For Tall Attics with a High Ridge
The Flat Top method answers the question, “How am I going to get foil way up to the top of my attic?” The good news is you don’t have to get the foil to the top of the attic for it to be effective; it doesn’t really matter if the foil is 6 inches or 10 feet away from the roof, the foil will reflect the heat. We developed the Flat Top method to make installations in tall attics easier, faster and safer.
This method is the ideal radiant barrier installation method for both high pitch, hard-to-reach attics and standard type attics. The basic system involves creating a false ceiling that will act as flat surface to hold radiant barrier foil across the top part of the attic. This makes access within easy reach for even the tallest attics.
You do not have to create any ventilation and can essentially create a room within the attic made of radiant barrier reflective foil. Combined with proper attic ventilation, radiant heat will be reflected back towards the roof. Ventilation from the soffits to the ridge (highest point in the attic) will allow the heat to escape out. Even on the hottest days, the space within the foil cavity should be just a few degrees above outside temperature.
Measuring, Cutting & Getting Started
Most of the install process is like the Open-Ridge radiant barrier method, with a few changes. For this method, it is best to start at the top and then work your way down toward the eaves (this is opposite of the Open-Ridge method).
The first step is to create some form of grid or false ceiling to support the foil in the flat area. Remember the foil is not that heavy, it is about 5 ounces per 100 square feet. This is about the weight of a heavyweight blue painters tarp. You can use just about anything to support the weight of the foil: wood, wire, warehouse strapping, duct strapping, bungee cords, etc. foil.
The photo on the right shows metal strapping being used to create the grid to support the foil.
The best height is usually about 7 feet off the attic floor. For most attics this will be above the duct work and allow you to reach the foil without using any ladders. Many customers who have very tall attics will use a step ladder and take it up to about 8-10 feet to provide extra storage space.
Make sure to measure the distance down the slope to the soffits. Depending on the steepness of the roof, 3 rows of foil might fit perfectly (12 ft). You can adjust the height of the Flat Top to meet the top of the foil on the slope. This can save materials and having to cut the foil.
Creating the Grid/False Ceiling
The easiest way to make the grid is to purchase some metal duct strapping (with or without holes – it doesn’t matter) from your home improvement store, or you can get it from and air conditioning supply company. It is thin metal, cuts easily and it can easily screw into the roof rafters.
Other grid materials can be: nylon duct strapping, wire, wood, or rope. Just about anything that can be pulled across the attic and fastened to the rafters will work. Many contractors have been using heavy-duty strapping material used to wrap boxes and crates. You can get it at www.uline.com, www.grainger.com, www.globalindustrial.com, or you can check local hardware stores.
How far apart should the straps be? That is completely up to you, it really does not matter. The closer they are to each other, the less drooping of the foil between them. Probably the ideal distance would be about 7-10 feet between straps.
If you have an odd shaped attic, don’t over think it. It does not have to be perfect or pretty. You can even crisscross straps if needed. You just want something to hold up the foil. The main thing is to just try to get all the strapping fairly level so your foil will end up level.
Attach one end of the strap to the rafter bottom and pull across the attic and attach to the other side, while you do this, try to keep it level. As we mentioned above, the metal straps work best, but other materials will do.
TIP: Use 1⁄4″ hex head screws about 1-1⁄2 inches long and a magnetic nut driver with a cordless screw gun. This way you can use one hand to hold the strap and one hand to hold the screw gun without the screw falling out.
Use one screw to hold the strap and a couple more to tighten it in. One metal strap can easily span up to 20-40 feet. Figure out a pattern to run the foil on top of the grid and start running pieces across the top of (above) the strapping.
Securing the Foil to the Straps
Use foil air conditioning tape (available at local hardware/home improvement stores) to secure the foil to the first strap. Run the foil all the way across the grid and let it hang loosely.
Then have your helper pull the far end of the foil tight. Go back to the second strap and tape the foil to that strap.
Keep tension on the foil so it is taut and continue to tape the foil to all the straps until you reach your helper at the other end of the space.
This method will keep the foil straight, tight and neat. Install other pieces on the flat top and overlap them a couple of inches until the flat part is done.
Ventilation in the flat top method is a good idea, especially if you have a whole house fan or an upper and lower attic with air flowing into the upper part.
You should cut a few holes (or slits) about 1 square foot each, to allow air to move properly and to promote good ventilation.
With this method a triangular pocket is formed above the Flat Top part. Heated air will from the roof line will pool and collect in this pocket and find it’s way out of your top exhaust vents.
If your bathrooms fans vent into the attic (which is a bad idea by the way), you should also cut some holes in the flat top to allow moisture to travel out of the attic. Even though the foil is perforated, it’s never too much to have air flowing, especially when moisture is a potential concern.
If you live in a cold climate, you should definitely cut several holes in the top and cut a slit in the foil around the lower part of the roof. In colder climates good attic ventilation is imperative to prevent moisture from the home from condensing when it meets the cold layer of foil. Of course the best way to do this is to seal up any and all leaky areas from your home into your attic.