Which Install Method is Best?
We get this question daily. The problem is that it is hard to say since there are several factors to consider when determining the best installation method for a home. Every home is different, so while there are general recommendations for certain climates, sometimes one method is best for a particular home.
For the majority of installations, there are basically two different methods used to install radiant barrier foil in an attic. The first is stapling foil to the bottom of the roof rafters, the second is laying it out over the existing attic ceiling insulation. Methods like the Flat Top and the Hybrid are just modifications of the standard Staple Up method.
The main factor to determine the best method is to decide what your primary goal is and what is inside your attic. As a general rule, many people who are trying to reduce summer cooling expenses choose to staple the foil to the bottom of the roof rafters, while people looking for a winter heat retention benefit opt for laying the foil insulation over the existing insulation. Generally speaking, people who are in mixed climates or those who are looking for year-round benefits, typically opt for either a hybrid method or laying it over the insulation. Again, these are general rules.
The other main criteria is what you use your attic for and/or what is inside of it. When you staple radiant barrier foil insulation to the bottom of the rafters, you combine the benefit of having a cooler attic by putting your duct work in a less hostile environment with the reduction in radiant heat flow through the insulation. This method creates a greater total reduction in heat flow in warm climates versus laying the product out over the insulation. Period. Furthermore, it’s very nice to go into your attic on a hot summer day and actually be able to tolerate it. Invite your friends over, they will be amazed.
I want to keep heat out in the summer and keep heat in during winter. Which method does that?
Getting year-round benefit from radiant barrier is possible and in some cases only one layer/method needs to be done. In other instances, a combination of the two (hybrid method) will yield the best results.
If your attic is empty (no duct work, no HVAC units, no storage, etc.), then installing it over the insulation on the attic floor is always the way to go. This method blocks heat on the top surface of the foil during the hot months, keeping the insulation below the foil cooler. In cold months, when heat normally escapes off the top surface of the insulation, the foil layer will help keep the heat inside the insulation and that will help keep the house warmer.
However, many attics have items like storage or duct work inside them, which means they wouldn’t get the full benefit in the summer if they just had foil on the floor over the insulation. For example, if you live in a cold climate but you have an HVAC unit in your attic, a hybrid method of laying the foil down and stapling it up is probably your best method. Another example would be someone who is in the Midwest and they are planning to lay the foil over their attic floor, but they use their attic for storage. In this case they might opt to staple the foil up, or consider a hybrid method as well.
The benefit to the hybrid method is that if your attic contains items that need to be cooler for any reason, or if your attic floor is used for storage, then you can still achieve great year round results with the hybrid method. Even if you have flooring in your attic, you can still staple the foil on top of the wood flooring, as long as the foil remains uncovered (ie. you can’t store boxes on top of it).
More often than not, customers choose one method or the other, but the hybrid (doing both methods) is becoming more and more popular as weather is shifting and patterns are no longer predictable for certain geographic areas.
Bottom line: if your attic is empty other than insulation, lay the foil over the insulation. If you have items in your attic that are heat-sensitive, staple the foil up first, then add a second layer over the insulation to get year-round results.
I was told I needed to use an over insulation method – is that right for my house?
You will see other websites and many professional installers declare that laying the foil out over the existing insulation is best. There have even been some studies that show that putting the foil insulation over the existing insulation does yield better reduction in heat flow. I’m not arguing with this study and in fact it is probably accurate if you were only measuring heat flow through the ceiling.
The problem is the location of the duct work and/or the HVAC unit. In the South, we do something really stupid: we put the duct work up in the attic! Who decided it was a good idea to run 50ºF air through a poorly insulated (R-4 / R-8 insulation) pipe (that also probably leaks) and then surround it with air that is over 130ºF. This is like deciding to make ice cream in your oven…what are they thinking?!
Is laying the foil out over the existing insulation easier to install?
Yes, no doubt it is easier to install the foil this way, and I’m not opposed to this method even in predominately hot climates. It may not be the absolute best method to add radiant barrier to a home, but considering how much easier it is to install in general, it is often the best way to go. Additionally, this method uses less material than the other methods. If your attic is empty (no duct work, no HVAC units, no storage, etc.), then installing it over the insulation on the attic floor is always the way to go. However, there are many homes that have an attic space that is tight or crowded, that it’s almost physically impossible to get good access to staple to the bottom of the rafters. If you want to lay the foil out over the insulation in hot climates, you need to do the following to ensure maximum benefit:
- Determine if you have enough attic insulation. Radiant barrier foil is not a substitute for regular insulation. Foil is great, but it works in combination with regular insulation to make the regular insulation more effective. Check with the DOE (Department of Energy) for the recommended level in your geographical area.
- Check for air leaks in the ceiling. Although perforated (tiny pinholes that allow moisture to pass through while maintaining the full effectiveness)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. Can lights, fixtures and attic doors are the main culprits of air leakage. These leaks should be sealed up before installing radiant barrier attic foil directly over attic insulation.
- Check your attic ventilation. By increasing the ventilation you can reduce the air temperature of the area. This puts the duct work in a less hostile environment and will reduce heat flow in to the ducts as described earlier. Heat is flowing into the ducts by conduction, not radiation. So, no, you cannot just lay foil over the duct work and get the same effect. Good ventilation will put the ducts in a cooler environment.
- Attic ventilation is real simple: holes in the top of the roof (exhaust vents), and holes in the bottom (soffits or eves). The more holes you have, the closer to ambient temperature your attic will be. From being in thousands of homes, we can tell you, most homes do not have enough holes in the bottom of the attic to allow air into the attic. Even with bad/poor attic ventilation, radiant barrier will reduce heat flow into the home, but for maximum benefit be sure you have some decent attic ventilation.
It can be a tough choice to choose one method.
To be honest, it can be a tough call on which method to choose.
Stapling the foil up will afford you easier access to the attic, provide a cooler attic for your ducts to work more efficiently, keep any stuff stored in the attic cooler, and allow you to add more insulation later, if needed. Laying radiant barrier out over insulation is usually faster and easier, and it requires less material and more wintertime benefits. Either way you decide to go, adding a radiant barrier will have significant benefits to your home’s comfort level and energy consumption. Now, choose an install method, and get it done!
Bottom line: if you want to maximize the reduction in summer cooling costs, staple the radiant barrier to the bottom of the rafters. If you are looking for more year-round savings and an easier install method, then lay the foil out over the insulation. If you want both, consider what’s in the attic and then determine if one layer on the insulation will work or if you need to do both methods because of items in the attic space.
Also, don’t forget about the attic stairs! It’s a good idea to both seal and insulate your attic entry stairs, too! Doing this significantly reduces air loss, which can drastically lower your energy bill. It’s worth the time and effort for sure!