Radiant barriers - Bunk or real?

[turbo6bar]

Little brother and I are set to close on a new project foreclosure next week, which means I need to start laying out plans.

The house caught fire in 2005 and was partially rebuilt. The entire upper floor was rebuilt with new materials. New roof is on. Plumbing and electrical have been run and need to be taken to final. Basically, the house is a shell that needs insulation, drywall, and interior finishing.

That leads me to radiant barriers. Regular fiberglass insulation for exterior walls is around 40 cents per square foot. R-13 rating. A guy on eBay is selling radiant barrier for around 15 cents per square foot, and the barrier appears to have an equivalent rating of R-20 for a single layer.

So, the obvious question is does this stuff really work and would I be a fool to use only radiant barrier throughout the house and in the attic? According to the seller, 2 layers of radiant barrier is equivalent to R-53. eBay auction number 220119795834 Seller: thermalkool

I was thinking of doing an experiment with a few thousand SF of barrier. I'd staple one layer of barrier to the underside of the roof rafters, and leave another area exposed. Take temps readings to see how much heat gets by the barrier.

I've also seen paint coatings that claim to be radiant barriers, but my BS-meter is high on that.

What says the gallery?
jurgen

[Por_sha911]

Read this

[dad911]

If you are building with permits and inspections, I would doubt the building inspectors will accept an ebay ad as documentation.

Roof/attic systems also require ventilation. I would think that applying this product to the underside of the rafters as suggested will lead to premature failure of the rafters and roof shingles.

[Porsche-O-Phile]

Radiant barriers are legitimate methods of increasing envelope insulating value. I would be EXTREMELY skeptical of anything on ebay - it's a haven for scam artists and snake oil salesmen. As dad911 says, you'll also likely run into issues with documenting the energy code compliance based on a "well, so-and-so SAID so". They very often want manufacturer's cut sheets, etc. - something with a little bit more legitimacy.

Edit: different municipalities will respond differently to these and give different "credits" for using them. It's not necessarily a fixed number - talk with a building department official.

[island911]

Originally posted by turbo6bar
...

So, the obvious question is does this stuff really work and would I be a fool to use only radiant barrier throughout the house and in the attic? According to the seller, 2 layers of radiant barrier is equivalent to R-53.
....

BS-meter PEGGED.

One would have to have a huge radiant source for that to hold. (read: if your roof is on fire that may be true)

...and "2 layers" ?

[turbo6bar]

Alright, I'm back on the ground. Looks like radiant barriers are a good supplement to regular fiberglass. Thanks for the informative link, Por_sha911.

I want to get the best bang for the buck with a focus on energy conservation. That said, I don't want to go overboard. If fiberglass is best, so be it.

Would I be better off investigating blown cellulose or two part spray foam for the walls? Unfortunately, I'm stuck with the 2x4 exterior walls.

Ideally, I'd like to do the work myself. Getting the work past code is NO problem for me, and I obviously need to stick with recognized products/methods. Anything I do will be approved by the inspector beforehand.

[turbo6bar]

This is the candidate: ~4500 square feet on 7 acres.

[TyFenn]

Sounds like fun Turbo6! In a way I wish I could join ya...

I used to bang nails during the summers of my sophmore and junior years at Harvard. Those were the days.


Best of luck with the project - hope it works out.

[turbo6bar]

Thanks, TyFenn. I am really excited about the new challenge. My little brother and I have never tackled such a large project. Fortunately, we got it at a great price, so we can afford to pay for all the nice touches and upgrades over standard builder-grade. It's also great to have an uncle that owns a granite factory and who can get hardware flooring just above cost.

I guarantee you it will be a real gem. Jurgen

[Tobra]

Something that is surprisingly effective is a whole house fan. It is a large fan that pulls air into the house(have to open windows) and blows it into the attic, forcing the VERY hot air in the attic out the roof vents. Drops the attic temps an amazing amount, say from 140*F to 65*F. Last summer at my parent's house, there were days their A/C did not come on in their well shaded home until 5 in the evening, even in triple digit heat.

In the Sacramento area, we have something called the "Delta Breeze". In the evenings, the land radiates heat and warms the air above it up, causing it to rise. Pressure falls over land, pulling cool air in along the waterways of the Sacramento River Delta. Makes the temps drop pretty dramatically in the evenings, making such a fan very effective here.

[turbo6bar]

Wish I could, but the humidity in Tennessee is brutal. The added load from humidity control would negate some/most/all of the benefit of the whole house fans.

I'm going to bug a few local vendors this week re: spray foam insulation. The cost of the product is on par with fiberglass. The equipment cost is the real issue.

Basically, I'm trying to maximize the efficiency of the HVAC equipment installed by the last owner. It appears the units are plain 80% efficiency natural gas heat and no more than 12 SEER A/C. In an perfect world, it would have been a geothermal ground loop system (superb efficiency), but I just cannot justify the cost of ripping out thousands of dollars worth of brand new equipment to go with something more efficient. jurgen

[Tobra]

Plant some fast growing shade trees south of the house, has a large impact.