Roof ventilation is a system of intake and exhaust that creates a flow of air. Effective attic ventilation provides year round benefits, creating cooler attics in the summer and drier attics in the winter. This protects against damage to materials and the structure, prevents ice damming, and helps to reduce energy consumption. Many cases of premature roof failure can be traced back to improper ventilation. A basic model of attic ventilation is 1-ft of ventilation per 150sq of attic floor space. This should ideally be balanced with 50% being intake and 50% exhaust. Ventilation deficiencies are the most common installation flaw that may void implied warranties.
Ice Damming
Ice build up may be directly related to roof ventilation among other contributing factors.
Ice dams form when warmth from within the home melts the bottom layer of snow on the roof, sending water trickling down to the edge. Upon crossing the "heat wall" or the area where heat is no longer escaping the structure, the water refreezes, cloging gutters and causing the water to pool. This may allow the water to spider under the shingles as it freezes, eventually finding its way into the home.
We can solve your Ice problems! Call today.
Shingles are intended to shed water, they are not waterproof!
More simply, under ice damming conditions, shingles are basically submerged in water. This is a condition that shingle manufactures do not necessarly warrant the performance of their products.
The installation of a bituminus waterproofing membrane generally referred to as "ice guard" is a must for northern installations.
This is now reflected in the 2006 Ohio Residential building Code.
When you take into consideration other variables such as complex or difficult roof designs, variations of insulation, and varying amounts of moisture production and retention inside the home. One may draw the conclusion that ventilation requirements will differ slightly from case to case. There are many instances of roof failure and mold contamination even when the roofer followed an engineers specifications.
During the design phase of the roof ventilation system, it is critical to consider all aspects of the roof and building design. Independent from the roof project, recommendations may be made to the owner regarding insulation and humidity control. At American Roofing, Inc., we refer to this as a ventilation assessment, and all of our installations will include some variation of this service.
Ventilation Details 
| COMMON VENTILATION MISTAKES |
| Lack of undereave or soffit ventilation. (Intake) |
| Mixing of exhaust ventilation types. (Exhaust) |
| Power Vents without a humidistatic control |
| Bathroom Vents exhausted into attic |
| Over insulation of the attic floor |
| Under insulation of the attic floor |
Intake Ventilation
Lack of adequate soffit (intake) ventilation is by far the most commonly made mistake in roofing ventilation. For roof (exhaust) vents to work efficiently there must be a source of replenishment air. If you have ever poured gasoline from a small can,you may have noticed how slow and inefficiently gas flows from the spout without the little vent opened on the other side. All roof exhaust ventilation products act in similar fashion. Without balanced intake versus exhaust, expect higher roof and attic temperatures in the summer, and elevated moisture or condensation in the winter. All roof systems must have intake ventilation!
Exhaust Ventilation
In most cases, exhaust ventilation products should never be mixed or used in conjunction on the same roof. If a ridge vent is used, power or static ventilation should not be used. If a power fan is specified due to lack of ridge line like on large hip style roof, there should be no other exhaust ventilation present. The idea that more is better seems logical when dealing with roof ventilation. But it is disastrously wrong!
When a power fan or even static ventilation is placed on the same roof as a ridge vent, the ridge vent becomes intake ventilation. Elementary physics gas laws tell us that when the power fan is powered on, it will draw air from the place of least resistance.
More simply, instead of the soffits acting as intake, the power vent draws the air from the ridge vent. This results in moisture retention and is definitely a major contributor to roof failure and attic mold growth.
Different ventilation types should never be used in conjunction with one another.
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