Please discuss which is better (insulation, cost,etc). If this has already been discussed I would appreciate if someone could link it. This is on a house that already has a new roof so the barrier attached directly to the decking is not an option. I read that foil attached to the rafters is the good but deteriorates fast. Thanks.

Everything I've read/heard says the actual foil works much better. Here's the best explination I've seen.

http://www.youtube.com/watch?v=E1IwS0_lpBc

And yes, I do realize this is from someone who sells the foil instead of the spray on. But it does make a lot of sense.

[This message has been edited by TravelAg2004 (edited 7/5/2011 1:57p).]

If you've already got a new roof, you really don't want to try to retrofit something on the inside of the attic. It's all snake oil.

Think about it this way -- the enemies of composite roofs (asphalt) are heat and U/V. By putting a radiant barrier on the inside of your roof, you're reflecting the UV and infrared back out through the roof that you just replaced. It'll dramatically reduce the life of the roof surface.

In a retrofit installation, you're much better just making sure your attic has excellent ventilation from the soffits to the peak that does not depend on an electrical fan, and that you have R60 or greater insulation in your attic.

Here is my take based on research and personal/professional experience.

Built in is great. But hard to retrofit. About 95-97% reflectivity.

The retrofit foil has much better specs than the best paint. My research showed 95% reflectivity vs about 75% for the best paint. The downside of the foil is that it is hard to put up if you have a complicated roof design. And the more complicated your roof design, the larger the amount of uncovered space you will have.

The paint is the least efficient, but easier to get full coverage on. So if your roof is complicated in design, I wonder if you would have a wash, or close to, between paint and foil based on the offset of the coverage versus effectiveness.

I had my Dad's condo done with the paint. Then he tracked the numbers on his attic versus a neighboring attic without paint. After trying to account for all variables as much as we could, we figured about a 15 degree improvement.

Based on my personal comparisons of the foil - more built in than retro - I figure it give you about a 30 degree reduction.

In the end, I have become less of a fan of the radiant barrier as a retrofit due to cost and ROI time. Even the paint is really pricey (it was cheap (the $500 minimum) in Dad's condo due to the small size.) I had my house quoted for grins several years ago and it was going to be around $2400 for the paint. I just did not feel the ROI was good enough.

I would definitely have built in done in new construction.

I bought some of the foil, and then tweaked a knee and never got it completely put up. The little bit I did was a HUGE PIA. Since then I upgraded the insulation, so I hesitate to mess with it and mess up the insulation install. If you or someone else is interested I would be willing to sell the foil rolls I have.

I have also often thought it might be easier to use the rigid foam insulation sheets they have a hardware stores that has the barrier on both side. If you followed the same installation instructions as the foil (leaving a gap at the bottom and the top for air flow) I would think it would be much easier to work with in the attic.

Whatever you decide, remember that no one step is a be-all end-all of efficiency. It is more about multiple parts working together. So with radiant barrier you need really good ventilation and still need really good insulation.

[This message has been edited by Absolute (edited 7/5/2011 4:49p).]

Seems like the only people who like the spray on reflective barriers are the people who sell it, although it is not too difficult to retrofit, although the material cost is close to that of the foil.

I read a DOE study that concluded the reflective barrier works as advertised in the very hot south, but not really that much better than fiberglass, so your money would be better spent on the fiberglass, which works better in the winter.

Aggie druggist did a write up last summer, and he said it was beneficial for the comfort factor, which the DOE did not take into consideration in their study.

I consider the stuff every year about this time, and decide to put it off until winter time, when it would be cool enough to do it, and invariably come up with a reason to stay out of the attic.

Something else to consider would be spray-in foam insulation on the underside of you roof, which would probably meet all the considerations, at a negligibly greater cost to having radiant barrier of batt insulation professionally installed.

Dubi, I am right there with you on both the thoughts of adding it and finding excuses not to do it.

The problem with the foam is that a sealed attic design requires adjustments to other systems of the home.

Don't get me wrong, I love the idea and I am impressed with the results I have seen in home designed for foam, but I am really uncomfortable with the retrofit idea. If you went that route, and it may be a good idea, definitely make sure the installer is very knowledgeable and get input from an HVAC pro too since having the foam completely changes the way the cooling system needs to be designed. Not to mention that if you have a regular 80% efficiency gas furnace (which most of us do around here anyway) it is not appropriate for a sealed attic.

The foam is not that much more expensive, but it adds a lot of variables and possible added cost on other things to be done right.

Another option I have seen a couple times is having the ductwork itself foamed. Completely seals the ductwork for leaks and really amps up the lousy R6 insulation value of common ductwork.

Not sure either option has a savings to investment ratio high enough to spend the money. If your ceiling is well insulated already it will probably take 10 plus years to pay itself off.

Just did the foil (someone search for me) and it dramatically reduced my attic temps.

You need a helper and a PLAN (most important part) and an electric staple gun (2nd most important part).

I had marbling on my roof rafters which means the temps got over 150°. The temp in my attic on the hottest days here in Houston with no rain is basically ambient now.

Total cost was <$400. I'll bet it will pay off before the summer is over. Also, the reduced shingle life is simply not true.

Haven't gotten 1-month bill yet but will report when I do. I'm betting it will be lower despite the intense heat.

Next project is insulation.

[This message has been edited by agracer (edited 7/5/2011 9:31p).]

Thanks for the great info. I may try putting the foil in myself but I will need to spend some planning time in the attic to come up with an efficient approach. Does anyone know how durable the foil is. Does it tear easy, will it sag after a while, etc. How long have you had it up.

Only had it for ~1-month. Don't have a full month electic bill yet.

You cannot tear the foil with your hands. In fact, I was able to pull on it and pull out staples from the rafters when I miss-fired.

The key, IMO, it to make a plan first, then get going. A helper is a HUGE plus with these projects. I did portions on my own and it was a pain just getting up the first few staples and making sure everything was mostly square.

Attic Foil

$ 400 is dirt cheap for the sheet radiant barrier, most people charge 1500 + depending on size of the house.

I am in the process of building my house.
Am looking at the foil backed plywood roof decking. Cost difference is about $2 per sheet.
From what I have researched, this should work.

I've had the foil in my attic for almost two years now. There were really too many variables to track to get an exact number on cost savings, but I will agree with the comfort factor. I noticed after finishing the install in September that the house felt cooler at the same temperatures. It also seemed that the AC would not kick on until later in the day. I did not time this however.

The key to having the foil work properly and keeping the shingles on the roof from getting too hot is adequate attic ventilation. You need to make sure you have plenty of soffits and some kind of ventilation at the top of the attic. See this website for a rough calculation to make sure you get enough ventilation http://www.dannylipford.com/adding-soffit-vents/. I need to work on the ventilation in my attic because I do not feel that I am keeping that attic as cool as I could otherwise.

AGENGRING, definitely pay the $2 extra to get the foil backed roof decking. It will be the easiest option in the long run if you want this done in your house. The DIY route can get very tedious. I have seen this be very effective in houses being built in my neighborhood.


Alpine if you go to www.atticfoil.com they will send you a free sample. The foil is pretty durable and strong and does not tear easily. I have not noticed any sagging since I installed it.

If you live in/near College Station, I will let you take a look at my attic. I did it myself over the July to September time frame. It was a long process because I only had the weekends and I could only work a few hours at a time because of the heat. Having a helper is definitely a timesaver. I did the whole thing myself and I was cutting a few lengths, installing them, and then having to come back down to cut more. The going up and down ended up being harder then the actual work in the attic.