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How To Install Gable Vents




Randy I. from Mesa, AZ wrote:


I recently bought a older house and discovered it doesn't have any upper ventilation in the attic. I want to install gable vents. How do I go about this?

Gable vents are a good choice if you have a roof where it is difficult to install roof vents. Examples would be a tiled or metal roof where installation would be difficult. Ventilating the attic is very important. You need to get that heat out of there. It also helps control moisture that can cause dry rot of the structural members.

Gable vents are sold in units of "net free area". That is the specific amount of ventilation the gable vent will provide. 


For older homes without an attic vapor barrier a general rule of thumb is 1 square foot of "net free" ventilation is required for every 150 square feet of the attic. So, the first thing you'll need to do is measure the square footage of the attic. Once done divide the figure by 150 to determine how much ventilation is required. If your attic floor has a vapor barrier divide by 300.  Note: These are general calculations - I would strongly recommend checking with your local building code department before you get started. 

Next, you need to decide on which type of gable vent you want to install. You need to purchase two of them for each end of the attic to provide cross-ventilation. They are made of different materials, sizes and shapes. 

These are general guidelines for installing a gable vent:

1. First you'll need to build a frame to mount the gable vent to. Using 2X4's construct a frame between the gable studs. This is where the vent will be installed. Make sure it's perfectly square and allow about 1/8" free space on all sides. Once attached, either drive a nail at each corner of the frame through the siding or drill a hole in each corner. This is to enable you to locate the vented area from outside.

2. From the outside of the house, carefully climb a ladder to the area to be vented. Locate the drilled holes or nails you've driven through. Mark the area to be cut. If you used nails, remove them before making your cuts. Using a reciprocating saw cut out the opening. 

3. Flashing needs to be installed around the perimeter of the gable vent. You could use building paper, overlapping the bottom pieces with the upper for proper drainage. This can be attached using a staple gun with a good bead of caulk underneath each piece. Next, a metal flashing needs to be installed under the siding. Once done caulk under the gable vent mounting flange and mount the vent. Using nails or screws, secure the vent into place. Make sure it is plumb.

Finally, attach trim if necessary. Gable vents differ from manufacturer and style. If you had loose fill insulation in the attic and had to walk on it to get to the gable ends use a rake to fluff it back up to it's original condition. Compressed insulation will loose it's r-value. 

These are general guidelines. Make sure you look at the manufacturers instructions for complete details. 

Related Tips and Advice:

How To Install Roof Vents

How To Install Soffit Vents

How To Install Insulation Baffles


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