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As an alternative to use a timber trussed tiled roof vent that involves removing tiles, can I instead replace two or more bricks, some on each end of my house, with wall vents like this?

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Presumably this would allow good cross ventilation... but would there be any drawbacks?

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Gable end vents were a common approach to attic ventilation decades ago, but those aren't nearly large enough. Gable vents don't provide the airflow that a soffit-to-ridge system does (via convection and vacuum), so they need to be quite large. A vertical loop is much better than the strictly horizontal circuit gable vents provide.

A rule of thumb is 1 square foot of ventilation for each 300 square feet of attic area. This number is typically used for soffit/ridge ventilation, though. What you actually need depends partly on the layout of the building, and whether some areas of the attic are remote with respect to the closest vent.

Then there's the fact that the vent in question doesn't offer much weather protection. Most gable vents are louvered, so that rain drains off even when driven by wind. You don't want your attic wall and the ceiling below rotting out due to regular wetting.

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Yes, gable end vents are great for attic ventilation, but the Code says Attic Ventilation shall be “cross ventilation “ and shall be 1/150th the area that is to be vented. (See ICC R806 Vents.)

However, there is one exception: The attic ventilation can be reduced to 1/300th the area to be vented provided one of the following items are met:

1) a Class I or II vapor retarder is installed on the “warm-in-winter” side of the ceiling, or

2) not less than 40% and not more than 50% of the ventilation is located in the upper portion of the attic. The upper portion is defined as: “Upper ventilation shall not be lower than 3’ below the ridge or highest point of the roof. “ (See ICC R806.1.2.)

So, you can see there is clearly a benefit to having ridge vents, gable vents, etc. , but in a proportion that allows COMPLETE CROSS-VENTILATION in the attic.

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