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MLMIB 06-27-2011 08:46 PM

radiant insulation
I'm trying to learn more about it. My dad saw some gimmicky presentation on it and to be honest there does seem to be some truth beyond it but I seem to find stories of either "it's the greatest thing" or "it's a scam and you don't need it". has anyone tried it? any experience?

if it helps I live in Maryland.


autx790 06-28-2011 05:41 AM

I recently put a radiant barrier in my attic. I looked at all of them and came to believe there is a lot of marketing gimmicks to the different products. Seems like they all try to make their product a little different and then say it's the best. If you've ever put tin foil in your window, you'll know the idea works. I ended up just getting the reflectix at lowes.
I put it up and then have also read reviews that you want to install a gable fan in your attic as well to get the heat out. I put the gable fan in and set the thermostat to 105 as recommended by the manual, but it wont come on unless i set it down into the 90s. It's been getting to about 100 degrees outside here and I still dont hear my fan coming on.

When you install it, they say to leave a few inches at the top open and a few inches at the bottom (by the soffit). I pointed an IR thermometer on the bottom side of the foil and measured about 90 degrees. I put it on the bottom side of the exposed roof and measured 120 degrees. I was about 3ft away doing this test.

I called reflectix and they said I needed the product which had the bubble rap between two layers of foil, but that was more expensive and I couldn't figure why that was needed. So called again and asked why I couldn't use the regular (cheaper) foil material, and they said I could and it would be the same in that application.

So I would say i'm pleased with the way it seems to work in my attic, but I'm not too sure you really need to install it somewhere that doesn't have the sun shining directly on it. I really only installed it on half my roof which gets pretty much all of the sun exposure. I'm not too sure how it would be effective in winter months in keeping heat in which i guess would be more of your need.

trebor1 07-04-2011 09:56 PM

i think radiant barrier does a great job of keeping your attic cool. I would only use it under the rafters not on top of insulation on the floor, I is not nearly as good for the winter though there would be some small benefit.

Gary in WA 07-05-2011 11:27 PM

In a cold climate it can negate the value. Bring your attic up to code (minimum), air-seal, and minimum ventilation. You want the solar gain in the winter...... Power fans have there own dangers.


HomeSealed 07-06-2011 06:56 AM

GBR is right on... From what I've seen, a lot of "sales" driven companies are pushing it to try and give the impression of being "green" and energy-efficiency experts. The reality is that most just don't want to do the dirty work up air-sealing, etc which is the REAL deal no matter where you are located.... RB can and does offer benefit in hot & sunny climates, but imo it is a waste if you live anywhere else.

operagost 07-07-2011 02:02 PM

My personal experience with my radiant barrier ( is no noticeable difference in winter heating, although that is difficult to determine because it would require a lot of precision on my part in recording the temperature and oil consumption. However, in the last month (the first with significant A/C usage here in SE PA), with an average temperature identical to last year I used 3.6 fewer KWh per day. Unfortunately, there are other changes to account for, such as replacing one 9.8 EER 10K window A/C with a 10.8 EER 12K unit. I'd say it's not all due to the AC, though, because frankly I hardly ever needed to turn it on. If you live in a mixed or hot climate and you are at R30 or less but unable to add more insulation, I would recommend it. Of course, you should always take care of the annoying but cheap fixes like sealing air leaks first. The "nice" thing about batts or blown-in insulation is that the dirt streaks tell you where the leaks are. :laughing:

trebor1 07-25-2011 05:50 PM

radiant insulation for cooling
[quote=GBR in WA;680566]In a cold climate it ( reflective insulation - my insert) can negate the value. Bring your attic up to code (minimum), air-seal, and minimum ventilation. You want the solar gain in the winter...... Power fans have there own dangers.

Thank you for all the links Gary. I was only talking about radiant for hot climates and assuming the home was already built and had insulation under the attic. I was also assuming the attic was unconditioned.

For a new home which I want for myself I would have a conditioned attic. I would put 4-6 inches of polyso on the roof decking to prevent condensation over the poly I would put a reflective sheet and then lay 2 by 4 on their side to create an airspace. I would then put another decking on the 2x4s which I would cover with light colored shingles. This would kind of be like a sip roof with an airspace. I would then space dense cellulose between the rafters to exceed the code and bring the insulation value up to r 60 which I think Martin suggested in one of his blogs. I am trying to follow the guidlines of r 10 under the slab r 20 for the basement walls, r 40 for the walls above the basement, and finally r 60 for the roof with a conditioned attic. This was in his blog on too much foam and the passivhous standard which he found to be to arbitary. This is, I hope, a more reasonable standard for super insulated homes. Does this make my short post clearer? Thanks again for your very good response and the links. I realize I have a lot to learn so if I am off base please let me know. Robert Nemoyer 717-766-5799 or

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