It doesn’t seem fair to have an attic cause your air conditioning bills to soar. The sun provides warmth, makes plants grow, and at the same time turns your attic into an oven.
Here’s how to get the sun to do double-duty, by helping to cool the same attic it’s trying to fry.
Install a solar attic fan, and not only does the same sun cool the attic, it’s powering the fan. Your utility bill drops twice- by not needing as much air conditioning, and not having to power an attic fan from the grid. Nice.
You will need:
- Jig saw or reciprocating saw
- Roofing nails
- Hammer
- Chalk
- Solar fan
- Ladder
- Roofing cement
- Soffit vents
- Utility knife and new blade
- Pry bar
Step One:
Choose the fan size according to the square footage of your house. The manufacturer will help you choose the right size and number of fans for your attic. It is okay to have more than one.
Step Two:
Plan to install your fan on the south facing side of your roof. If your roof faces in another direction, ask the manufacturer for the best placement. Developers don’t always build houses with the sun’s orientation in mind.
Step Three:
It’s not always easy to work inside an attic. My attic was a “scissor attic,” meaning the ceiling in the living room was arched, and I had no crawl space in the attic. I had to work solely from the outside.
Before cutting through the top of your roof, take all safety precautions and use appropriate gear. On a hot day, when you cut through the roof, the heat is going to escape rapidly- if your face is in the way, you’ll be hit with a wall of heat. I know.
Step Four:
Measure 20 inches down from the ridge, and place marks to center the fan between two rafters. Never cut through a roofing rafter.
Working from the inside or outside, drive a nail through the spot.
Step Five:
If your roof is high pitched, and you’re not comfortable working at a steep angle, hire a roofer to do the job for you. Just make sure they understand what you want.
Check the manufacturer’s instructions. The flange (the flat part) of the vent is larger than the hole you’ll be cutting. This allows the fan to mount to the roof.
Using a piece of string and the chalk, draw a hole the size you need. Tie the string to the nail you drove to mark your mounting spot.
Step Six:
Using your utility knife, cut through the shingles on the circle mark. (Remember to change the blade after this project). Using the pry bar, remove the roofing nails from inside the circle and the cut shingles. Do not remove any shingles or nails from outside the circle. Remove the tar paper. You should be looking at bare decking.
Step Seven:
It’s important to stop for a second and look again at your measurements. If the manufacturer says to cut an 18″ hole, and your rafters are 14″ apart, you can’t cut through the rafters. You’ll have to cut a 14″ hole for the safety of your roof. The fan will still function properly.
If you have to, mark a new hole and cut out with the reciprocating saw. Don’t worry about the cutout falling in.
Step Eight:
Using the pry bar, carefully remove the top two layers of shingles from the circle and the two shingles on either side of the hole. Do not discard- you’ll reseat these.
Step Nine:
Place a bead of roofing cement around the circle on the decking, and set the fan (oriented correctly according to the manufacturer’s directions) on the circle. Drive roofing screws or roofing nails through the holes in the flange to secure to the roof.
Begin to replace the shingles. Lay the tabs of the top shingles under the preceding layer, and drive roofing nails through the tab an inch next to the old holes. Do not nail through both layers of shingles- this creates holes for water to get through. Place a dab of roofing cement on the preceding layer of shingles and press down on the layer you nailed- this roofing cements glues the layers together.
The top layer of shingles will sit over the top edge of the fan’s flange, allowing water to shed off. The bottom of the flange sits on top of the shingles.
Step Ten:
The attic fan will begin working. It works by pulling air out of the attic, so outside air has to be pulled in. Read the manufacturer’s recommendations for how much soffit ventilation is needed for your fan to work at its peak performance.
If you need to add soffits, it’s easy. Find existing soffit vents under the eaves of your house. Measure to find out how far they are from the house, and match those measurements. Mark and cut out the same way (you won’t need a nail or a circle) you cut the roof. If insulation has fallen into the soffit, it may come out. That’s okay. You’re creating ventilation for the roof. Caulk around the new soffit.
Your attic will be cooler, so your air conditioner won’t have to work as hard. That will pay for the fan in no time.
Source: Tom Silva, “How to Install a Solar Attic Fan,” This Old House website, no date given
