Radiant barrier/ Insullation Delima
I am researching ways to improve our energy efficiency here and have decided that the most immediate need with the Texas heat is more insulation. I should mention that our A/C Ducts run through our attic which is about 4 feet high… in other words the temperature of our air is raised considerably by the outside heat.
To alleviate some of this I plan to increase the attic insulation to anywhere from R38 to R49 and in addition I’d like to go with a radiant barrier. Here is where I’m torn. The foil variety will give in (in theory that is) a 97% reflectivity witch is excellent, however it can’t be installed in an existing home all the way to the roof line and so you loose some of that 97% which matters considering the cost if greater than the spray on “paint” variety. The Heat-Block 75 seems to be the highest functioning of the spray on varieties it has a reflectivity of 75%, but because you can use a long narrow sprayer it will cover completely and all 75% will be retained. At least this is what I’ve been told.
As for insulation I wanted cellulose (the recycled variety… just trying to go as green as possible) but I have found that the cellulose contains Formaldehyde as a fire retardant and I’m really not keen on the idea of that being in our house especially being that I am very allergic to it… couple that with the fact that cellulose can mold and even with the retardants burn…and fiberglass is looking more appealing to me. There is a type called Jet Stream 73.3 which is not as irritating as the shaved fiberglass… and it is non-combustible, doesn’t support microbial growth and won’t rot mildew or deteriorate. So I’m thinking this is what we’ll go with… and I’m leaning more toward the R49 simply because we have an old 10SEER A/C and it is MUCH cheaper to insulate than it is to replace that unit(which will be replace for a small service fee by our home warranty when it finally gives up the ghost).
What is your experience with any of these products or types of products? I’d like to have some feedback from people who actually have them before I write a check. The ultimate goal is to reduce our bill and make our home more comfortable at the same time.
Replies
Someone has been giving you a line of bull.
I can't remember if the fire retardant is formald. but I do know that it is fireproof. Has a class a fire rating. The mold thing is a new one to me, never seen that one.
It sounds like someone that sells fiberglass insulation is in your head.
Search breaktime and you will find many discussions on cellulose vs. fiberglass.
I have seen cellulose burn three times in my life.And when it gets wet, it will support mold. The cells themselves are treated with borates against mold, I believe, but the way it holds onto water increases odds of mold in the surronding building materials.But the fact is, that for practical purposes, if it is going to get wet, there is another problem that needs to be dealt with, and while the chopped FG won't grow mold itself, in an attic, it will eventually contain dust that can feed mold too, so that arguement isn't very effective.My choice is FGBut I think that misses half his problem. He should be double checking to be sure he has enough venting, add insulating wrap to the ducting itself, and even consider foam to the underside of the sheathing to condition the entire attic space. I forget if cost was a major issue
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I agree ... never heard of formaldehyde being associated w/ cellulose. I believe that is definately incorrect (I say believe and definately ... I'm not an expert). I've worked in a cellulose factory (many years ago). They used powered chemicals ... no formaldehyde.
Don't know about supporting mold ... if you have moisture issues ... hmmm. I've always lived in arid country. Ask the manufacturer about applications in the humid south.
Just say no to radiant barriers. 75% 90% ... who cares what they are rated for in a lab ... shortly after install their reflectivity ends up being small due to dust. Search the discussions more for this. A lot of effort and expense forsomething that works ... in the lab.
Have you considered insulating the roof plane and enclosing the ducts in the conditioned space? Don't know if it is practical for you. New Buildings Institute and California Energy Commission did a lot of residential research on this. A HOT attic is tough on your A/C system ... you say R49 ... the more you insulate, the hotter the attic and the more stress it sees. Hence .... enclose the ducts in the conditioned space.
Take the money and instead of buying a radiant barrier ... use it somewhere useful.
"shortly after install their reflectivity ends up being small due to dust."Why would a radiant barrier installed on the bottom of a roof get dusty.Check the Flordia Solar Institute. I think that they have reports showing the value of radaint barriers in the deep south.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I think it will get dusty ... just because it faces downward doesn't mean it won't collect some dust. Granted the ratio of dust of a downward facing surface is significantly less than a horizontal surface facing up. It don't take much dust to obliterate much of the radiant benefit.
Maybe there is a best practices to ensure you maximize the radiant barrier benefit. I'm not aware of any ... and they are often sold as the end all. Throw out your insulation ... 1/16" radiant barrier gives you an 'effective' R-20.
Yeah, I'm a skeptic. I read a lot of reports about various products over the years. I've never kept up on the reading, so maybe there are new products that don't get dusty during or after construction that you can RELY on their performance. I personally wouldn't go out of my way to apply a barrier and I wouldn't count on it performing. My bias, admitedly.
The OP is in Texas so it WILL get dusty
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What!!!! There is dust in Texas?
And the humidity will glue the dust to everything.
Why would a radiant barrier installed on the bottom of a roof get dusty
Because most require an open airspace above them to actually achieve the stated insulation values
If a layer of foil in the roof assembly were really effective, we'd see renolds wrap either over the roof deck or under the rafters all over Texas.
I do like how the insulator is trying to sell OP blown-in FG, though. After all, if cellulose is getting moldy, most folks would notice the xmas ornaments and the like up there also moldering too.
I've seen mildew on rafters and deck down here where air stays damp, but it's generally dead by May from the heat.
Freaky today. Under the transluscent panel-roofed south-facing porch I get a report of 98º; In the shade on the north side, I show 94º; airport (5 miles away) is reporting 92º--attic thermometer shows a mild 128º, but we are at 50% overcast today.Occupational hazard of my occupation not being around (sorry Bubba)
"Because most require an open airspace above them to actually achieve the stated insulation values"No they have to "face" an air space.The confusing factor is calling them a RADIANT barrier. In many cases they are not acting as a reflector of radiant energy, but rather an poor emitter (low emisiviity) of radaint energy.For a roof the low emisivity side would go down (if it is a single sided product).For example a roof sheating with a radiant barrier on one side.The sun heats up the shingles which then conducts the heat to the sheathing. Because of the low emisivity surface it won't radiant that energy into the attic, but rather help heat up the shingles some more which will radiate the energy into space.FSEC used to have some school demostations project that showed this. But I could not quickly find it. But did find this.http://www.fsec.ucf.edu/en/publications/html/fsec-cr-1231-01/
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Edited 6/24/2008 8:38 pm by BillHartmann
For a roof the low emisivity side would go down
Still has a "snake oil" feel to it. Something about a layer or lamination of foil versus thousands of btuh per square for the better part of ten hours a day every day.
But, I know I am biased, too.Occupational hazard of my occupation not being around (sorry Bubba)
There is a formula for figuring the payback on adding insulation. I don't know what your projected costs for this are but as an example, if your cost is $1 per sq ft and if your heating costs come close to those in my area, you could be looking at a payback in excess of 125 years.
Going from R38 to R49 in any cost situation is going to be a very long payback period. If my figuring is correct, the R change you propose is less than 1% heat loss savings.
I never heard of th espray on radiant.
Assuming that you have it sprayed to the inside surface of the sheathing, it would do nothing to reflect heat to the exterior because reflective agents need an inch of air space immediately in front of them to do as stated. So a spray on th einside surface of the roof sheathing would reflect heat energy back at the interior of the house and prevent it from radiating out at night.
What is your venting situation? Soffits and ridge or cap vents need to balance and in your area should equal one sq Ft of vent for each 100 S ft of living area.
general rule of thumb is three years payback for adding decent insulation, but that is a declining curve, so since you have plenty already, adding more could take 6-10 years payback. Adding wrap to the ducting though can help the system work more effectively so the cooled air does not pick up so much attic heat on the way to the rooms.
I think the only time formaldehyde is added to cellulose is in some commercial glue on situations.
I hate the stuff myself and prefer chopped FG for blown in.
Spraying polyurethene foam to the sheathing is the best solution, but the most expensive
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There's a big misunderstanding about how radiant barriers applied to the bottom of a roof work. What they don't do is reflect heat coming from above. What they do is reduce the amount of heat radiated downward.It would be better to call them low-emissivity coatings. How well a material absorbs or radiates heat has a lot to do with its color. We know this about absorbtion if we've ever walked barefoot on an asphalt parking lot in the summer. The white lines are cool, the black asphalt unbearable. It works the other way in the same degree - dark colors radiate heat well, light colors radiate it poorly. Wood stoves are black because black bodies radiate heat best.Paint the underside of a roof deck silver (or even white), and it won't radiate the heat from the sun beating on the roofing anywhere nearly as efficiently. This is a proven way to reduce the heat load in an attic, particularly in a hot climate. See the piece I wrote in FHB's Tools and Materials department on this a couple of years back.Spray foam on the AC ducts, cellulose everywhere else. Better yet, foam the roof deck.Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein (or maybe Mark Twain)
"Get off your dead #### and on your dying feet." Mom
"Everything not forbidden is compulsory." T.H. White, The Once and Future King
ASTM and the DOE has defined a radaint barrier as having an emisivity of less than 10%."ASTM calls paint an interior radiation control coating (IRCC) if the IR emittance is 0.25 or less (ASTM product specification C 1321, "Standard Practice for Installation and Use of Interior Radiation Control Coating Systems in Building Systems")."The paint emmisiviites range from 22% to 90%.http://forums.taunton.com/tp-breaktime/messages?msg=105546.2
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I'd take 22%...
Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein (or maybe Mark Twain)
"Get off your dead #### and on your dying feet." Mom
"Everything not forbidden is compulsory." T.H. White, The Once and Future King
I see that you are getting around.Do oil stock analysis now.http://forums.taunton.com/tp-breaktime/messages?msg=106151.8.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I deny all knowledge.Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein (or maybe Mark Twain)
"Get off your dead #### and on your dying feet." Mom
"Everything not forbidden is compulsory." T.H. White, The Once and Future King
Actually, if you google my name, you'll get me, and this oil analyst, and some academic guy. I'm pretty sure we're different people.Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein (or maybe Mark Twain)
"Get off your dead #### and on your dying feet." Mom
"Everything not forbidden is compulsory." T.H. White, The Once and Future King
I'm skeptical, Andy, have you got anything to back that up?I just remember you had asked me for a write up on decking posts? I was traveling a lot then and forgot. Still want it?
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A lot of research I did a few years ago. I forget all the particulars, but it ended up a review piece in FHB. Could have been in Tools and Materials or What's the Difference. I'd guess it ran in 2006. The main focus was radiant barrier sheathing, but the paints came into play. Oak Ridge Labs had tested the sheathing, and found something like a potential 15% decrease in AC needs in a cooling climate.Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein (or maybe Mark Twain)
"Get off your dead #### and on your dying feet." Mom
"Everything not forbidden is compulsory." T.H. White, The Once and Future King
Thanks. Oak ridge is OK.but I'd want to review your article if I were spending my own money to try gaining that potential 15% to understand it better.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Oak Ridge ... very reputable. Very good.
Did they test it throughout a 'real world' scenario, though. W/out knowing the particulars, but knowing the lab a little, I would say they tested the potential in laboratory conditions to determine what potential a the material might have. If they tested it in real world conditions you should have 2 numbers ... Ideal/theoretical A/C reduction and true reduction.
I have no idea what the real world result would be ... my semi educated guess would be that the performance would be cut by at least half ... i.e. 7-8% savings rather than the 15% ... and not really knowing what kind of a radiant barrier we are specifically talking about. We also have no details of this test. Is this 15% savings on an entire house or just through the material it was applied to.
I feel there are too many variables to make judgements on based on a specific test or two. This is a relatively complex science with many real world variables that can significantly affect how it works.
I remain admitedly skeptical until I see evidence showing the practical real world performance. Has any one seen an e.g. ASHRAE or ASTM test related to this subject?
Well look who the singing pig dragged in...Greetings mate!
Hey Mongo. Hope all's well.Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein (or maybe Mark Twain)
"Get off your dead #### and on your dying feet." Mom
"Everything not forbidden is compulsory." T.H. White, The Once and Future King
I understand and appreciate your skepticism. Heck, I'm not even convinced about global warming, so skepticism is my middle name. Emissivity isn't as easy to grasp as reflectivity. Reflectivity is easy to measure intuitively, but that's not the case with emissivity.Here's the deciding factor in my book, at least as far as the radiant barrier sheathing goes. For most houses, it installs just the same as any other roof sheathing. And it might cost $400 more overall. I can't imagine the paint would be more than that, and a pleasant afternoon in the attic with an airless would take care of it.Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein (or maybe Mark Twain)
"Get off your dead #### and on your dying feet." Mom
"Everything not forbidden is compulsory." T.H. White, The Once and Future King
"a pleasant afternoon in the attic "LOL, after that, do you relax by cleaning out the septic tank?
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I never heard of th espray on radiant.
This time of year, getting to the end of the second, third, full month of a/c bills, itinerant/traveller types will go door to door with spray-on insulation products. Most are just silver paint. Some are just a lead-colored paint, too (not even forking over for metallic paint even).
Last year there were some folks selling "misting" systems to cool face brick veneer, and several bought them, too (and just paid more for water).
My fave was the über-swank subdivision that finally broke down last year and allowed residents to add solar screens to their houses. Just funny to watch them installing solar screens on a 10-15% door/window facade with the mandated charcoal architectural shingles on the 10/12 & 12/12 ptiched roof above . . . Occupational hazard of my occupation not being around (sorry Bubba)
If you are in the DFW area I would highly recommend Nico's Insulation.
(214) 560-6362 I think this is the right number.