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Eave ventilation

A code requirement for all newly constructed buildings and a topic of ever-increased attention on internet homeowner forums, television shows, and a requisite to qualify for both a manufacturer’s and an installer’s warranty, is well placed and adequate ventilation.

Standard attics and roof decks over vaulted or cathedral ceilings should be vented at both the top and the bottom, or the ridge and the eave.  Creating openings at both of these areas allows air to flow from the cooler lower portion of the roof to the upper openings as hot air rises and the attic routinely becomes comes very warm.  This convection from bottom to top is encouraged to allow heat to exhaust and dissipate as necessary. 

Many existing buildings have some ventilation provided at the ridge (usually not enough), but have little or no provision for a draw of air from the outside to supply fresh dry cooler air to the attic.  The effect can be likened to a drinking straw submerged into a glass of liquid.  If one were to block off the top of the straw and lift if out of the glass, the liquid would remain in the straw as the straw cannot draw in any air to allow gravity to do its work.  Even though there is a perfectly good opening at the bottom, the liquid cannot exit. 

While in the attic we are not relying on gravity to move the air, the principle is similar.  Air will move in very small amounts into and out of these vents at the ridge, but most of the attic space will be left with stagnant, hot or moist air if there is no opening through which air can enter.  A buildup of this hot air will eventually cause warping, blistering, and degranulation of shingles during warm weather.  As well, during the cooler seasons when the outside air is cold and warmth and moisture emanate to the attic from within the house, the moisture will not leave the attic and can cause mould, rot, and can even condense enough to show up as what looks like a leak inside the house.

There are many options for creating ventilation at the eave or adding to the existing venting to create an adequate amount of ventilation in the correct proportions: round louvered vents can be added to a wooden soffit from beneath, spaced evenly for air flow and aesthetics, some stucco or plaster soffits can be cut and fit with larger louvered vents reminiscent of heat registers, but in many cases the least invasive and most efficient solution is to add eave ventilation through the roof deck.  New products are available today such as DCI’s SmartVent and AirVent’s The Edge vent (see links for diagrams).  These vent strips are installed beneath the first course of shakes or shingles and create a continuous intake without disturbing the soffits.  With these in place, the attic can breathe and have a continuous through-flow of new air.

Even if you have a new roof but are not sure if the ventilation is adequate or correct, please email or phone us to book an inspection.  We may be able to help reduce the heat inside your home during warm weather, reduce the risk of mould and rot, and make your roof last years longer.