smell like sewer) when it is on.

i opened the ceiling manhole, no smell detected.
it's not coming from the drain floor trap either.

what else could it be ?

Yeah, partially opened. you are suggesting that the smell is from outside? My toilet is at second storey, if the fan can attract and suck the foul smell from outside, it's really unbelievable. Later i try shut the window and test again

No improvement after shutting windows.

I will check out those areas you mentioned. Hopefully can solve it soon, thanks a lot

I didn't open the window , just exhaust fan
ya i on my light too, personally i love to switch on the light to make toilet more bright , actually day time from 8.30-6pm also at office , very less use the toilet at day time except friday only (terengganu friday off day)  , i using LED downlight very save energy no worry 
brother , it will dry up if the sun heat up , but how about raining day?? Who gonna help u heat up the ceiling ?

You don't on your aircond to sleep?

hi all,

i have a exhaust fan mounted on my toilet window just like the above. However, my toilet still feels very "wet" and already have mold on my plaster ceiling although I just move in 8 months ago.

Contractor previously told me my condo is quite old (14 years) and has house sweat. Whatever bullcrap that is. I even have molds on my PVC in the masterbedroom and shirts which I havent worn for a long time. How do I get rid of molds?

Thanks, I will look into the machines, but they're not cheap as well
Already have exhaust fan. Will try hippo.
Not sure if it is leak because the mold is quite evenly spread across the plaster ceiling. My toilet window is only about 3ft (h) x 1.5ft (w).
Plasma or ionizer doesnt help right? It says prevent mold from forming. Not sure.

Hm weird, i open it as well. Let me try on the exhaust fan longer.