Energy saving radient barriers for your home?

Generally, those products do not carry an "R" value because the listing would be embarrassing.  They claim that the traditional "R" measurement is not adequate to gauge the performance of their "reflective" product.

Studies have been done though I haven't looked for awhile.  Basically, the reflective products seem to do better reflecting heat during hot months and as a result, I think the product does better in hot climates.  Also, an air gap is required to help the insulation value.  This may not be possible depending on where and how you plan on installing the product.

Often times these reflective products are used as a vapor shield around relatively cold duct work to prevent condensation.

Larry

I have some experience with it being put directly under a roof, specifically a metal roof.  I used to install metal roofing years ago and I know one customer with a very small house said that after we installed a green metal roof(which gets quite hot) with low-e(I've also seen it go by the name double bubble) it lowered his cooling bill by around $500 that year.  I have also just finished putting it under my metal roof on a cabin I am building. The difference between the low-e and without is amazing.  The metal without will literally burn you in the summer if you left your hand against it, while the low-e temperature seemed to be the same as ambient air. As far as other roofs I don't know the effectiveness, but for metal I would highley recommend it.  

http://www.radiantbarrier.com/double-white-insulation.htm

This is the stuff that I put on my cabin.

Goes211,

When I built my home in '03, the idea of radiant barrier plywood roof sheathing kinda fell through the cracks and standard plywood was installed. I considered retrofitting,  but after much inquiry I achieved a better understanding of the heat issues involved and I concluded that it was more effective to provide adequate attic ventilation than to retrofit with a radiant barrier material. In new construction radiant barrier plywood is definitely a good idea, but retrofitting was far more labor intensive. The material cost was higher also because it is cheaper to buy radiant barrier backed plywood than to apply an aftermarket material after having already paid the cost of the (non-radiant barrier) plywood roof sheathing. However, I've learned through experience and inquiry that probably 95% of houses in Southern California have inadequate attic ventilation and I would presume that to be true for the rest of the country. The Uniform Building Code (UBC)  requirements reflect a very minimum of eave vents and gable vent size and specify no ridge vents. By providing copious attic ventilation, a 'chimney' effect is created, providing a much cooler attic space and less heat entering the living space. Once the sun sets, a 'whole house fan' for evening use will quickly cool the house down to outside temperatures. I found this to be a much more effective solution.

As a side benefit, the lifespan of your roof will be lengthened, as attic heat will dry out the oils in the asphalt felt underlayment of your shingles much quicker.

This might not be the kind of barrier you are thinking of but it's easy to paint on: Hytechsales.com for hy-tech ceramic paintg additive which I have used to paint the inside and outside of your remodel job. I like this because it creates a fire-retardent (not a complete stop but slows it down), sounds proof, creates a hard shell on wood siding and hides some wall faults. I've used 3 coats before the final color but 2 is recommended.

EGP

I have used it for my attic and made window coverings for windows that face the sun in summer.

We have a concrete roof and the difference is noticeable. I have two fans that are thermostatically controlled in the attic and they run less now during hot weather, than before I installed the reflective barrier.

The most noticeable difference is when it is used in the windows. This lowered the temerature in my daughters room, which faces southwest. We have custom wooden blinds and low E glass, but when I put this stuff over the window, the temperature dropped 20 degrees inside. Its not pretty, but it saves a bundle on the A/C in summer.

My 2 cents worth. Your mileage may vary.

What others have stated or implied about best impacts in warm/hot months is correct.  It's solar gain collected and conducted by the shingles or what have you, to the sheathing and rafters that you isolate from attic air (which would pick it up via convection) with a radiant barrier.  The book Residential Energy by John Krigger and Chris Dorsi says you can expect 2% to 10% savings, for cooling, depending on climate and insulation level.

If you're willing to change your roof color to (near) white, you can get similar results.  There are paints for the purpose.  Some utilities have had Cool Roofs programs, so you might want to inquire about that.

deggleton - agreed, that's pretty much my take on it.  As far as insulating against the cold, some companies will show an "R" value that includes an air gap that may or may not be applied.

If radon is a concern, the reflective products claim that they provide a vapor barrier if applied under the concrete slab and around the perimiter foundation.  It makes sense but I am not sure how well and how long it works.

Larry

I believe there is next-to-no insulating value when there is no air gap, but with an air gap of some inches and a very careful installation there is some.  When there is no air gap, there can still be a benefit because the energy that's radiated goes nowhere.

I don't see a good reason to use a reflective product where there is no light and almost no temperature variation.  Heavy poly, when the sheets are sealed where they overlap, can be a vapor and radon barrier, probably at lower cost.

deggleton wrote:

I believe there is next-to-no insulating value when there is no air gap, but with an air gap of some inches and a very careful installation there is some.

Yup, I think the thermal resistance is overstated (Under uniform conditions it is the ratio of the temperature difference across an insulator and the heat flux) by the fact that manufacturers refuse to publish "R" values of their stand-alone product.  Air is a decent insulator so to add that to your product's effectiveness can be misleading.  That said, there seems to be some value in reflecting radiant heat especially with high temperature surface installations like steel roofs.   

Another problem with reflective insulation is that the effectiveness values do not comply with ASHRAE Energy Standards which are adopted by most states and jurisdictions.  If it is not code compliant, the value to the property may not be effected. 

BTW, are you an HVAC mechanical engineer?

Larry

Nope, not that.  Just one who came of age when energy became everyone's concern (more or less) and is nearly a BPI certified Building Analyst (waiting for my field exam to be scheduled, having succeeded in the written portion).