The goal of adding a radiant barrier in your attic is to cover as much of the underside of the roof as possible. You want to add the foil on all surfaces that make up the roof, but you also need to keep vents open and clear of the foil.
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Step 1: Determine How Much You Need.
For stapling foil up, you need the flat square footage of the attic space (length x width) and then you will need to multiply that number by one of the following pitch factors:
LOW: Roofs under 8 ft tall from inside the attic = Sq Footage x 1.2
MEDIUM: Roofs between 8ft and 10 ft tall from inside the attic = Sq Footage x 1.3
HIGH: Roofs higher than 10ft tall from inside of the attic = Sq Footage x 1.4/1.5
For really high roofs, you should consider doing a Flat Top Installation for Radiant Barrier For Tall Attics.
Example calculation: Attic area of 55 x 35 = 1925 sq ft x 1.3 for a medium pitch roof (about 8-9ft high at peak) = 2,503 sq ft. So you would order 2,500 sq ft of AtticFoil to cover an area this size.
Step 2: Measure and Cut the Foil Before Going in the Attic.
This step makes the installation go easier because it minimizes cutting time and the foil is easier to maneuver in the attic when it is pre-cut.
Count the number of rafters in your space and measure the distance between a few random sets. Generally rafters are about 2ft (24" apart). Get the total number of rafters and multiply times 2 then add about a foot to the total length just so you don't run short.
Cut the foil - this can easily be done on a sidewalk or in the driveway. Cut several pieces at a time and then fold/roll the pieces up to take in to the attic.*
*Folding the foil or getting it wrinkled will NOT affect how well it works - smooth or wrinkled the foil still works the same!
Step 3: Start at the Bottom of the Attic & Work Toward the Peak.
Staple the foil at one end of the attic and then pull/stretch the piece across the whole space, adding about 3 or 4 staples to each rafter you cover. This will make the foil secure and minimize sagging or a loose install.
Remember to leave a gap along the bottom of the foil so the soffits can bring air into the attic, just like they normally do.
After your first run is complete, go back to the starting side and attach the second run, overlapping it an inch or two with the first one. *There is no need to tape the seams/overlap - just lay one piece over the other and staple it. Continue like this until you are about 3-6" from the peak of the roof then stop. You want to leave a small area at the peak uncovered for proper ventilation. This is true regardless of the type of venting you have! Read more about leaving gaps in your radiant barrier foil installation for proper attic ventilation.
Step 4: Cover Gable Walls
As your last step, go ahead and cover any gable walls in the attic. Gable walls that catch sunlight from outside will radiate heat into the attic space, so covering them will block the heat transfer in this portion of the attic.
Just like with your roofline installation, make sure you do not foil over any vents or fans. Cut the foil out around those exhausts and cover as much of the wall as you can get to in order to get the best results.
Step 5: Enjoy a More Comfortable Home!
You did it! That's it!
Now sit back and watch how INSTANTLY your home doesn't get hot as quickly in the day. Another side benefit to this is that many people use their A/C units less in the summer once they install AtticFoil Radiant Barrier.
If you have any photos to share of your own installation - please do!