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Question about open cell foam + radiant barrier
Posted on 8/23/22 at 1:37 pm
Posted on 8/23/22 at 1:37 pm
My parents' home was constructed in 2005. It is 1.5 stories with walk in attic access on the second floor on both sides. The house was insulated originally with batts in the walls and living area ceilings. Their electric bill is pretty high and they have been looking into getting a radiant barrier stapled to the rafters in their attic. One of the installers recommended they insulate between the attic rafters with open cell foam, and add a radiant barrier top of that, across the underside/exposed side of the rafters.
It sounds great, but in reading online, it seems that a lot of people are concerned with moisture issues with open cell foam. Does anybody have any thoughts on the above suggestion? They are definitely going to do the radiant barrier, so the primary question is whether they should also do the open cell foam between the radiant barrier and the roof decking.
It sounds great, but in reading online, it seems that a lot of people are concerned with moisture issues with open cell foam. Does anybody have any thoughts on the above suggestion? They are definitely going to do the radiant barrier, so the primary question is whether they should also do the open cell foam between the radiant barrier and the roof decking.
3
Posted on 8/23/22 at 2:00 pm to bluemoons
I would think one would do one or the other but not both. A radiant barrier could be expected to lower attic temperature 15-20 F, encapsulation of the attic with open cell foam making it semi-conditioned space even more so.
But I would possibly suggest this. Perhaps the best route is to have an energy audit (blower door test, $350 to 400) to identify major areas of air infiltration in the house. Remember heat always moves to cold. If entry points of hot air from the attic into the conditioned living space below were sealed - plumbing, wiring, drywall plate joints, wall plates, etc then followed by increasing existing attic insulation from what I would assume to be R-30 to R-38/R-40 - that might give them the best bang for their buck, with significant reduction in energy bills. Then could always do a radiant barrier at a later date if it was warranted.
But I would possibly suggest this. Perhaps the best route is to have an energy audit (blower door test, $350 to 400) to identify major areas of air infiltration in the house. Remember heat always moves to cold. If entry points of hot air from the attic into the conditioned living space below were sealed - plumbing, wiring, drywall plate joints, wall plates, etc then followed by increasing existing attic insulation from what I would assume to be R-30 to R-38/R-40 - that might give them the best bang for their buck, with significant reduction in energy bills. Then could always do a radiant barrier at a later date if it was warranted.
Posted on 8/24/22 at 7:17 am to bluemoons
Some people say that installing foam on the underside can he harmful and cause premature failure of shingles. Some shingle manufacturers will void their material warranty because of this. I have heard arguments on both sides of this issue. My brother did this when he built his house and it makes a big difference. As far as the shingles go he did not notice any problems. Besides, you will get a hailstorm or hurricane help you with replacing your shingles anyway.
I do agree with the other poster about having the house tested for weak points so yu don’t waste your money.
I do agree with the other poster about having the house tested for weak points so yu don’t waste your money.
Posted on 8/24/22 at 9:11 am to Tomcat
quote:
Some people say that installing foam on the underside can he harmful and cause premature failure of shingles. Some shingle manufacturers will void their material warranty because of this. I have heard arguments on both sides of this issue. My brother did this when he built his house and it makes a big difference. As far as the shingles go he did not notice any problems. Besides, you will get a hailstorm or hurricane help you with replacing your shingles anyway.
I do agree with the other poster about having the house tested for weak points so yu don’t waste your money.
i have had open cell on last 2 houses and have had no problems with the shingles and its awesome
but OP, foam only works if you are willing to get rid of all attic openings. so no ridge cap, no whirly birds etc and you need to have the whole house sealed.
on top of that you will need to either have the duct work changed to be open return or you will need to put in a large dehumidifier.
so i would say no to the foam.
i would do the test that was talked about above and add the radiant barrier after what they found in the test is corrected.
Posted on 8/24/22 at 9:14 am to Tomcat
We did open cell foam on our attic rafters in 2014.We did not see any issues with the roof sheating when the roof was changed in 2019. When you do this you must make sure you are not introducing any moisture into the attic. We put dehumidifiers in the attic and vented all bathroom and kitchen blowers to the soffet.The temperature in my attic dropped 25 degrees.
Posted on 8/24/22 at 9:19 am to Deerhunter62
quote:
We did open cell foam on our attic rafters in 2014.We did not see any issues with the roof sheating when the roof was changed in 2019. When you do this you must make sure you are not introducing any moisture into the attic. We put dehumidifiers in the attic and vented all bathroom and kitchen blowers to the soffet.The temperature in my attic dropped 25 degrees.
yea my old house had zero issues when the shingles had to be changed after the hurricane.
and very imporant about the humidty in the attic. unless they are willing to make lots of changes, they should not go that route.
and yea my current attic is exactly the same temp as our 2nd story. it is a conditioned space and i had it made load bearing and floored it out and it is essentially an unfinished gameroom now
Posted on 8/24/22 at 9:23 am to lsu777
quote:
but OP, foam only works if you are willing to get rid of all attic openings. so no ridge cap, no whirly birds etc and you need to have the whole house sealed.
My understanding from speaking with both their a/c company and the insulator is that this only applies to closed cell foam, no?
Posted on 8/24/22 at 9:23 am to Tomcat
quote:
Some people say that installing foam on the underside can he harmful and cause premature failure of shingles. Some shingle manufacturers will void their material warranty because of this. I have heard arguments on both sides of this issue.
There has been an extensive study in FL that show even though shingles do get slightly hotter with a radiant barrier they do not decrease the service life of the roof, and vast majority of shingle manufacturers honor their shingle warranty with radiant barriers, but of course one should always double check first. That report is online and I’ve read it, but don’t have the link to it handy.
Posted on 8/24/22 at 9:30 am to CrawDude
quote:
There has been an extensive study in FL that show even though shingles do get slightly hotter with a radiant barrier they do not decrease the service life of the roof, and vast majority of shingle manufacturers honor their shingle warranty with radiant barriers, but of course one should always double check first. That report is online and I’ve read it, but don’t have the link to it handy.
it is the foam, not the radiant barrier, that causes shingle warranty issues.
Here is an article from a roofing company about it.
Posted on 8/24/22 at 9:55 am to bluemoons
quote:
My understanding from speaking with both their a/c company and the insulator is that this only applies to closed cell foam, no?
no. you are still creating a sealed envelope. closed cell/open cell doesnt matter at that point. we do open cell on roofs because if you have a leak you will be able to see it. closed cell it would just be trapped and rot away at the roof until collapse.
you still have to create the envelope and essentially form an ice chest with the house. and unless you built the house to be designed for foam (you didnt) or you are willing to spend lots of money redoing the roof, ac returns, bathroom vents etc than you shouldnt do foam.
get the test done and fix those issues, then add radiant barrier.
Posted on 8/24/22 at 10:35 am to notsince98
quote:
it is the foam, not the radiant barrier, that causes shingle warranty issues.
That’s true, but know radiant barrier do increase roof temperature and they have been questions as to whether they can shorten shingle life when I was looking into the subject. Short article by a radiant barrier vendor LINK
BTW, Here is summary Oak Ridge National Research Lab study on the efficacy of radiant barriers. LINK. Full study report LINK. Here is the link to the FL radiant barrier study LINK
This post was edited on 8/24/22 at 10:36 am
Posted on 8/24/22 at 10:37 am to CrawDude
quote:
That’s true, but know radiant barrier do increase roof temperature and they have been questions as to whether they can shorten shingle life when I was looking into the subject. Short article by a radiant barrier vendor
maybe but chances are you will have to change them out before they reach EOL anyways due to a storm
Posted on 8/24/22 at 10:41 am to lsu777
quote:
maybe but chances are you will have to change them out before they reach EOL anyways due to a storm
Yep - I believe you are right on that.
Posted on 8/24/22 at 11:17 am to CrawDude
quote:
Yep - I believe you are right on that.
my old house went 10+ years on the shingles and had no problems before the hurricane took it out and it was spray foamed.
Posted on 8/24/22 at 11:21 am to CrawDude
Thanks for that post. Based on that study, it seems that a rafter mounted radiant barrier is the way to go.
Does $7,000.00 installed for a 4000sqft under roof seem reasonable to y'all? I expected it would be a bit cheaper than that.
Does $7,000.00 installed for a 4000sqft under roof seem reasonable to y'all? I expected it would be a bit cheaper than that.
Posted on 8/24/22 at 12:05 pm to bluemoons
quote:
Thanks for that post. Based on that study, it seems that a rafter mounted radiant barrier is the way to go. Does $7,000.00 installed for a 4000sqft under roof seem reasonable to y'all? I expected it would be a bit cheaper than that.
Well does seem high to me but who knows in this business environment. When I was considering doing it, and still am, I figured I DYI it. I know there are some other posters on the H&G board that have DYI installed it.
You can buy the barrier material for about $1K for 4000 sq ft. LINK. Seems a high labor cost to cut and staple the product to the rafters - wonder if it would be cheaper if done in winter - cool, comfortable attic?
And it is one of the reasons I suggested looking into sealing the attic and other outside air entry points and adding additional attic insulation. I’d bet that would cost 1/2 as much and provide the same energy saving and comfort benefit.
Posted on 8/24/22 at 12:06 pm to bluemoons
$7000 sounds high. Not knowing what their electric bill runs in the summer it may take 15-20+ years to recoup the cost before seeing any savings.
Do the math using their actually cost for electricity and how many months per year that it is really hot. The government website, energy.com, says people can save 5 to 10 percent on cooling bills. Manufacturers say a person can save 17 percent.
A $500 per month electric bill saving 17% for 6 months per year = $510 per year. $7000 cost/$510 = 13.7 years to start saving money. If you use 10% savings its 23.3 years.
Do the math using their actually cost for electricity and how many months per year that it is really hot. The government website, energy.com, says people can save 5 to 10 percent on cooling bills. Manufacturers say a person can save 17 percent.
A $500 per month electric bill saving 17% for 6 months per year = $510 per year. $7000 cost/$510 = 13.7 years to start saving money. If you use 10% savings its 23.3 years.
Posted on 8/24/22 at 12:19 pm to bluemoons
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