Is Radiant Barrier Insulation a good, green option for attic insulation in Los Angeles?

Question

I bought a home in Los Angeles and only a small portion of the attic is insulated (with R-30 bat insulation). I'm looking for the most green and cost effective way to finish the insulation job. Is Radiant Barrier worth it - in both summer and winter? Or should I stick with fiberglass? Other options?

Answer 1

Without a doubt it works to keep the heat out. The big question is how well it works to keep the heat in during the colder months. I'm not an architect or builder, but to me it seems that in the winter you have heat escaping in all directions, while in the summer the heat is all comming downward, so a radiant barrier just in the attic wouldn't be as effective. I don't doubt that it will help, because it can block radiant heat in both directions, which is the primary source of heat. I just don't think it will be as effective. I am listing a few unbiased government websites that discuss heating and cooling savings of a radiant barrier. The first one takes into account the region, the amount of existing insulation, how the radiant barrier is applied, and many other facors you probably never thought of.

Answer 2

I was a bit skeptical myself till I installed it in the attic of my small house this past summer and the long and short of it is it does work.

It reduced the attic ceiling temp from 140 degrees to 94 on the hottest days.

Answer 3

With respect to the person above, a radiant decking barrier is a must in Texas.  It definitely keeps the heat from penetrating through into the home which saves you money in reduced energy costs.

When a home is being built, you can tell the difference when standing under a home that has the radiant barrier and one that doesn't.  There are two versions- the decking material that's used when the house is being built, and the spray-on kind for already constructed homes.

If you don't take my word for, take Tom Tynan's.

"The fact is you need a radiant barrier. The radiant barrier is the only form of insulation that keeps the heat from getting in the attic. Attic ventilators can only work after the heat enters. With a radiant barrier in your attic, it shouldn't be more than about 10 degrees hotter than the outside temperature in the afternoon. Once the sun goes down, the attic should reach the outside air temperature more quickly, and that's your ultimate goal--to have your attic temperature equal to that outside the house."

Answer 4

Look for hard evidence that radiant barrier insulation even works at all.

I've worked as an engineer in the Heating, Ventilation and Air Conditioning industry for 30 years and the stuff is not mentioned in the heating/cooling load calculation manuals at all.  That makes me wonder.

A conservative approach would be to have a well ventilated attic and R-30 bats.

Answer 5

In LA you don't have a problem with cold. It works for heat when used correctly. Just finished building a house in Northern Cal with silver wrapping. House itself has extra insulation properties, but we have vaulted ceilings, so the barrier went on the roof instead of between attic and house. Without any heating or cooling yet, the "attic" between the roof sheathing and the R30 ceiling insulation was 5-10 degrees cooler this summer than outside. It worked best when temperatures were in 90's. After 100, the difference decreased.

For best results, the whole house has to be wrapped, especially walls exposed to the sun. It's possible it works better on the roof sheathing than in the ceiling, I don't know.

You do still need regular fiberglass batts as far as I know, the radiant barrier isn't rated yet as a stand-alone insulation. It's categorized as something else.

And if you aren't at least covering your whole roof with the radiant (including attic walls) you're not really accomplishing anything with it, and should just stick with fiberglass.

If you want to be more green, you can use recycled denim or paper insulation instead of fiberglass. It's a blow-in insulation. R value is determined by thickness of fill. You can search them online.