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Wednesday, April 27, 2011

Why Snow Came in Your Vent Ridge

When the dry snow hit McKinney, Prosper, and Denton two years ago, a lot of homeowners had a lot of snow penetrate their attics. The roofers instinctively blamed the manufacturer. My wholesaler reps were calling me to ask why this was happening. Wasn't happening to my customers. Not one. But the neighbors had problems so our customers called us to inspect their attics. We told them it wouldn't happen to them because we had mono-altitude exhaust vents and balanced soffit vents. They had forgotten the pitch so we had to go through it all over again. We also pointed out that they didn't have ice daming problems because of their roof/attic ventilation system.

Most roofers apply the most basic of gas laws when they install exhaust vents. They only relieve pressure. The concept was first outlined described in Boyle's Law, circa 1662, in that at a constant temperature the volume and pressure of a gas is constant. Later researches found  the relationship between the volume of gas and pressure is affected by temperature. By the 18th century the gas laws grew more comprehensive, culminating in the Ideal Gas Law.

If this is the only application of physics your roofer does, he is draining you financially, physically, and emotionally. Vented only roofs wear out everything. The roofing fails early, the warranty is void, your kid's doctor reaches a higher tax bracket, the utility company executive gets a bonus, the painter is employed, your insulation mats, the air conditioning repairman buys a new truck, and later the manufacturer expands their facilities. If you believe in climate change, you sin when you use lo-tech roofers.  

What most roofers do is 16th to 18th century technology. Well trained roofers use fluid dynamics to ventilate. Air comes in the soffits and out the mono-altitude exhaust, creating a giant Venturi Tube. Any interference between the top line exhausts and intake vents and the system shuts down like a soda straw with a hole in it. The classical example is the "Chimney Effect" but we prefer the straw because a chimney heats from the bottom but a straw is used to pull just like the sun's energy heating the attic air, speeding up the molecules. Excited air molecules move up. Slower ones don't.

When you first cut a hole in a non-vented roof, the rush of air will blow your hat off, then slow down. If their are soffit vents the rush will continue and only decrease as the temperature drops. As the hot air leaves, ambient air comes in soffits. With the removal of heat and humidity from your organic material infested attic, the spores die and your doctor needs to sell his car. The kids asthma goes away. The air condition doesn't run as often.

If you over exhaust and do not increase the soffit intake to match and you have a modern home with house wrap and energy efficient window, a new bogyman arrives. Radon gas and his other under-worldly buddies come seeping up.  Your water might boil faster but your home will smell like sewer gas. You can clean all you want but until you find a professional roofer, your house might stink.

But your lower vent ridge might also become an intake vent, sucking in rain and snow.

Sorry for the lack of clarity but I've been interrupted about 50 times this morning and can't keep a clear thought.

Jon Alan Wright
Jon Wright Roofing, Siding, and Windows
1915 Peters Rd., Suite 310
Irving, TX 75061
972.251.1818 Office
214.718.3748 Cell
972.554.8090 Fax
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