First, let me say:  Radiant Barrier is NOT a substitute for “Regular” types of insulation – either fiberglass insulation or cellulose insulation.  Radiant Barrier and regular attic insulation work TOGETHER to make your home more comfortable and energy efficient.

People always ask. “Should I Add More Attic Insulation or Install A Radiant Barrier”?  I hear this often and the answer is usually BOTH.

Regular attic insulation slows conductive heat.  Radiant barrier reflects radiant heat.  Your home gets a lot of both. Think of your home as a big refrigerator.  How much heat that flows in or out of this big box is determined by basically three things:  1) Inside surface temperature, 2) outside surface temperature and 3) R-Value and thickness of what is between the inner and outer surface.

The walls and top of the refrigerator (or your home) are typically insulated with “regular” insulation. Regular fiberglass or cellulose insulation slows conductive heat. Radiant Barrier acts like shade to reflect radiant heat and make the regular insulation more effective.  A perfect home would be built like a well-insulated refrigerator and be wrapped with radiant barrier foil insulation.  Common sense says that a refrigerator in the shade will use less energy than one in the direct sun.  This is because exterior surface temperatures can easily exceed 150º in direct sun.

If you decrease the outside surface temperature and reduce the difference between the inside/outside temperature, this has a similar effect on reducing heat flow as adding MORE “regular” attic insulation.

Too much of a good thing.

Getting attic insulation up to the recommend level for your area is always a good idea.  However, at some point you reach the law of diminishing returns.  Why?  Regular insulation slows heat, but it also HOLDS heat.  At the end of a hot-sunny day, the insulation in your attic can become a big, thick 130º blanket over the top of your home.  When the sun goes down, this “hot blanket” effect continues to hold and drive heat into the home. Once the roof cools down, the insulation can easily be the hottest part of your whole house. This can make your air conditioner run later into the night.  If you have marginal attic insulation, installing a radiant barrier will make what insulation you already have even more effective.

By combining good attic insulation and radiant barrier, you will get the best of both properties.  Reduction of conductive heat flow AND reduction of radiant heat flow by decreasing surface temperatures of the attic insulation.  Lower surface temperature is like putting the house in the shade.

So, for most homes I recommend doing both.  For maximum benefit, top off your existing insulation AND add a radiant barrier.  They will work together for maximum comfort and energy savings.

 

I've written several other posts on this that you might be interested in. Check these posts below:

  • The #1 Attic Ventilation Problem
  • Combining Radiant Barrier with Spray Foam Insulation
  • Four Silver Bullets For Saving Energy In Hot Climates
  • Attic Insulation & Radiant Barrier Work Together In Warm Climates
  • Attic Ventilation – Don’t Mess It Up
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    15 Comments to “Attic Insulation & Radiant Barrier Work Together In Warm Climates”

    1. Eben Stiefel says:

      In Hawaii, we normally insulate the attic ceiling…not the attic floor. We have good ventilation (tradewinds) and not usually moisture problems. We don’t have to worry about keeping warm air in the house because it doesn’t get cold outside. So it is usually EITHER a radiant barrier OR fiberglass. In my case I only have 2 x 4 truss top chords so can only do R13 bats and can not decide which would be a better product if I have to choose only one. Of course I could insulate the attic floor with bats AND the ceiling with foil..but not in the budget and I think overkill in our relatively temperate ‘paradise’. Uninsulated the attic easily gets over 120, even 130. but I have put R19 in 2 x 6 roof joists and that kept the attic to 90 or 95..very comfy.
      Basically because I only have 2 x 4 I was wondering if foil might be better?

      • Ed Fritz says:

        Eban,

        You basically need an umbrella for you home. I’d use radiant barrier on the roof and then (if needed) add insulation to the attic floor later. Insulation on the roof helps, but it’s really the wrong placement of R-Value. Example: I can hold a jacket over my head and it ACTS like an umbrella – right? Why not just use an umbrella?

        If you have good attic ventilation as you stated, then a radiant barrier should drop attic air temperature. However, AtticFoil® Radiant Barrier will REALLY drop the surface temperature of your ceiling. This is the heat you FEEL coming into the home. Try it, you will be very pleased.

        Please send some pictures of your installation in warm Hawaii – It’s been COLD lately here in Texas.

    2. Mark barrow says:

      I live in warm middle Georgia. what do you think of radiant barrier versus foam insulation for mostly warm climates? Also, what do you think would work best for cooling off a bonus room over a garage which is hotter than other upstairs rooms?

      • Ed says:

        Mark,
        Radiant barrier should never be a substitute for regular insulation. Refer to the Department of Energy for the recommended insulation levels and follow that guide – then add a radiant barrier to the attic for optimal results. Being in a mostly warm climate, you’re greatest benefit will be the heat reduction in the summer months. As far as how to approach a bonus room over the garage: if the garage door/walls catch direct sunlight, then add the radiant barrier on the garage ceiling, to make a big impact on the temperature in the room above the garage. However, if the roof area above the garage catches sunlight as well, then you should also add radiant barrier above the room, since it is probably absorbing the majority of the heat from the roof catching direct sunlight. Think of it as looking for shade from the HEAT; the foil is your shade so to speak. For more info on hot rooms, read the article I wrote: Hot rooms in my house – how to make them more comfortable.

    3. Chris B says:

      Hi. I live in Columbus, OH. I have been recommended to your site. I have been doing lots of research on whether to install insulation on the attic floor or the roof joists. I have also seen on a .gov site that it is only recommended for warm climates, not cool and that you shouldn’t install on the attic floor which is contrary to your recommendations for certain situations. I have two questions: 1. Is Columbus, OH too far north for the radiant barrier to be effective? 2. Is installing the barrier on the floor, even perforated, a likely cause for warm air to condensate under the barrier on my fiberglass insulation in the winter time?

      Thanks for the information. I look forward to your response.

      Chris

      • Ed says:

        Chris,

        No, Ohio is not too far north to have an effective radiant barrier; we have customers in Northern Canada! What makes a radiant barrier effective is one thing: a source of radiant heat. This source can either come from direct sunlight or from inside your home (heating unit).

        About the condensation issue – it’s important that it’s clear that foil does NOT cause moisture. The meeting of two drastically different temperatures causes moisture (think of someone’s HOT breath on a COLD window – that condenses and causes moisture). Now if your ceiling (aka attic floor) is not air tight, then it is possible that warm air escaping through the ceiling into the cold attic in the wintertime can present an opportunity for moisture to occur. To combat this you need to make your ceiling airtight. The foil is perforated, which does allow small amounts of moisture to pass through it and evaporate. However, large amounts of moisture could get trapped behind the small perforations, so air sealing is a priority. For more information on sealing common culprits of air leakage, check out this page on the AtticFoil.com website: How To Install Radiant Barrier Over Can Lights

    4. Paul says:

      I am getting ice lams after having a new roof installed along with venting the peak , I am in the process of installing
      soffit venting along the whole soffit area, I have a 1400 sq
      foot home and am putting in a 5.5 continuous screen along
      soffit. Am I over doing it?

      • Ed Fritz says:

        Overdoing it? It really depends. It sounds like you will have plenty of air coming in the bottom. Do you have enough open area at the top for the air to get out? I like wind turbines in cold climates since the you don’t get much stack effect, but the wind WILL draw air out of the top of the attic. Finally, have you thought about installing a Radiant Barrier To Prevent Ice Dams?. We have had many customers see a significant reduction in ice dam issues after installing AtticFoil Radiant barrier either by stapling to the bottom of the rafters or laying out over the attic insulation.

    5. john says:

      ed thanks for all the good information. my situation is a little different and i hope you can help. my customer (in the desert area of southern California) has a roof sheated with plywood with tecshield attached.The roof rafters are deep enough to accomodate an R-38 batt and leave approxamate 1′ dead air space between the top of the insulation and the radiant barrier.Does the 1′ dead air space have to be vented? what if the insulation touched the radiant barrier and the roof sheating?would there be issues with condensation? thanks john

      • Ed says:

        1. The airspace can be vented OR dead. Ideally, you’d like it vented because it keeps the roof deck cooler, but either one works.
        2. If the foil touches the insulation, then it’s no longer acting as a radiant barrier, but rather a conductor. Condensation could be an issue, not because of the foil, but because you’ve eliminated ventilation which is your primary weapon against condensation.

    6. Ellie Davis says:

      Thank you for pointing out that getting a radiant barrier can help balance with your insulation. My husband and I are needing to get new insulation for our attic and need to find the best company to help us do it. I’ll have to do some research and find the best company in our area.

    7. Rob says:

      I recently bought a home and in my situation my attic is half finished as a living space and their is another half that is enclosed directly next to it and is unfinished exposing the attic ceiling and so I installed baffles and batt insulation to try to reduce the heat radiant and it seem not to do much , the finish room was getting very hot compared to the downstairs, example 70 downstairs and the attic would be about 20 degrees hotter when sun is out. I just learn about the radiant barrier here and I wanted to ask if I can install it directly over the batts insulation on attics ceiling without any issues and help reduce heat ?
      Thanks

      • Ed says:

        The majority of the heat these 2nd story rooms feel comes from above, so if you can get foil up above the room, that’s going to be first priority! Then, yes – add *perforated* foil over the insulation on the walls of that room (kneewalls). You can staple the foil directly to the studs that frame the room, against the insulation – this will make a huge difference in the comfort of that room. More info here: Knee Wall Applications

    8. Chris says:

      I am in sunny florida and have fiberglass insulation stapled up against the rafters (r13 or 19 not sure)
      Now my blown in insulation is old and flat, I am considering cleaning that up, moving the insulation off the rafters to the attic floor, then stapling radiant barrier to the rafters.
      Is this a good plan? Thanks Chris

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