Building Gable Vents

Written by john landers | 13/05/2017

Building gable vents is one of the simplest ways to vent a hot and steamy attic in the summer months. They are located in attic walls near the point where the sloping roof sections come together. Gable vents are also useful during the winter season for venting excessive water vapours that emanate from the living space. Improper attic ventilation can lead to the formation of mould and mildew, wet insulation and rotten framing.

Building Code

Local building codes specify the minimum ventilation requirements. For example, most codes mandate one square foot of ventilation for each 150 square feet of space. If there is a vapour barrier installed in the attic or there is an even distribution of intake and exhaust vents, the requirement is one square foot for every 300 square feet of space.

Types of Vents

There are multiple ways of building gable vents into a structure. Usually, a gable vent is installed at each end of the house. Decide whether you want to install static, solar or electric-powered gable vents. Static vents are also called wall louvres. They have limited effectiveness and often result in hot spots in the attic.

Solar power vents are energised by the sun and operate during the day. They are inexpensive and effective in removing warm air. Electric-powered gable vents function automatically and power on and off based on temperature and humidity readings in the attic.

Sizing

To get the proper air circulation, it is important to have a balance mix of intake and exhaust vents. Intake vents allow cool air into the attic and are installed in the lower section of the walls near the eaves, which are the edges of the roof. Exhaust vents, such as ridge and gable vents, remove warm air. Since warm air rises, exhaust vents should be installed near the near the peak of the roof.

Half of the required ventilated area should have intake vents. The other half should have exhaust vents. To properly size vents, look for the "net free area" of the products.

Installation

Build the vent frame out of 2 by 4 stock. Usually, a 1/8 clearance is required around the perimeter of the frame. Cut the opening with a reciprocating saw. Install building paper around the perimeter of the framing and staple it in place. Apply a bead of caulk on the underside of the paper, which serves as flashing to prevent water penetration. Lap the top strips of paper over the bottom paper strips. Install a metal drip cap under the building siding and under the flashing at the top of the frame.

Install a mounting board for powered gable vents. The mounting board creates a sealed box, which separates the fan component from the exterior louvre. Attach the vent to the mounting board. For solar-powered gable vents, mount the solar panel on the roof. Wire electric-powered vents according to the wiring diagrams. Mount the louvre to the exterior wall. Attach the louvre flange flush with the exterior wall. Repair the siding as necessary.

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