painting roof white &/or radiant barrier insulation & insulating AC attic cooling ducts?

[niel]

to be sure we are on the same page here i was saying of placing the reflective material on top of the ceiling area rafters is not good because of the long span to the roof itself. standard insulation should not go on the ceiling rafters as another barrier could trap moisture and lead to all sorts of problems. it may work to a small degree in the roof rafters if the air gap is proper. 10 and 12in gaps are not proper. as was said already, this needs vented for each rafter space when its the roof rafters. if one is to go to that much trouble then throwing a small amount of insulation there with the vapor barrier facing up may work better, but one would still need to vent the attic space below due to humidity considerations. go get some advice from a professional if you can for your circumstance. ask him for an estimate too, but odds are it won't be acceptable for you to pay it and at least you would know what the best way is for you.

[Utana]

I finally re-found one of the information web sites that I looked up last fall. This Oak Ridge National Lab page has a nice map so you can see if radiant barriers are right for you. Incidentally, these are not the same as the shiny backing on fiberglass insulation. From what I recall reading, its better to use fiberglass without backing on it here in the south. I forget why, but there seems to be big differences in how you should best insulate the attic in the south vs. in the north.
http://www.ornl.gov/sci/ees/etsd/btric/RadiantBarrier/

Kelly

[Cariboocoot]

There are definitely differences in proper insulation practices between hot and cold climates.
The foil backing on fibreglass was intended to reflect heat back into a warm room in winter. It is not a vapour barrier at all. Nor is it contiguous so it doesn't work as a radiant barrier either. In fact it's pretty much been dropped for use up here too.

Got to use what works right for the particular job. And that's pretty much a universal truth.

[rollandelliott]

"This Oak Ridge National Lab page has a nice map"
I flipped through the 21 page long document, but didn't see anything about a map rating. I am in zone 3, what does that mean? I should get it?

[Utana]

From what I can tell, the map mostly relates to the information given in the first paragraph where it says: "Radiant barriers and interior radiation control coatings are designed to work in your attic to keep some of the heat from the sun away from your living space. For homes with air-conditioning duct work in the attic in the deep south (such as in Miami in Zone 1 or Austin in Zone 2), radiant barriers could reduce your utility bills by as much as $150 per year using average residential electricity prices. If you’re able to participate in one of the Time of Day rate plans, your savings can be even greater (almost $200 per year under the current Miami Time of Day rate plan). For milder climates, like those in Atlanta and Baltimore, annual energy savings will be about half those of their southern neighbors. In the northern climate zones, the savings drops further, going from about $40 to $10 per year as you go from Chicago to Fairbanks."

You are in the same zone as Atlanta (as am I), and according to the statement the cost savings will be about half that of zone 1 and 2, so as much as $75 a year or up to $100 a year if you participate in a time of day rate plan. The radiant barrier materials I am using will total about $60-$80 (space blankets, duct tape, and construction staples, and I think installing the barriers was worth it for me. If you want to use something more official than space blankets it may cost around $300-$600 for the install, depending on what material you use and how big your attic is, and may not be as worth it. Depends on if you think saving $75 or so a year is worth it. If you decide to use it, I would love to hear what you decide to use and if you get good results since we are in the same zone.

Kelly

[tonystewart]

I have seen a savings since radiant barrier was installed over a year ago in South Florida

[rollandelliott]

seems like it is most economical in the far southern USA if you have an HVaC system in your attic.
I think in order of importance it seems like:
1. good venting
2. insulate your duct work first
3. use barricade.

I'm guessing from reading that govt. study, the first two items are the most important.

[rollandelliott]

I'm almost done adding R15 insulation to all my attic duct work. This is the method I used
I bought brown packaging tape with the wet glue adhesive and I used this to take two 15" R15 rolled insulation lenghts and tape them side by side giving me a resulting piece that is 30" wide. I then put this over the exsisting R6 rated flex tube duct work that made a tent of insulation over it. Under neat the duct work is the ceiling insulation so there is no need to insulation underneath it. I used a staple gun to keep the insulation in place and minimize the gaps between any insulation. A cross section would look like this /o\
Where the "o" is the flex duct and the slashes are the two pieces of insulation.

I used more brown kraft tape to keep everything tight and for the bigger pieces of flex like the cold air return I wrapped completely around the tube.

Hopefully this will cut down on the AC a lot!

[rollandelliott]

www.roofcalc.com/

it has been down since 2011, but maybe one day it will come back online. seems like a good tool.

[rollandelliott]

It's August one of the hottest months of the year. I went up to my insulated attic ducts, took off the extra attic duct insullation I applied a month ago and the ducts were cool as a cucumber. That insulation is deffinetely doing its job! I've never ever felt a cool duct in any attic in my whole life. Just goes to show what good insulation does.