help -- frost in attic

[Calhoontuna]

Having a problem with frost in the attic localized directly over the bathroom. Think the culprit is the shower. We're talking large patches of frost on the roof decking and on the trusses. Sometimes it's so thick and white you can't see through it. Snows when you scratch it. When it melts it blackens the wood, making it look burnt.

Recently, crawled further into the attic and noticed that I had the same problem in the other shower, albeit on a much smaller scale. So, whatever is going on here is happening in both showers, though much more intensely on the one.

So I hired a guy to fix the problem. Over the years, he had installed a new light fixture in the shower, new octogonal vents on either side of the attics and soffit vents to boot, and these industrial quality fans that suck so well there's barely any fog left on the mirror when I get out of the shower. The moisture is jetted not into the attic, but directly outside through a port on the eaves.

Last weekend checked out the attic and there it was, same as it's always been. Anyone have any experience in this, especially in terms of bathrooms/showers?

What about these vapor barriers I keep hearing about? Is there any way to install a vapor barrier after the fact, or do you have to completely dismantle the bathroom? The contractor I hired keeps saying that the vapor barrier is fine, but I can't help but think something's wrong here. Maybe back in the Eighties when my house was built they were using a vapor barrier that has since then been proved ineffective. I don't know.

Any input appreciated. Pulling my hair out here, and am getting tired of throwing money at the same problem time and time again.

[LazyPup]

The problem may be plumbing vents.

The Uniform Plumbing Code requires all plumbing vents to go through the roof.

The International Residential Code requires all structures to have one "Main Vent" which must run undiminished in size and go through the roof. After that is acheived when auxillary vents are required they may terminate in the attic space. Although the code might permit terminating vents in the attic it is really a bad practice because it results in excessive moisture in the attic space such as you describe.

[Calhoontuna]

Thanks. I'll have to check that out.

[HayZee518]

Run the hot water in the shower and climb up into the attic space and take a look - see if you can see ANY "steam" rising over the shower. If you can, you don't have a vapor tight shower. you might try fiberglass batts between the ceiling joists to try to cut down on the leakage. as far as putting plastic up there, it may contain the moisture causing another problem of rotting wood. Another fix would be spray in foam insulation so that everything is sealed and the vapor can't get into the attic.