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

rollandelliott

I want my house to stay cool in the summer and I have a few ideas.
I have a back sunroom/porch that gets baked hot in the summer. I added some blown cellulose insulation to the ceiling a couple of months ago but it still get pretty hot.
I read about radiant barriers here:
http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11680
I live near Charlotte, NC so it's fairly warm.
I added a power vent (mushroom shape) to the roof so a lot of the hot air is being drawn out.

Do you think the radiant foil barrier is worth it, even though I now have good insulation and good air flow?

Also in a different attic space I have a HVAC unit and all the cooling air flows through these attic ducts. Do you think wrapping another 4" of insulation round the thin walls of the cooling HVAC flex duct will be beneficial?

Lastly how about painting my asphalt shingle white? I have lots of left over white paint from a project and it wouldn't look that pretty, but I'd only paint a section that is not visible from the ground. Maybe that is a waste of time, but it seems like it would reduce the radiant energy from being absorbed a lot. I shiny mirror would work even better, but that would not be economical! LOL.

BB.

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

Insulating your ducts will be very helpful. Solar Guppy in the past has recommended when installing more ceiling insulation to just blow it right over the ducts.

Painting the roof may help, but I am not sure how well it will stick over time... You might end up with a bunch of white flecks of paint at the base of the house after a few years.

Most homes do not have enough attic venting--You might look around and see if you should add more (if you have enough inlet and outlets, you may not need the power venting).

If you add metalized reflective material--Be careful. A few years ago in Australia, their program and installers were not very careful and ended up electrifying the reflective material in some installations, causing electrocutions and fires (I guess by running nails/staples through wiring? Possibly covering over old knob and tube wiring, etc...).

I have never used the reflective insulation--So I cannot say one way or the other how well it works.

-Bill

niel

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

reflective insulation usually requires and air gap of between 1/2in and 1in and is usually facing the side to reflect the heat back into. this is almost always facing the interior to keep heat into the home as this deals with the radiant aspect of home heat loss. it would work in reverse i suppose, but to lay it on top of the present insulation won't do allot of good because of the air gap requirement.

i don't think a standard paint will work on roofing shingles, but in theory it would work to help cool the attic area by reflecting some of the heat away rather than absorbing it.

rollandelliott

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

yeah I'm guessing the white paint I have will flake off.
I saw thsi stuff
http://www.hytechsales.com/prod2000.html
about 60 cents a square foot for the primer and paint
not sure if it is worth it?

I can just go to lowes and get some aluminum colored roofing paint for about half the cost around 30 cents a foot.

I'm thinking that is what I do unless someone tells me this ceramic stuff is worth it at twice the cost?

rollandelliott

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

niel the recommendation for the reflective insulation is to staple it BETWEEN the roof rafters, thus radiating the heat back towards the source, the OSB wood and asphalt shingles. Basically trapping it there.

I guess I'm a little skeptical because I can't comprehend heat being radiated over 3 to 6 feet of air, through the insulation and into the home. Seems like with good air flow that heated up air would just escape, but then I read websites that say the reflective foil improves cooling by 10 to 20%.

The manufactures claims of 50% are just hype.

Dill

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

I installed the reflective insulation on the south facing roof of my cabin to help with the heat build up. The instructions stated to place it directly on the roof decking if in the southern US and insulate behind it, and if in the northern US, to place the insulation against the OSB and then cover the insulation with the reflective material. I just have it stapled to the rafters for now and it does seem to help.

Cariboocoot

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

I've used white elastomeric roof coating. Useless.
I've used radiant heat barrier. Only works under certain conditions.

Biggest improvement: better ventilation of attic space. Full eave inlet and ridge venting works best. Those "turbine" vents that spin in the wind are completely useless. Placing vents in the wrong locations can make it worse; air blows in one and out another and never moves air out of the attic.

You definitely do NOT want to seal up the space under the roof so that the heat is trapped there. This will degrade the roofing very quickly.

The only other thing to do (extreme measure) is to create shade outside the roof. Since it takes a long time to grow a tree, you can cover the roof with PV instead. I have known one place where they put metal roofing above the shingles raised on 4" legs.

rollandelliott

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

haha I was thinking of putting metal roofing raised over my asphalt shingles as well!!!! Not sure the return on investment would be that good unless I can get the metal cheap, perhaps a visit to my local metal scrap yard is in order?!?!

My attic is now pretty well vented. I have 6 metal box vent holes punched in the bottom of the roof line and two power vents at the top to draw in the air from below.

Stupid builders blocked all the roof soffit vents when they added the back porch. Before there was no ventilation, now there is a ton.

Utana

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

I did a bunch of research on this last fall and we installed radiant barriers as rollandelliott describes (directly to the rafters) in one section of our attic this winter. We had to wait until the dead of winter because any other time of year our attic was so hot we couldn't even enter it. This part of our attic is now much cooler, not cool by any streatch, but we can now enter it. The upper parts of our house don't heat up nearly as quickly as they used to. We are planning to do the rest of the attic starting this winter. We used those cheap space blankets for our radient barrier. Most of the expensive radiant barriers sold in hardware stores have that same reflective mylar on them as the space blankets. The expensive barriers usually also have some sort of backing, but I think it is the mylar part that does the biggest part of the job. We saved a lot of money using space blankets and are getting good results.

From what I've read the radiant barriers reflect radiant heat back up toward the outside of the house instead of allowing it to penetrate the rest of the house. The amount of air that gets hot between the radient barrier and the rafters should vent out through the roof vents.

From what I understood while researching radient barriers of this sort were not worth the effort in cooler climates in the north. This is primarily for radient sun energy that enters the house right through the roof. The radient barriers work much the same as those shiny mylar sun shields people put in their car windows in the summer time. And those can really do wonders to keep out the heat as well. I read a bit about the special paints as well, and seem to recall that they did help but were not as effective as the barriers.

You can also think of it as a radient space heater. Put a space blanket between you and one of those heaters and you won't get hot.

rollandelliott

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

Maybe after this falls' election I will ask to have some of those huge white pieces of plastic cardboard just to experiment and see if creating shade with them creates a cooler attic! They last about 3 or 4 years just long enough for the next election cycle. Ha ha.

niel

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

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

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

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

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

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

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

"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

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

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

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

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

rollandelliott

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

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

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

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

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

www.roofcalc.com/

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

rollandelliott

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

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.

mwegmannx

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

Hello. We have a AC vents exposed on our roof and it heats up a lot.
Is there a type of paint we could paint our roof venting so that it 1) reflectives the sun, 2) stays cooler?
Thanks,
- Michael

Cariboocoot wrote: »

I've used white elastomeric roof coating. Useless.
I've used radiant heat barrier. Only works under certain conditions.

Biggest improvement: better ventilation of attic space. Full eave inlet and ridge venting works best. Those "turbine" vents that spin in the wind are completely useless. Placing vents in the wrong locations can make it worse; air blows in one and out another and never moves air out of the attic.

You definitely do NOT want to seal up the space under the roof so that the heat is trapped there. This will degrade the roofing very quickly.

The only other thing to do (extreme measure) is to create shade outside the roof. Since it takes a long time to grow a tree, you can cover the roof with PV instead. I have known one place where they put metal roofing above the shingles raised on 4" legs.

inetdog

Re: painting roof white &/or radiant barrier insulation & insulating AC attic cooling du

mwegmannx wrote: »

Hello. We have a AC vents exposed on our roof and it heats up a lot.
Is there a type of paint we could paint our roof venting so that it 1) reflectives the sun, 2) stays cooler?
Thanks,
- Michael

Any paint you put on the ductwork (and I assume that is what you mean, since to us vents would just be releasing air to the outside or drawing outside air in) will have a minimal effect compared to actually insulating them in some way.
Any of the metallic reflective roof coatings might help in reducing the heat absorbed, but also look at the surrounding air temperature above a hot roof as a source of heat.
Any actual insulation will have to be protected against sunlight and weather, but you could put a waterproof (closed cell foam?) insulating layer on the outside of the duct and then cover that with additional sheet metal or foil wrap to shield it from the light.
We see more problems with ducts inside hot attics than exposed on rooftops these days.
I have seen setups where insulating board with a foil face is actually fastened to the inside surfaces of the ducts, but I do not know enough to say what the drawbacks of that might be. At a minimum it would have to be flameproof or at least not produce toxic smoke, especially if the same ducts are used for heating.