# How to Install Radiant Barrier on Attic Rafters in 5 Steps

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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!

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## 13 Discussions

I foiled my attic a few years ago after finding additional insulation I added was not yielding such spectacular results. In my case, there was no attic floor so I bought 4x8 OSBs, foiled them and screwed them on top of the joists. I still had plenty of foil left so I did the rafters too. WOW! The difference was tremendous! My home is a small ranch with a full basement. The house doesn't get as hot in summer as it did before and my heating bills are significantly lower despite some outrageously cold winters. Its fast, cheap and easy. Why not do it? My only comment is to ALWAYS use the perforated version so you don't create moisture problems.

Todd, thanks for the comments. Yes, the foil works incredibly well when stapled to the bottom of the rafters. Here is a Department Of Energy study that shows all things being equal, a staple up radiant barrier will reduce the overall heat flow (in Btu's) by 50%, which is a huge number! Department of Energy Radiant Barrier Study Results

I have a question about doing this in homes that have moderate to cold winters like Virginia. Does this stop the house from getting warm in the winter?

Heat always moves from hot to cold. So in the winter, heat is leaving the home. Sun exposure will help some to reduce the heat loss. Here are a few things to consider. First, the days are short, so you don't get as much sun time. Second, the sun is low in the Southern sky so the actual amount of radiant heat gain is much less than in the Summer. Third, a ventilated roof is designed to move cold air below the roof deck to keep it cold to minimize ice damming. This cold air "sucks" the heat out and although the shingles may get pretty warm, not much heat actually transfers via radiation into the insulation in the winter. Installing a radiant barrier on top of your insulation will reduce heat loss in the Winter AND reduce what is called "convective looping" in the insulation. Or, air movement from cold, dense air falling through the insulation which reduces it's R-Value. From what we have seen the benefit from reducing heat loss is equal or greater than the heat gain from the sun in the winter. Here is recent video we did explaining the Winter benefit: How Radiant Barrier Helps In Cold Or Mixed Climates

Just curious what negative effects this has when a leak starts to develop. Will the water just run down the foil and leak near the walls?

Ideally, the roof would not leak. However, with the "normal" installation of stapling up the foil, you start at the bottom and work up running the foil left/right. By doing this, a leak would only run less than 4 ft. (the width of the foil) before it would fall to the attic floor. Ultimately, if the leak was bad enough you would see a stain on the ceiling. Then, you could pull the foil down (it won't rip) and SEE a "trail" caused by the water marking the foil and find the exact start of the leak. Fix the leak and staple the radiant barrier foil back up.

It was helpful info from a project perspective vs. a heavy marketing push. I was talking with a co-worker about this the other day, so it was interesting for me to see the effort involved.

You don't typically see can vents and a ridge vent on houses, so I assume the can vents implies this house doesn't have a ridge vent. Based on that assumption, one thing that doesn't add up is the covering up past the can vents in the pictures. This seems rather inefficient since the bulk of the hot air would still enter the attic as it waited to be pulled down the newly created rafter channels containing the cans. I assume this implementation would be best in homes with ridge vents and second best would be were the application stopped at the cans as to not restrict airflow where a ridge vent isn't present. Does that sound right?

2 replies

You are actually seeing two different attics. One has ridge vent and one has static (or can vents as you call them). You want air to flow freely through the attic - really as though the foil is not even there. You will leave gaps at the tops and bottoms of each rafter bay. AND, if there are any other vents: wind turbines, static vents, electric fans etc. you will cut a hole in the foil directly below the hole. Basically, if their is a hole in the roof, you want a corresponding hole in the foil. You want to leave the gap at the top even if you DON"T have ridge vents. Hot air will rise to the top of the attic and "pool". Like water heading towards a drain. The air will seek a way out even if it's a little below. Essentially, it will be skimmed off. Finally, one thing to remember is that once you install a radiant barrier, whatever ventilation you have is usually enough. Kinda like parking a car in the shade, it does not really help to crack the windows. Typically the AIR below the foil inside the attic will be less than 10 degrees hotter than the outside (ambient) temperature. Here is a picture how to vent the hips where the rafters terminate on the hip rafter. Just cut a small hole/slit t allow the air to continue to the top. You never want the air to hit a "dead-end".

It's more informative than spammy. If you exclude the watermarks, the links are all pretty tasteful. (The watermarks are pretty rough, though.)

@AtticFoil: you're just barely on the right side of spamminess.

It was our first Instructable so thanks for the gentle corrections @wilgubeast! We will definitely keep them in mind as we continue to offer more Instructables on using radiant barrier. Thanks again!