The History of ExcelVent
In the late '80s I had the opportunity to be Project Manager on a large condominium project in Killington, Vermont. These upscale condominiums had many cathedral ceilings. The architect went to great lengths to design a roof system that would have a 1.5 inch venting space just below the roof sheathing to protect the roofing and prevent ice dams. Despite our best efforts we still experienced ice dams. In an effort to solve the problem we did infrared photography of the condos and discovered that the sheathing was not being cooled as expected. Upon further inspection we discovered that despite our design, the insulation was hanging up on the roofing nails and thereby blocking the space we had designed for ventilation. This led us to the conclusion that in order to preserve this ventilation space we would need a physical barrier to keep the insulation away from the sheathing. Over the years there have been a number of products that created such a barrier but all were stapled to the roof sheathing to maintain a continuous channel under the sheathing but none created the full-bay venting that would best protect all of the roof sheathing.(See IRC 2000-806.3 above) ExcelVent was designed to overcome these problems. In addition, stapled products typically get their structure from the staples and without them would collapse. ExcelVent's patented, self-supporting characteristic has inherent structural integrity that needs no staples and is therefore perfect for retro-fitting improperly vented rafters and greatly reduces installation time. Finally, the integrated vent baffle protects the end of the insulation and prevents wind wash. Below is an explanation of the Dynamics of Residential Attic Ventilation that will help explain the historic need for venting.
The
Dynamics of Residential Attic Ventilation.
In winter, many normal household activities such as running daily loads of laundry and clothes driers, dishwashers, cooking and showers generate large amounts of water vapor, as many as 22 pints a day. When this warm moist air leaves the home and enters a cold, unventilated attic the water vapor condenses back to its liquid state. This condensed water will damage the attic insulation, roof rafters, wood decking, underlayment and shingles through the destructive effects of rotting, mold and mildew. In summer, an unventilated attic will build-up heat that will cause the premature aging and cracking of wood and roofing materials and increase air conditioning costs.
Architects commonly address these attic moisture problems by designing and incorporating a passive and balanced attic ventilation system into the home. When a typical attic ventilation system is properly balanced, wind blowing over the high roof ridge vents creates a negative pressure that draws the warm, moist air out of the enclosed attic space. Fresh ventilating air enters the attic space through the low, exterior under eave (soffit) vents, bathing the underside of the roof sheathing with fresh, cool air, and then exiting at the ridge vents. Even in the absence of wind, the natural convection action of rising warm air still maintains a continuous cool airflow along the underside of the roof sheathing along the path between the low intake vents and the high exhaust vents.
In addition, during the winter months, by continually bathing the undersides of the roof with cold fresh air, we can prevent melting snow from running down the warmer roof and forming ice dams over the cold eaves, causing water-related structural damage to the roof, walls, and gutters. It's a very simple ventilating system that, when properly installed, works year around without any moving parts, without any energy consumption, and consists of just two simple, critical components, the intake and exhaust vents.
During
the 1950’s builders, installing attic insulation by blowing loose insulation
between the attic floor joists, soon after received complaints of
moisture-related damage in these attics. The culprit? The loose insulating
material had overflowed the exterior wall plate and entered the exterior
soffit or eave cavity thus blocking off the free flow of incoming fresh
ventilating air from the under eave vents to the attic.
Even
with properly installed insulation, wind entering the soffit intake vents
would cause the displacement of insulation or wind driven rain could soak
insulation near the soffit causing significantly decreased insulation
efficiencies and, in the extreme, water leaks inside the structure. As a
result, during the 1950’s and 1960’s a number of inventions, known as
insulation dams or vent baffles, were patented in an attempt to address and
control these attic moisture problems.
Drawing
of an old style vent baffle stapled to the sheathing.
With the advent of fiberglass batt
insulation, a relatively stable product, R-19 (6 inches high) attic insulation
could easily be installed between the attic floor joists over the wall plate
without blocking the ventilating pathway area above the exterior top wall plate
since the 6-inch batt insulation’s height was lower than the typical attic
floor joist height. As a result, the attic vent baffles and insulation dams went
the way of the dinosaurs and only one product was found in a small regional
marketplace.
The creation of an International Code Council (ICC) in 2002, successor to BOCAI, ICBO, and SBCCI, and the concurrent adoption of a new universal body of Residential Building Codes, much higher energy saving, attic insulation levels are now required and with the continuing requirement to install the attic insulation over the wall plate, the return of these old attic ventilation moisture problems is a sure bet. The attic insulation will now, in almost all cases, be much higher than the ceiling joist framing heights, thus instantaneously blocking off access to the low exterior attic intake vents. The ASHRAE derived drawing below illustrates blocked eave vents.
Although the attic vent channels or chute ventilation products currently
available provide for at least the minimum amount of ventilation air required
between the eave vents and the attic interior, most still leave the
exterior ends of the attic insulation exposed to wind driven rain and
accumulating moisture that can, over time, migrate from the soffit area to the
attic causing moisture-related damage to the roof sheathing, the wall, the
insulation and potentially internal mold conditions. This effect is illustrated
below.
