Insulation, Radiant and Vapor Barriers - radiant barrier

I am certainly intrigued about using rad. barrier especially to assist the cooling of our 2nd floor during the summer. The question I have, though, comes from an opinion of a contractor who said that RB works well but at the expense of overheating your roofing materials. Is that a concern?

My other ? is how to use RB in our application. Our house has a pitched roof with 5 foot knee walls in a converted attic space that has finished walls/ceiling. From the crawl space there is full access from the eaves to the knee wall but how would you install RB in the area from the knee wall up to the ridge of the roof? The rafters are 2x6, 24" on center. Also, with RB should there still be ceiling insulation between those 2x6 rafters for the sake of the winter heating season? (This is a home in Wisconsin)

Appreciate any input.

Thanks,

JA

Greetings, Jandrewnels

The contractors comment about the radiant barrier (RB) causing shingle failure is a perfect example of a little knowledge being dangerous. This belief comes about because the theory is that RB is reflecting the energy back to the sheathing. Actually the roof is radiating less energy to the insulation because the RB is absorbing only about 3% compared to about 90% plus for fiber glass. The roof material can only absorb so much as it is radiating the energy at the same rate as it absorbs it. I have measured the attic temp of a RB house on a 95 deg day and it was 106 degs.

Now to your problem. Retrofiting a 1 1/2 story is tough.
You can slide a HD type 2 material up the sloped sections and install on the bottom of the rafters in the access area. The section above the flat area (ceiling) has to be done through the ceiling, usually requiring a small boy(yes, it has been done). The other problem with these ceilings is the fact that the rafter on the sloped ceiling section is in direct contact with the sheathing and you you get a large, large quantity of heat energy through that section directly into the room. What I recommend for those areas, if possible, is to insulate that section from the interior side.

If you are limited to the access area, I would do that and then check http://www.radiancecomfort.com for a low emissivity paint. 1 1/2 story houses can be comfortable but its best to install a RB system during construction, as you found out.

By the way you can use this paint on the first floor walls too.

If you want to pursue this, contact me at my E-mail as it will require much more detail than what is possible here.

rbisys@juno.com

Thank you for considering my opinion.

Important facts can be found about the actual benefits of using RB insulations at the following web sites..

http://www.ornl.gov/roofs+walls/radiant/rb_05.html

http://www.ornl.gov/roofs+walls/insulation/ins_08.html

http://www.savenrg.com/1placemnt.htm

http://hem.dis.anl.gov/eehem/96/9609insulation.html

Good Luck

Jim

Greetings,

The websites that were posted are designed to discourage you from RBs.

In the two government sites they make very generalized comments about RBs not beiong as efficient. COMPARED TO WHAT. From a energy availability, if you have less energy to reflect then the RB is going to reflect the less energy available. It's still 97% efficient and FG is still about 10%. These are comments not consistant with the facts. The Government is not too thrilled about RBs. Wide spread use of Rbs could cost them loss tax revenues, BIG TIME.

On the 3rd website, no comment. I've read these guys before and I don't know where they come up with some of their stuff. Being in the RB business you think they would know better.

The 4 th site mentions RBs but then goes on to push bulk insulation. The house cut away looks like the one used in FG ads. Maybe?

Keep the faith, use the best, RBs.

Thank you for considering my opinion.