Cold Climates - Laying Out Over Existing Insulation is Best.
In cooler climates, laying foil insulation over the existing insulation is usually the best method because our main concern is to keep the heat IN during cold weather. Being a Texas guy, I honestly don't have a lot of first had experience with this install method. However, I'm always amazed at how many customers from the North order foil after seeing the results their friends or neighbors. I hear they are both saving money and even more often I hear how much installing radiant barrier foil increases the comfort level.
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| Lay the foil across the existing attic insulation. Use a pole, stick or a 1x2 board with a nail on the end to "push" the foil back into the hard to reach areas. Overlap the seams just about an inch. The seams DO NOT need to be taped. Use a piece of tape about 5" long and apply to seam about every 3-5 feet to secure the pieces together. Be SURE to read the warnings below about the dangers of air leakage and too much warm moist air coming in under the foil insulaiton. | Cut loosly around obstacles. You can then tack the foil back together with a small piece of foil tape. Do NOT use duct tape. Try NOT to compress the insulation and try to leave about a 1-2 inch gap between the foil and the top of the insulation. For larger areas, you can lay out the foil in sheets and tack them together to form a large piece of foil. Then roll or fold up the foil, take into the attic and lay it out. |
How it Helps in Cold Climates:
It's called the "R-Value Myth" - Look it up. Basically, it says that the R-Value of insulation is tested in a lab and air movement is zero. We know that air flows quite nicely through fiberglass. Ever looked at most AC filters? Fiberglass right? In walls, for fiberglass to be fully effective, it must be surrounded on all six sides to minimize air infiltration. Now, look in your attic. The top of the insulation is wide open and exposed to air currents. This is why jackets have an outer/inner shell that is "windproof". Take off the shell on a jacket and walk outside on a cold windy day. You will freeze your backside off.
Inside the attic, there can be a huge differential between the temperature inside the building and the attic. For example, if the attic is 20º and the living space is 70º you have a 50º difference. You get what is called "Convective Looping". This is when cold, dense and heavy air falls through the insulation and displaces the warm air against the living space.
Installing foil on top of the insulation acts like the windproof shell on a jacket. It helps minimize the convective looping within the insulaiton. Perforated Radiant Barrier Attic Foil is NOT a vapor barrier. So, it WILL allow moisture in it's vapor form to pass through.
The other reason radiant barrier foil helps in cold climates is the reduction of radiant heat loss from the living space. It's like when you wrap a potato with foil to keep it warm. The potato will not "emit" as much radiant heat. This is called "Emissivity" or the ability NOT to release heat. By laying the foil on top or your insulation, you help keep the heat "IN" by not releasing it in the form of radiant heat. Radiant Barrier Attic Foil will has an emissivity rating of .03 meaning it will ONLY release 3% of the heat by radiant energy. This is why so many customers report a noticeable difference in comfort and less problems with rooms being hot and cold.
In Cold Climates follow these WARNINGS!!
Check for air leaks in the ceiling. Although the radiant barrier foil is NOT a vapor barrier, there is a potential for moisture to condensate if too much warm moist air is leaking out through the ceiling. In areas of cold weather, THIS CAN NOT BE EMPHASIZED ENOUGH!! Can lights, fixtures and attic doors are the main culprits of air leakage. These leaks should be sealed up BEFORE installing foil. Also, if you have any duct leakage, the home can be put under positive pressure. Since positive pressure makes the air get PUSHED out of the homes, even a SMALL hole can allow a lot of warm-moist air to get pushed into the attic.
Too much moisture and the foil will NOT be able to keep up and allow the insulation to dry out. Foil does not CAUSE moisture. Moisture causes Moisture. The trick is to eliminate the SOURCE of the moisture. If you are installing over a standard sheetrock ceiling with no holes/penetrations then the foil will handle any moisture vapor passing through.
Do NOT compress insulation. This will reduce the drying potential for the insulation and reduce effectiveness.
Lay the Radiant Barrier Foil LOOSELY over the attic insulation. Do not press into insulation. Your insulation will have some peaks and valleys. This is OK. In fact, if you can get a 1-2 inch gap between the foil and the top of the insulation and only have about 10-20% surface contact with the foil is ideal.