The subject of attic ventilation comes up frequently, both in summer and winter months; for those of us in the roofing industry.
During the summer; questions from consumers arise because many experience circumstances where they have difficulty cooling portions of their home, particularly on upper floors.
In the winter; people experiencing issues with ice dams or condensation, inquire whether they require some form of additional venting to resolve their issues.
The fact is, attic ventilation is necessary for a variety of reasons but is sometimes only part of the equation for resolving specific comfort problems.
In very general terms; proper attic ventilation is required to exhaust hot, moist air from the attic of a home or building. The key to properly venting an attic involves intake venting achieved through the soffits of the home, and exhaust venting, which is typically located near the top of a roof.
The ideal situation involves a balanced ventilation system where there is fifty percent intake, and fifty percent exhaust. In some home configurations, this can be difficult to achieve due to the construction /design of the roof.
Examples of attics that are hard to ventilate properly include homes that have gambrel (barn) style roofs, homes that have mansard walls, very low pitched roofs and vaulted ceilings. Other common examples include mixed types of attics such as conventional open attics which intersect roof areas that are vaulted.
Another example is older homes where roof rafters are pocketed into brick walls, so there is effectively no external soffit, or which results in an open under-hang configuration. Another common example is interrupted attics, usually characterized as having some form of living space beneath the roofline. Such attics typically have lower knee wall cavities near the floor and a small triangular attic space above the ceiling. Such spaces can also be identified as having sloping walls that mimic the roofline above.
Homes having flat roofs can sometimes require specific attention to how the assembly will be ventilated.
As a result; unusual configurations sometimes require non-conventional solutions. In most instances a qualified architect, or a competent roofing or building contractor, can prescribe a solution. In some circumstances, an engineer having a specialty in the roofing/building envelope field, should be called upon to investigate and supply specifications to handle a tricky situation. That approach further supplies the home or building owner with a measure of responsibility pertaining to the resolution of the issue.
Also to consider the subject of proper attic ventilation; are what are the other inter-related building components that need to be considered in the design of the system. Such examples can include attic insulation levels, air sealing requirements, access, extreme weather conditions, and roofing materials being used ( metal roofing is a good example).
It is important to note that the National Building Code, and all roofing manufacturers, require a balanced ventilation system. Where roofing product manufacturers are concerned; their product warranties may be voided if the proper attic ventilation is not provided.
There are different types of vents that are used to achieve proper attic ventilation.
In conventional “open” attic designs; it is most typical to use individual static roof vents in combination with continuously vented soffits, or soffits that have a determined number of individual grill type vents.
Vaulted /cathedral types of ceilings require continuous ridge venting, in combination with continuous soffit ventilation. This is because the cavity created between each roof rafter space is like an attic unto itself. Air must pass from the soffit upward through the rafter cavity, to be pushed out through the ridge vent.
As a side note; when thinking about attic ventilation; it is important to remember that heat rises. The function of the soffit (under-hang) vent is to introduce cooler exterior air into the attic which effectively serves to push the hot, moist attic air through the exhaust vents located near the top of the roof.
Other forms of attic ventilation include damper vents which are designed to exhaust bathroom moisture out through the roof as opposed to depositing it into the attic space.
There are purpose type vents such as those used to exhaust kitchen stoves or indoor pool areas. These are typically power-driven units.
Turbine vents are suggested to be used in circumstances where there may be a limited opportunity for intake ventilation. They are not recommended to be used in combination with static type roof vents, as they can act to draw air from the upper roof vents through the turbine vent. Because such vents are driven by the power of the wind; a spinning turbine literally sucks air through the mated vents.
Power-operated roof vents are another option for circumstances where excessive heat build-up in an attic, in combination with limited intake ability, can be employed. Such vents typically are rated for a prescribed number of cubic feet per minute (CFM rating). In other words; the type of power vent used needs to be calculated. Such vents are hard-wired and are thermostatically controlled. An electrician is also required to complete the hookups legally.
A variation of a power vent uses solar power to drive the electric motor, and are often less expensive to operate. They are reliant on a fairly consistent light source, and so may not be an optimal choice for cold climate regions.
Related Content: Attic Ventilation and Its Importance
Large capacity static vents, such as those manufactured by MAXI- Vent™, can be substituted on conventional attic installations in lieu of a number of individual static vents. Such vents are designed to work well in areas where high snow volumes, can be troublesome. Their design including internal baffles, and high profile design, help avoid ingress from extreme snow volume or driven snow; which can be problematic for certain other types of roof vents.
Slot vents are a type of intake vent that can be installed lower down on the roof surface, where soffit venting may not be an option as a result of roof design. In principle, they are similar to a ridge vent but designed to integrate into the courses of roof shingles, toward the bottom of the roof. They may not be the best option for areas that receive sustained or high volumes of snow.
Gable end vents are a type of vent which is located on opposing end walls below a gable style roof. The design is centuries old, but can be effective under the right circumstances. Such vents typically have a grille type of design with slats designed to shed water. Behind the grille, should be filter screens that prevent bugs and dirt from entering the smaller attic configuration.
As with any attic related ventilation system; a proper calculation needs to be made to achieve the right mix and number of exhaust and intake vents. Most ventilation manufacturers provide charts and specifications designed to aid the designer, builder or roofer to calculate the correct venting configuration.
As with all roofing related products; some are better than others. As an example, metal static roof vents are considered better than plastic-type vents, because they are more durable.
Homes of today are being constructed with a view toward greater energy efficiency. Such homes are being built with higher levels of internal wall and attic insulation, higher efficiency furnaces, airtight windows and doors, etc.
While this good, it then requires that the home’s ability to “breathe” must increase. This is necessary to avoid premature rot of wooden building materials, combat humidity, and condensation build-up in winter months, and to maintain a healthy living environment for the building’s occupants.
With that principle in mind; older homes that have been renovated or upgraded to incorporate modern building standards should be ventilated correctly.
The opportunity to improve a home’s ventilation presents itself when the roof is due to be replaced when insulation levels are being increased, and or air sealing methods have been employed to mitigate heat loss from the building space and or attic, (the greatest factor contributing to ice damming); and when undergoing remodelling or renovations.
The National Building Code, and the CMHC, as well as ventilation product manufacturers, have a wealth of information available online to assist consumers with educating themselves on the subject and requirements of proper attic ventilation. You are also invited to learn more by visiting or contacting AVENUE ROAD ROOFING® www.avenueroadroofing.com