Why is this bag of water hanging in the attic and should you have one?
Short answer: No. The attic space is outside the heated area of the home and such water will freeze, eventually break the plastic and soak the building materials and leak into the home interior. So why is it here?
Here’s the bigger picture;… it’s a real effort to do it the wrong way.
The blue arrows (1 & 2) are the start and direction of the exhausts from two bathrooms. Instead of going straight up and out through the roof, the ducts are bent downward to exit (arrows 3 & 4) at the soffits. That is the basic error.
Amateurs often are uninformed about correct methods to open and flash an exit through the roofing, so like here, they get quite inventive and do a lot of work to ‘solve’ their problem without cutting the roof. ‘Duct tape’ is not a building product any more than it is a car repair product so it’s presence is a dead give away.
This ‘thinker’ must have heard about condensation but does not understand the use of vapour barrier. Only incomming ducts are insulated. Exhaust ducts are not and vapour barrier on the cold side of insulation is wrong and in this case is what gave us the ‘bag ‘ of water.
Note the water colour. Not the pristine clear colour of condensed water is it. This is an indicator of another condition as is the photo below; … stains and ‘lint’ on the ceiling grills are problem indicators. Yes we’re talking mold in the ducts.
Duct runs going latterally or horizontally just allow condenation to collect and along with all the house dust (skin cells etc.). Once the weather warms up you’ll have an explosion of mold growth because you’ve provided water, food and now heat.
The imperfections in the ceiling of the last photo is water damage. So if our ‘bag is holding water, is there a roof leak?
No, not a roof leak, just your old bath water back to haunt you.
Look at the circled areas in the last photo, and also in the second photo (an oval). This is mold stain on the roof sheathing from humidity that actually made it all the way outdoors but was then pulled back into the attic to do damage. Why does that happen?
Because the warm moist air is being released right into the intake grills of the roof venting (cooling) system, aka ‘the soffits’. Not much point in trying to get rid of it if you are only going to pull it back in again.
So all bathroom exhaust ducts that enter the attic must exit directly vertically and through the roof to the exterior. No latteral or horizontal runs. Insulation or vapour barrier has no place on attic ducts. You just want to blast the humidity out above the roof where it can do no harm. Exiting at the soffits is worse than useless.
So a bag of water in the attic is the sword of Damocles hanging overhead.
Original blog post on ActiveRain: Link to Blog Post