Venting bathroom exhaust fans into soffit

This is a rough cross section side view of the front of my house. It's amazing the crappy drawings one can make with MSPaint. :-)
http://members.rogers.com/kevinck/house/house.jpg
The downstairs bathroom is the issue. Every other fan (bathrooms, dryer, kitchen, etc) on the house has a corresponding vent except this one. There is a vent directly above the bathroom fan so we assume that's what it is for but it doesn't ever get used. The bathroom fan turns on, and it even sucks air, but none ever comes out of that vent. It was something we put on the list of things we wanted the builder would fix when they came back a year after construction. All the nailpops and whatnot were fixed just fine but the guy they had doing this told us that the downstairs bathroom fan vents into the soffit and that's all it's supposed to do. I asked "Then why is there a vent on the roof?" His reply "I dunno, but that fan looks like it was installed to vent into the soffit and it's doing that just fine."
That small section of roof has no attic type access. There is no way for us to get in there at all. I took the fan out but there's a metal bracket which i think i'd have to rip right out of the drywall if i wanted to get a better view up there. I didn't do that. And there are no other vents of any sort in that small section of roof.
Questions: Is this venting of a powder room directly into the soffit a problem or a regular practice? Since there's no shower or bathtub to produce excess moisture, maybe it's not a problem.
Why did the builder put a flappy vent right above the fan and never use it? My assumption was that they meant to connect the fan to the vent and forgot, but my builder is respectable and so seemed the repair guy. I don't automatically assume he's giving me a line to avoid doing work.
The only other thing it could be is just a way for that small roof area to breathe to the outside air. But if that was the case i would have expected just a roof air vent like the ones that are up on the attic roof (not in my picture).
Kevin
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Safely, produce some smoke, vent it, and see where it goes. (Maybe a red hot skillet and some wetted mesquite chips?)

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Nice diagram. If it were my house, I would leave it as-is because there's no shower downstairs. If you are so concerned, poke a simi-rigid hose such as corrugated plastic drain pipe into the roof such that the top end is a few inches from the vent, and glue it or nail it or do whatever the heck is required to make it stay in place, and feed the fan air into it, and that will be 97% better than no pipe at all. I have done something similar. -B, handyman

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Yea, he does not want to fix it right. Let him fix it right, it's your home.
Will it work. Well I see two possible problems. First if there is not a backdraft valve at the fan and it was designed to use on at the exhaust, you will get cold air coming in. Second, if you or someone wants to use that bath in a way that generates a lot of moisture, then you will have a problem.
I would expect them to do it right.
I don't know about you personally, but some atheist are atheist because they can't accept the concept of a being higher than they are. It is an ego thing.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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Kevin, If I read your diagram correctly, the fan is venting into the porch attic. It may not be venting the amount of moisture a shower would provide, but when it is cold out side the warm air may well reach its dew point in that space. The result is the same as a cool glass on a summer day - condensation.
The flapper on the roof makes no sense to me if it is not connected to a duct.
Tom Baker
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Kevin,
The "flappy" vent is correctly termed a barometric vent. When the pressure inside the soffit space reaches a certain pressure, the vent will open and releive the pressure. What may be happening is the envelope surrounding the soffit space is not sealed properly, thus infiltrating or exfiltating the air. If the air is exfiltrating, it is a good thing because the exhaust air which is heated in the winter and cooled in the summer is helping to provide a makeshift air barrier in the soffit space, and as stated earlier, there shouldn't be any added moisture to the space. If however, the soffit space is infiltating air, you may eventually have a mold problem from moisture entering the space. Either way, the exhaust fan is only helping the situation by pressurizing the soffit space somewhat.
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