by Jim Schiller, Schiller Roofing. Reprinted from Western Roofing magazine, March/April 1996. Problems with Condensation in the Attic can be a Roofing Contractor's Nightmare     I doubt if there is a roofer in the country who has not come up against a condensation condition. The first thing he knows is when he gets a call from a customer complaining about "His" leaking roof. These calls are usually accompanied by some reference to some friend or relative who's a lawyer and "Do you guarantee your work?". My customer called a few days ago with a complaint that the new cedar shake roof that I installed on his bathroom addition was leaking. I don't take these calls lightly, and as a matter of fact it upsets my ego to even think that I had made a mistake bad enough to cause a leak in a brand new roof. I made an appointment to be at the owners house at 9:30 the next morning and was fully prepared to remedy the trouble whatever the cause. Sure enough he was right. There was water dripping through a ceiling fan in his new bathroom and it was raining outside. It looked like a roof leak and I was embarrassed.     I climbed the ladder and carefully examined every square inch of the area. Everything looked okay. My side laps were correct. There were no split shakes and no exposed nails. No sign of anything that might cause a leak. Nothing!     Next step the attic. After emptying my pockets of anything that might fall out, I crawled some 70' through the trusses and 12" insulation being careful to step on the ceiling joists to get to the area in question. Whoa!! There was water all right, lots of it. Water dripping off the entire under surface of the roof and running down the aluminum flex pipe and into the ceiling fan. Everything was wet, even the gable end wall. Luckily I had a customer who was willing to follow me into the attic so he could see for himself, but he was entirely in the dark about how the water got there. This was a classic case of condensation and I was again amazed ar.     This house had all the "No no's" and was a perfect candidate for a severe case of condensation. I've seen hundreds of them in my 42 years as a roofer and have been blamed for many roof leaks that never were.     In 1956 I was probably the first contractor in Oregon to ever install a polyethylene vapor barrier under a house. I didn't know much about it then. I only knew that it worked. Windows stopped sweating, paint stopped pealing, toilet bowls quit dripping, mildew dried up in the closets and fuel bills went down. Later studies proved that a really effective job needed both attic ventilation and foundation ventilation along with the vapor barrier.     I've been thrown out of more houses than most people have even been in trying to inform people about condensation but 40 years of effort has produced very little understanding of the subject. Even building inspectors don't fully understand, they just enforce the code that says they have to use a vapor barrier and install so much ventilation per square foot. I've mellowed a bit through the years and changed my tactics. Instead of talking about humidity and vapor transmission rates and "R" factors and air convection and dew point, I just tell them "Don't try to understand it, just do three things: install a good polyethylene plastic cover on the ground under your house; open your foundation vents and leave them open; and add more attic ventilation.     The whole point of this is for all roofers to beware, be informed, study it, understand it, learn it, know it, suspect it. Be ready to defend yourself with gut knowledge on the subject of condensation because chances are you are going to be blamed for a roof leak that really isn't, and possibly end up in court.     The following paragraphs are a simplified condensed treatment on the subject of condensation plus a few helpful hints for the roofer who is willing to do something about it.     Forty years of agonizing over the subject of condensation inside a building, whether it’s a factory or just a bathroom has produced a vast amount of information coupled with hundreds of case histories. Trying to find a common denominator and in some way simplify the subject has been a lifelong endeavor.     Everything from a simple sweating window to an entire hospital's flat roof with blisters the size of row boats to entire rafters in an attic rotted to the point that the roof caved in, have shown ample evidence of condensation. Mildew in closets, dry rotted foundations, peeling paint, high fuel bills, hot stagnant upstairs bedrooms in the summer and cold clammy rooms and damp smelly air are other symptoms of condensation.     Condensation has no respect for winter or summer. Even though most problems occur during the winter heating season. There are times when a vaulted ceiling in a home will drip water during 80( temperatures in August. Daily changes in outdoor temperatures and relative humidity also have varying effects on indoor condensation there by producing day-to-day variations. Now that we've identified the problem lets get down to the cure. Find the source of the moisture. It can be anything from an indoor swimming pool to a flooded basement. But most often just bare ground in the crawl space under house. Such bare ground may look dry and innocent on the surface but will produce as much as 20 gallons of water vapor per 1,000 square feet within a single day. Water vapor is what happens to any water when it evaporates and becomes part of the air. The most effective and inexpensive method of stopping this evaporation is to install a .006 mil sheet of polyethylene onto the entire ground surface. Such a ground cover should be complete and cover every square inch possible. Seven inch gutter spikes. with pieces of roofing material fashioned into large thumb tacks are a cheap and effective way to pin it down. If there's water standing it must be ditched and drained away or install an automatic sump pump after ditching to a low spot.     Proper ventilation in the foundation. Most houses have adequate foundation vents but most of them have been closed off for one reason or another, mainly on the false belief that they're saving heat by closing them. They should be left open year around with the exception that when temperatures get cold enough to freeze water pipes under the house, and even then leave them partially open, especially in the outside corners. Properly functioning foundation vents are the natural intake openings for fresh air into a house.     The attic. If there is an attic, F.H.A has a rule of thumb for attic ventilation. One square foot open for each 300 square feet of basic floor space. Second story floors don't count, only the first floor. Half of affix ventilation is for intake vents in the soffits and half for exhaust vents in the roof or gable ends. A vaulted or cathedral ceiling must have a continuous ridge vent and continuous soffit vents on both sides because each set of rafters create a separate dead air space. Manufactured homes have a special problem in that they usually have two attics separated at the marriage line so both must be ventilated.     Stand back and admire your work. The long term benefits come in the form of comfort and a healthier indoor environment besides saving the house from deteriorating dry rot and other damage. Back to Economy Roofing's FYI