Well here goes, several years ago the code people I knew in Texas were allowing the exhaust from the bath to exhaust to the soffit and were accepting that as venting directly to the outside. Does anyone have anything with that in writing, or as I thought, if the soffit openings were to the size that would allow the same amount of air flow, is it acceptable to run the flex tube from the exhaust to the soffit? In Texas, is this considered directly to the outside as in IRC 303.3?
Thanks, Russ
I have read pro and con debates on that subject.
You need a fellow Texican to answer your question. Here, where there is no water in the air I would call it good. 
Any vent from the inside of the envelope will carry with it moisture and other particulate that will block and/or damage soffit vents. Soffit vents are used for drawing fresh air in and not for the exhaust of any air. Installing a vent in the soffit effectively reduces the required incoming air for attic ventilation. In addition, anything vented out of a soffit will most likely be drawn back into the attic as ventilation air is drawn back in.
Unfortunately the 2003 IRC did not make a concisely worded section concerning venting through soffits. If you read the IRC though there are several sections that deal with vents/venting near a soffit area and the intent is clear. Venting near enough to a soffit to allow the exhaust from the vent to enter the attic space is prohibited. For example the following section on venting. Although it discusses venting through a wall they did specify to keep the vent discharge in a location to prevent being drawn up into the soffit area.
The 2006 IRC did make a specific reference to it:
The following posts on the ICC BB are for your amusement/information:
Read the entire post:
http://www.iccsafe.org/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=4;t=008114#000002
Another:
http://www.iccsafe.org/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=4;t=007817#000000
If I recall correctly Uncle Bob is a BO here in Texas. Read his post:
http://www.iccsafe.org/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=4;t=007105#000000
Another:
http://www.iccsafe.org/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=000952#000000
it is understandable not to vent to a sofit for it will draw the vapors back into the attic. Here is a twist, would it be acceptable to have the vent tube terminate at the ridge vent inside the attic? Since the ridge vent is designed to pull air this allows the vapors to vent through the ridge.
The 2006 IRC prohibits it.
It doesn’t sound like good practice, anyway. The ones I have seen just screwed the side of the accordian plastic ducting to a vertical support in the attic. In time to come, the plastic deteriorates and ducting falls.
How many times have I see that.
Outdoors is outdoors, not near a vent for another purpose.
Builing codes are minumum standards, not necessarily good or better building practices. I say “It’s the least we let them get away with!!”. One older builder on the Fine Homebuilding MB’s had on all his posts “Bad builders build to code!”.