It happens all the time. We send someone out to a house, we look at the roof, and we discuss the ventilation situation. The homeowner scratches his or her head and says something like, “The other guy never mentioned any of that. Why is it so important?”
Let Me Count the Ways
Many contractors who look at a roof that needs to be replaced will skip a serious assessment of the ventilation situation. Instead, they measure, total up their squares, tout the magic properties and warranty of their shingle, and present a price to the customer. This is a mistake.
If you’re interested, you can go online and brush up on the physics of proper attic ventilation vs. none or inadequate ventilation. Simply put, an attic that is inadequately ventilated will diminish the lifespan of a roof. This can happen quickly or in slow motion, depending on climate and local weather conditions. But a professional roofer should be aware of this and be prepared to diagnose problems and suggest solutions. Doing so starts with an attic inspection. In the era of satellite photography, you don’t have to be on top of the roof to know what condition it’s in, but you do need to be underneath it—with a flashlight.
One big reason is mold. Nearly 100% of the time an attic inspection will tell you whether you have a rotted wood issue. No one likes surprises, and discovering discolored sheathing—that says mold—on installation day is unpleasant for you and the homeowner. When this happens, you have to stop the job and dispose of the mold, and the homeowner has to pay you to do that.
Alive and Breathing
The attic, that is. Various tests can determine if there’s ventilation and how adequate it is, but this one is foolproof. Stand in the attic on a bright, sunny day, and if you can see sunlight at the eaves, there’s ventilation. If you can’t, either there are no eaves, or the intake is blocked. Sometimes people working on the building will stuff the soffits with insulation, blocking air flow. This solves one problem but creates another. If insulation is choking off air intake, install baffles from the eaves up the wall and behind the insulation to allow air flow from the soffits.
If there are no soffits, due to the architectural design of the house, we use a product called FasciaFlow that attaches to the fascia board and is specifically designed for houses with no attic ventilation.
Air In and Air Out
Just because you see soffit vents from outside doesn't mean you can skip the inspection. The problem may be that air is coming in somewhere but has no place to exit once inside. Where it should leave, of course, is at the ridge. Sometimes people think that gable vents will do the job. But your best bet is a ridge vent. If there is none, close off the gable vents and cut back three-fourths of an inch on either side from the peak. We recommend a hard or a stick ridge vent as opposed to the rolled.
Unlike an active ventilation system that uses power fans, air that is drawn up through the soffits and that exits at the ridge is a passive ventilation system. Fans are good for hip roofs, where there isn't enough ridge to cut a ridge vent. But they are always burning power, so the passive ventilation system is the best way to go if appropriate to the building. Gravity vents also can do the trick, but you’ll need a bunch of them, and generally you’ll need to install them on the back of the house.
Not A Choice
Many manufacturers make a slide rule that enables roofers to determine the amount of ventilation appropriate to the attic space. Ignoring this could spell trouble for you and your customer. If the roof begins to wear out prematurely and the homeowner files a warranty claim, the exclusions in that warranty will probably include one stating that the warranty is void if the attic is not ventilated to industry standards. It’s just a matter of pulling the stairs down and going up in the attic. It’ll cost more—as much as a few thousand dollars—to get the attic ventilated properly. If you explain it, homeowners won’t blanch. I simply ell them I would be remiss in my duties if I didn't bring it to their attention. And I line item the price. Then the homeowner can sign off if he or she chooses not to address the ventilation issue. Ask me how many have signed off on that. Not one.