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We live in upstate SC in a home built in 2006. The exterior is vinyl siding with a small amount of face brick in front for aesthetic purposes only. The brick is not structural as far as I can determine. The entire house is one story on a slab except for the bonus room over the attached garage. The floor area is in the range of 1,500 sq ft not incl the garage. The roof is 12:12 pitch. The HVAC consists of a Trane heat pump outside and interior air handling unit, etc., in the attic. This was installed in 2010 when we bought the house. (The original HVAC equipment had been vandalized during the foreclosure period before we bought the home.) All the ducts are in the attic and are all wrapped with several inches of insulation. The ceiling insulation is blown in and it appears to have settled to about half the depth of the 10" ceiling joists in much of the attic.

In cold weather, when it's <30 deg or so outside, like it has been lately [we moved down here to escape this nonsense! :furious: ] the heat pump can't keep up, even with the aux electric heat strips in the duct work. Last week, when we crawled out from beneath five blankets it was 55 deg in the living room! :eek:

We're inviting some insulation contractors to come in and give us some ideas. One has suggested spray foaming the underside of the attic roof. Of course, he makes it sound like the greatest thing since canned beer! He called it an "investment" but he said it'd keep the attic much cooler in summer and warmer in winter, and I believe him. I just don't know how much "credit" to give the idea!

Our question now is: is it feasible to expect that doing this would eventually save enough in HVAC electric bills that it'd pay off in some reasonable length of time? I don't know what reasonable would mean. I doubt it'd pay itself off in less than 10 years? I'm not sure if I'd consider a 10-year payback period reasonable or not; I might. But when it's 55 in the living room something's gotta be done!

What should we expect, if we decide to do this? What issues should we think about, pro and con?
 

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The short answer is no.

The attic in your home is ventilated and you would need to covert to an unventilated design which would require closing up the soffits, ridge vent, and spraying the entire underside of the roof with R-38 and then covering it with a code approved intumescent.

You would be better served to air seal and insulate the attic floor and slow conditioned air loss that way.

Another point worth mentioning is that Heat pumps can only keep up before they go into Aux mode with a small enough temperature differential.
 

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I agree, moving the thermal boundary to the roof deck wouldn't be the best move. In addition to all of the items WoW discussed, you'd also have to remove all of the insulation you currently have on the attic floor. Air sealing is far and away the best thing you can do first. Air moving from the attic into the house needs to be stopped and then add insulation after sealing.
 

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Discussion Starter #4
OK so what else could I do

OK, so the 2nd contractor who showed up, after I posted the OP in this thread, said he does not recommend spray on stuff; he recommends radiant barrier stapled to the undersides of the rafters, leaving the soffit vents open so air can move up from there, between the radiant barrier and the underside of the roof, to the ridge vent. He said this would not "cook the shingles" and would allow air flow inside the attic, upward where it should be, and would still reduce the interior temp in the summer and keep the attic from getting too cold in winter also.

Your thoughts, please, one and all...
 

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Pulling the duct insulation and air sealing them with mastic/mesh tape/insulation/VB would be first, if not done already. Code for your Zone 3 is R-30, not 38; http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=South Carolina

You are in same Zone 3 as Dallas, TX, R-5 would control your condensation and minimum of 1" SPF will satisfy your air barrier, Fig.5; http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation?full_view=1

To meet Code minimum with the foamboard, you require R-5 plus fibrous batt to R-30; chart; http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_8_sec006.htm

Check with your local AHJ on the ignition barrier requirements; http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&ved=0CDsQFjAD&url=http://www.sprayfoam.org/files/docs/2012/Day2%20Session%201%20-%20Ignition%20and%20Thermal%20Barriers%20Sorting%20Through%20the%20Confusion.pdf&ei=b8bZUoeLG86JogSBk4HYBA&usg=AFQjCNFNhMEfX3JdWJ9HNMyL-FDd6c8HDQ&bvm=bv.59568121,d.cGU&cad=rja

Cons; lose 10% shingle life; http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation?full_view=1

Gary
 

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I'm a proponent of radiant barriers in the attic for homes in the south, but the installation detail that he's offering won't do a thing for you during the cold winter.

Additionally, spraying the roof decking with insulating foam won't "cook the shingles". The fact that he says something so dumb makes me question his qualifications to be doing work in this field.
 

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Spray foaming the underside of a roof will increase shingle temperatures and reduce their life span. He's not wrong.
 

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Spray foaming the underside of a roof will increase shingle temperatures and reduce their life span. He's not wrong.
I will have to disagree with you here.

An overwhelming majority (depending on the pitch it can be as high as +99%) of the cooling happens to the outside of the roof.

Orientation, shingle color, and exposure have much more to do with peak shingle temperature than does spray foaming.

Example...a lower (4:12) slope roof that is black and south facing in Florida will have a much higher peak temperature than will a higher pitch roof in a lighter color without the southern exposure.

Which roof is going to burn up?

They are also moving away from vented attic in some of the warmer and more humid regions as well.
 

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Radiant barrier won't help with heating your house.

In my area, most heat pumps can keep a house at 70 without using aux heat when its 30 outside. Sounds like there is a problem with your heat pump, and aux heat.
 

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Spray foaming the underside of a roof will increase shingle temperatures and reduce their life span. He's not wrong.
He is wrong to use the expression "cook the shingles" since it is not factual. Gary in WA posted some links to great articles that provide factual data concerning the issue of damaging the roof by moving the thermal boundary. They're well worth reading.

Joe Lstiburek is probably the most respected person in the field of building science and here's some of what he has to say on the subject.

http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation


"Effect on Shingle Life"
In general, shingles installed on unvented attic assemblies operate at a slightly higher temperature. This has impacts on the durability of roof assemblies. A 2 or 3 degree F. rise in average temperature is typical for asphalt shingles and a corresponding 10 degree F. rise in average temperature for sheathing (Parker & Sherwin, 1998; Rudd & Lstiburek, 1998; TenWode & Rose, 1999).

All other things being equal, applying the Arrhenius equation (Cash et.al, 2005), a 10 percent reduction in useful service life should be expected. This is comparable to the effect of the installation of radiant barriers. What is more significant to note is that the color of shingles and roof orientation have a more profound effect on the durability of shingles than the choice of venting or not venting (Rose, 1991) – double or triple the effect of venting/non venting."

Even if the additional heat degrades the shingle some (10% - 15% being the educated guess) it may well be worth it for homeowners in hot and humid climates. It should be factored into the consideration of course.

http://www.asifoam.com/library/Joseph_Lstiburek_-unvented_attics,__7-11-99.pdf

While I don't disagree that spraying foam insulation on the underside of the roof decking increases the temperature of the roof, and therefore COULD have a small negative effect on the life of the shingles, it doesn't warrant scaring people by telling them that their shingles will be cooked. Ironically, the additional heat caused by foaming the roof is actually about the same as applying a radiant barrier, which the second salesman was promoting. Would he say his radiant barrier would "cook the shingles"? If not, he was being dishonest and that's what I take issue with.

Consumers should do exactly what the OP is doing, which is gather the data and make an informed decision. What they don't need is a salesperson trying to sway them by uninformed scare tactics that take a small amount of truth and a large amount of exaggeration.

Lastly, the OP was complaining of a cold house. The second salesperson offered a radiant barrier, which does nothing to deal with the immediate problem that the homeowner is trying to solve.
 

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Get your R-30 insulation in and forget the radiant; http://usatoday30.usatoday.com/USCP/PNI/Features/2012-07-07-PNI0706hom-rosiePNIBrd_ST_U.htm

Shingle temp; http://seattlewindowsanddoors.com/2013/07/03/insulated-rooflines-and-shingle-temperatures/

Moving the thermal/air barrier to the rafters is perfect for your location. You made the top3; http://www.buildingscience.com/documents/published-articles/pa-built-wrong-from-start/view?topic=doctypes/published-articles

Problem in the summer with letting all the moist outside warm air in against the cold AC unit/ducts, plus the air loss of those ducts.

Gary
 

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While I agree that radiant barriers are statistically insignificant after R-19 and certainly R-30...where they might pay dividends is keeping some of the additional heat out of the ductwork that is horribly insulated.
But if duct work is poorly insulated, wouldn't he just insulate it properly (at least to minimum code requirements) before spending money on radiant foil? The heat gain from radiant energy is minimal; http://www.ecobuildingpulse.com/energy-efficient-design/a-close-look-at-common-energy-claims_8.aspx

Bubble wrap radiant on ducts;http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/29497/The-Foil-Faced-Bubble-Wrap-Sham-Understanding-Radiant-Barriers

Gary
 

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But if duct work is poorly insulated, wouldn't he just insulate it properly (at least to minimum code requirements) before spending money on radiant foil? The heat gain from radiant energy is minimal; http://www.ecobuildingpulse.com/energy-efficient-design/a-close-look-at-common-energy-claims_8.aspx

Bubble wrap radiant on ducts;http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/29497/The-Foil-Faced-Bubble-Wrap-Sham-Understanding-Radiant-Barriers

Gary
I agree.

Fix the issue at its source.
 

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I rarely weigh in on these conversations because there are posters here far more knowledgeable than I am, but just my 2c worth.

Our house was cold, ridiculously cold when we bought it, oil furnace + fireplace and the last guy still put a woodburning stove in the LR cold.

I have really been concentrating on basic stuff, air sealing and insulation, FG in the attic, foamboard @ rim joists, etc., overall way less than a grand in materials so far but this goddawful-polar vortex winter so far has tested it all and it has exceeded expectations, so I know a lot can be done with a few $$$ and a lot of time and swearing.

The single best thing I did was get one of these:

http://www.harborfreight.com/non-contact-infrared-thermometer-with-laser-targeting-69465-8905.html



Now I know the pros here laugh off cheap tools solutions but hey, I'm working with what I have. I have located serious air leaks and cold spots that I would never have found otherwise, and have a far better understanding of exactly how the heat is working in this house. You can spend a lot of money if you don't know exactly what is going on with your house, and you cannot assume it is exactly like the nextdoor neighbor's just because they were all built together. Figure out why it's cold and then act on it.
 

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Discussion Starter #17 (Edited)
We have met the enemy and he is us!

Thanks, guys, for the good advice. Esp the part about maybe there's a problem with the HVAC unit in the first place.

Turns out, there is! We had it checked out today. The control panel is receiving a "start" signal for the aux heat strips when the heat pump itself can't keep up (the outside temp got down below 10 deg last week, and we're in SC :censored: ) but the heat strip isn't starting. So the heat pump by itself was all we've had for the past two weeks or so, at least.

That's good news and bad news, I guess. The bad news is, it's broken. The good news is: it's covered by our warranty and the control panel will be replaced free; once it works right, the entire system IS sized properly, the ducts ARE well insulated, the attic IS ventilated as it should be, there ARE no outside-inside air passageways we need to be significantly worried about, and best of all, I guess, we HAVEN'T been sucking down extra kwhrs these past 2 weeks after all! Course, we've been freezing, but now at least we know why and what to do about it!

And it puts the entire issue of what kind of additional insulation to consider in the attic in a whole new light, too. We did determine that our existing blown-in insulation has settled to a point where we may not have much more than about the effect of R11, so we'll probably get more blown in, but maybe we'll stop at that point and see how we feel, now that we know the HVAC isn't working as it should.

Thanks again, all of you!

Tom in SC

ps. How many of you are old enough to recognize the title I used for this message? How many of you are willing to ADMIT you're old enough to recognize it!? :thumbup:
 

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We have met the enemy and he is us!

We have met the enemy and he is us!


Thanks, guys, for the good advice. Esp the part about maybe there's a problem with the HVAC unit in the first place.

Turns out, there is! We had it checked out today. The control panel is receiving a "start" signal for the aux heat strips when the heat pump itself can't keep up (the outside temp got down below 10 deg last week, and we're in SC :censored: ) but the heat strip isn't starting. So the heat pump by itself was all we've had for the past two weeks or so, at least.

That's good news and bad news, I guess. The bad news is, it's broken. The good news is: it's covered by our warranty and the control panel will be replaced free; once it works right, the entire system IS sized properly, the ducts ARE well insulated, the attic IS ventilated as it should be, there ARE no outside-inside air passageways we need to be significantly worried about, and best of all, I guess, we HAVEN'T been sucking down extra kwhrs these past 2 weeks after all! Course, we've been freezing, but now at least we know why and what to do about it!

And it puts the entire issue of what kind of additional insulation to consider in the attic in a whole new light, too. We did determine that our existing blown-in insulation has settled to a point where we may not have much more than about the effect of R11, so we'll probably get more blown in, but maybe we'll stop at that point and see how we feel, now that we know the HVAC isn't working as it should.

Thanks again, all of you!

Tom in SC

ps. I tried to call this reply We have met the enemy and he is us! but I'm not sure it shows up that way on the forum. Assuming it does, how many of you are old enough to recognize the title I used for this message? How many of you are willing to ADMIT you're old enough to recognize it!? :thumbup:
 
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