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Cooler Attics Prevail
For many homeowners, the attic is a neglected dumping ground. If you live in a house with an attic accessible by folding stairs or some other means, perhaps you use the space for storage. If your home has only a scuttle hatch hidden away in a closet, chances are you've rarely been in your attic or given it a second thought.
With summer almost here, however, it's a good time to start thinking about your attic, especially how it's vented and insulated. Proper attention to these factors can pay big dividends. The benefits include the prospect of lowering utility bills and boosting comfort, preventing ice dams and the resulting damage to ceilings and walls, making your roof last longer, and preventing health threats from mold and mildew. Unfortunately, there aren't many simple, universal recommendations for achieving these benefits, especially when it comes to ventilating an attic. There are some model building-code guidelines, but every house has unique features, including how it was built and the degree to which occupants use energy and create moisture. Moreover, the climate in which you live can make all the difference between a useful measure and a waste of money.
That's important, because manufacturers of products ranging from rooftop ventilators to radiant barriers and sheathing are making a pitch for your home-improvement dollar. To add to the confusion, there's disagreement among contractors and experts about the role of attic ventilation and how it's best achieved.
It's enough to make you want to shut that attic hatch and not look back. But there are some general principles and strategies that can help you sort through the ventilation requirements for your attic. At the least, these ideas should help you decide whether your home has a problem with attic ventilation and what if anything you should do about it.
Conditioned Air & Moisture
One principle that'ds widely accepted is that you want to prevent conditioned air and moisture generated in your home's living space from entering the attic. There's no advantage to having a warm attic in cold weather. In hot weather, you want to maintain a good thermal barrier between the attic and your living space, which may be air-conditioned. To keep heated and cooled air inside your home, insulate the ceiling. This really is rule number one. Make sure your ceiling is insulated appropriately for your climate.
Keeping moisture out of the attic is equally important, especially in cold climates where water vapor in warmed air rises and condenses in the cooler attic space. You've probably heard that a typical family home can generate a few gallons of water vapor every day, due to cooking, showers and other activities. Excess moisture can promote mold growth on roof sheathing.
In severe cases, condensation can cause water to drip on attic insulation and through the ceiling. Sometimes it can rot roof sheathing. But showers and cooking don't tend to be the main culprits, according to William Rose, a research architect with the Building Research Council at the University of Illinois in Urbana. In virtually every case of severe attic moisture that Rose has seen, the problem was traced back to a wet crawlspace under the house.
The attic moisture problem, Rose says, is really a crawlspace problem. Rose is one of the few construction experts in the country who has conducted long-term studies of attic ventilation and moisture movement in residential buildings. Using an eight-room test building at the university, he has collected data on the subject for the past 13 years. His research and time spent as a home inspector has led him to understand how damp air from wet crawlspaces and basements can migrate to the attic by following ductwork, plumbing and wiring. Those routes can be supplemented by lose-fitting attic hatches, wiring chases, dropped ceilings and recessed lighting.
The first goal, of course, is to figure out how to dry a wet crawlspace or basement. Beyond that, Rose advises all homeowners to seal penetrations that can carry moisture to the attic.
If you want to do one thing well, Rose says, do tight ceilings.A tight ceiling helps prevent most attic moisture problems in the first place. Ventilation alone won't always do the job, Rose says. So before you invest time and money in increased ventilation for your attic, make sure moisture migration from below is under control.
Determine the Problem
A tight ceiling is beneficial in any home. But it may not make economic sense for you to increase attic ventilation if your attic doesn't have any moisture problems to begin with. Short of feeling water dripping on your head, how do you know?
For homeowners in northern climates with a typical gable roof, Rose has some suggestions. (Note: These examinations should take place in the winter, when condensation is most likely.)
Go into your attic, or carefully stand on a ladder set through your hatch door. If you don't have lights in the attic, you'll need a droplight or some way to illuminate the space.
Look carefully at the roof sheathing. If parts of the wood have turned black, you may have a mold problem. Check for a pattern. Is the black area confined to the north side of the house? Is it only in a corner or in a spot where ductwork or a chimney enters the attic? These penetrations could be carrying moisture to the attic, and they should be sealed. Don't be alarmed by light frost on the sheathing, Rose says. That can occur in cold climates, even in well-ventilated attics.
In very cold weather, ice dams plague some northern homes. These buildups occur when snow on the roof melts and refreezes on the eaves. They are especially common on the north side of a house, where the sun can't melt all the snow off the roof. Severe ice dams can force melting water under the eaves and inside the house, soaking wallboard and ceilings. Attic ventilation can help prevent ice dams, but Rose stresses that the first priority is to limit heat loss through the ceiling. Good insulation is the key here. So is blocking gaps around ductwork or any penetration that allows heat to escape into the attic. Once again, tight, well-insulated ceilings can make all the difference. n
Tux Turkel is a freelance writer based in Yarmouth, Maine