Radient Barrier

[PhenomeNhan]

Has anyone used a product like AtticFoil (www.atticfoil.com) as a radiant barrier in your attic? It seems like a great product, but I am a little hesitant. Just wanted to get some feedback before I order some.

[arthurs]

We had ours sprayed in Nhan, but it works...big time. We experienced an immediate reduction in attic temp in the summer and in our electric bill....

[PhenomeNhan]

Thanks, Art & Mike. I did have a couple of other friends that had theirs painted several years ago, and it did help tremendously. The atticfoil site pointed out that the foil would be more effective than the paint, since a layer of air in between the foil and roof would help reflect the radiant energy more efficiently. They also pointed out that in certain situations, (metal roofing, for example,) adding the foil at between the metal roofing and roof backing would be even more effective.

Mike, can you explain what is meant by 'blown in'? I am thinking that is the insulation material on top of the ceilings? If so, that would help with the conductive heat and not the radiant heat. The site recommended that to be most effective, people would need to do both, and the foil is not a replacement for the insulation material.

Getting a new AC unit is pretty cost prohibitive. It's like $12K vs. $0.5K for the foil. I'm thinking that eventually, the AC will need to be replaced, and with the foil already in place, it will be even more effective. Maybe I can do a combo of paint (in places where I cannot reach easily) and foil. But I think that unreachable area maybe like 10% of the roof (at least for my dad's house). I do worry more about my house, since the roof's pitch is a lot higher and I would need to run the foil horizontally once I reach about 7 feet high.

That is, until you mentioned the stuff about dust build-up :D

[django1]

What I have read about the reflective foil is that it needs to have an airspace on the shiny side to be effective. It works just like when you use foil on food to keep it warm: it reflects heat back into the food.

"Keep in mind that it is very important to purchase a laminated reflective foil insulation product. This means the foil is comprised of one, two or even three layers of highly-reflective foil. These layers are often separated by thin layers of plastic mesh that creates a tiny air space between the layers of reflective foil. The multi-layered products are immune from any performance loss due to dust buildup. Dust will decrease the performance of single thickness reflective foils"

[PhenomeNhan]

What I have read about the reflective foil is that it needs to have an airspace on the shiny side to be effective. It works just like when you use foil on food to keep it warm: it reflects heat back into the food.

"Keep in mind that it is very important to purchase a laminated reflective foil insulation product. This means the foil is comprised of one, two or even three layers of highly-reflective foil. These layers are often separated by thin layers of plastic mesh that creates a tiny air space between the layers of reflective foil. The multi-layered products are immune from any performance loss due to dust buildup. Dust will decrease the performance of single thickness reflective foils"

Thanks, Django. The product I'm looking at has the reflective foil on both sides. It will be stappled to the roof's rafter, so there will be about 6" of air space between the foil and roof.

I think the specs here meets most of what you quoted above:

http://www.atticfoil.com/radiant-barrier.htm

I can't find info about how many layers of plastic mesh the product has.

[adamdivine]

I installed the reflective barrier in my attic last year. It is the kind that is reflective on both sides with an airspace in-between (think foil covered bubble wrap). I also added an attic fan to add some air circulation. I haven't been through a summer with it yet, but over the winter the house kept in the heat much better than the year before. My new upstairs bathroom has the reflective barrier on its two exterior walls and it keeps heat in extremely well. This should be indicative of its ability to keep the heat out as well. Just make sure there is an airspace between the reflective layer and the sheetrock or plaster in your house (as little as 1/2" will suffice) to prevent condensation buildup between those layers. If you are going to lay it on the ceiling joists, leave a gap (few inches) at each end to allow the condensation to escape.

[PhenomeNhan]

I installed the reflective barrier in my attic last year. It is the kind that is reflective on both sides with an airspace in-between (think foil covered bubble wrap). I also added an attic fan to add some air circulation. I haven't been through a summer with it yet, but over the winter the house kept in the heat much better than the year before. My new upstairs bathroom has the reflective barrier on its two exterior walls and it keeps heat in extremely well. This should be indicative of its ability to keep the heat out as well. Just make sure there is an airspace between the reflective layer and the sheetrock or plaster in your house (as little as 1/2" will suffice) to prevent condensation buildup between those layers. If you are going to lay it on the ceiling joists, leave a gap (few inches) at each end to allow the condensation to escape.

Thanks for the info, Adam. I will probably give this a shot after doing some more reading in preparation.

[dvenardos]

I do worry more about my house, since the roof's pitch is a lot higher and I would need to run the foil horizontally once I reach about 7 feet high.

Hopefully the experts (I am certainly not one) will chime in here, but with that kind of attic space it seems like it would be a lot cheaper and more effective to go with more insulation. Rent a blower and blow-in insulation (fiberglass or cellulose) on top of your existing insulation. The blow-in will fill gaps that may be exposed by rolled insulation.

[PhenomeNhan]

Hopefully the experts (I am certainly not one) will chime in here, but with that kind of attic space it seems like it would be a lot cheaper and more effective to go with more insulation. Rent a blower and blow-in insulation (fiberglass or cellulose) on top of your existing insulation. The blow-in will fill gaps that may be exposed by rolled insulation.

I will indeed add more insulation where needed (plenty up there already). However, that insulation will not keep the radiant energy out of the attic (its good for reducing conductive and to an extent convective heat away from the ceiling and walls). Additionally, the insulation won't do anything to protect the AC vents that are in the attic either (and most are above the insulation itself). So with the ways homes are built here, keeping radiant energy out of the attic is the first defense.

[dvenardos]

Interesting, I have no idea what AC vents in the attic are. Clearly out of my league... :confused:

I will indeed add more insulation where needed (plenty up there already). However, that insulation will not keep the radiant energy out of the attic (its good for reducing conductive and to an extent convective heat away from the ceiling and walls). Additionally, the insulation won't do anything to protect the AC vents that are in the attic either (and most are above the insulation itself). So with the ways homes are built here, keeping radiant energy out of the attic is the first defense.

[PhenomeNhan]

Call it what you want but heat is heat. All heat in the attic is radiant because it essentially radiates through your roof from the sun beaming on the top surface. If it's 130 deg in the attic it's just stinkin hot up there and the amt of insulation does make a diff no matter what type of heat you call it. You are getting wrapped up in all the fancy terms the RB companies want to call it to sell you product. If your AC ducts (not vents) are not mostly under the insulation then you don't have enough insulation. Effectively lowering your electric bills is a product of all systems working together, not just one. Insulation, attic ventilation, AC System. Ventilation is the most effective defense to keep the heat out of the attic. Heated air naturally rises so why not use that free energy to your benefit.

RB falls under insulation but you should also pay attention to the others as well. Do you have recessed can lights in your ceilings? Those are horrible leaks of interior air space and can be sealed to reduce loss. Checked for air leaks where the AC ducts connect to the AC Plenum box and be sure to seal where the vent outlets come into the rooms below? That's another culprit for major leaks and easy to test.

Thanks, Mike. I did mean ducts, and not vents. I do see quite a bit of those ducts above the insulation making their way from the AC unit to their final destinations. I didn't have any control over how that was done, since I'm the second owner of this house. When I do get the unit replaced, then I can ask them to route the ducts in a more efficient manner. Until then, I see that spending $500 on a foil radiant barrier will give me the best bang for the buck. That's why I'm asking here if anyone has experience with this product and does it work to reduce the temperature of the attic space. I've experienced a huge reduction in temperature with the aluminum paint barrier (and Art's also attested to his experience with it). This is with all things held constant (no changes made to ventilation or the amount of blown-in insulation that sits on the ceilings). The paint works....just wondering if the foil works, as well. I'm doing DIY, so cost of labor would be negated in this case (vs. lesser cost of labor for the spray method).

BTW, I'm not making up the terms, and neither are those companies :D Heat is definitely transferred in 3 different manners. If I can reduce the primary transmission, then that would reduce the heat issue tremendously. Like you said, the sun radiates thru the roof and into the attic. So if I can deflect that heat, wouldn't the temperature in my attic automatically be lower? Note that the company I linked to does talk about proper ventilation and blown-in insulation, in addition to the foil radiant barrier. Most of that made sense to me.

Hence, I don't disagree with your assessments about the ventilation of the attic and of the leaks (and will take measures to test/seal wherever I can). I had added an electric fan several years ago. It has since died, so I'm planning to replace it with a solar one.

[PhenomeNhan]

Interesting, I have no idea what AC vents in the attic are. Clearly out of my league... :confused:

My bad. As Mike pointed out, I meant ducts, not vents :D

[PhenomeNhan]

Nhan,

So you already have painted RB on the underside of your roof? IF that's the case why would a second be of much benefit? Is your RB going to cover all your attic? Even above your Living Room?

As far as the AC ducts having to be rerouted, if they are strung up high through the attic... you can just cut them loose and cover them with insulation. Having ac ducts up high is bad because they are sitting at a higher point which means hotter location.

If you had a powered attic fan you would need to put in at least 2-3 solar attic fans to make the same CMF otherwise you will be greatly reducing your ventilation and the heat reflected by the RB won't escape the attic. It needs the ventilation to carry it out of the attic.

Before you do this yourself. Get a few contractors to come out to your house to give bids and see what they rec for your attic situation. Free estimates and you will learn what's best for your situation. You have nothing to loose.

Good stuff, Mike. Thanks for the recommendation. I am still thinking about the solar ventilation fans (making sure at least one will fit in the space where the defective electrical vent fan is....probably a long shot).

I do not have painted RB underneath the roof...I have a couple of friends that did theirs several years ago. I was amazed by what a difference it made in their attic, as well as their garage (the door was also painted). With the foil, I was planning to use this method to cover the attic: http://www.atticfoil.com/flat-top-instruction.htm


That's a good idea with the ducts. I (obviously) don't know much about them, so I never even thought about cutting them down (will have a contractor here to assess before I do any cutting and such). It wasn't one of those things I thought about until I started reading the atticfoil.com site and their mention about heat loss with uninsulated ducts.

[HAL]

Nhan,
When we built the house 16years ago, we installed the foil paper backed style on the roof as it was installed. It has worked well all these years.

I now notice that some of it is starting to drop off the paper backing in some areas. Will have to see if it can be repaired in those places. If not, then new foil will be installed with the new shingles in a few years.

That, good insulation and a geothermal heat pump and life is good! :)

[PhenomeNhan]

Nhan,
When we built the house 16years ago, we installed the foil paper backed style on the roof as it was installed. It has worked well all these years.

I now notice that some of it is starting to drop off the paper backing in some areas. Will have to see if it can be repaired in those places. If not, then new foil will be installed with the new shingles in a few years.

That, good insulation and a geothermal heat pump and life is good! :)

Thanks for the info, Rich. I'll probably need to replace my shingles in a couple of years or so. I'll install the foil in my parents' house first and then do mine. Their roof/attic is not as challenging.

Here's to a cooler summer :)