Radiant Barrier (Dallas: university, costs, airplane)

[Korel]

Foil Good, Spray Bad (not as good).

We built a home in the Buffalo Creek Tour of Homes several years ago and installed the Cool-ply Radiant Barrier. We placed a small thermometer in our attic and hide one in the competitors attic who BTW, didn't use any radiant barrier. Mid July outdoor air was 100+. Mid afternoon sun brought our attic up to 110. The competition was 145. Similar size attic and comp roofing.

Back to lh_newbie's mention of the sealed attic system. This is the best yet. Forget the radiant barrier and we spray open cell Icynene on the bottom of the roof deck. Now our attics are mid 80s in mid summer. 72 in the house and 100+ on the roof surface. Fussing about the higher cost of foam? Go to the Energy Star Web Site (Federal Tax Credits for Energy Efficiency : ENERGY STAR) and see where you can qualify for a 30% tax credit up to $1,500.00 if you foam. That knocks a $5,000 invoice down to $3,500. Yea, you got to bankroll it until next tax time. Now consider the monthly savings. Some can tell you how much your electric bill could be and I have seen a 50% difference. Say you spend $400 a month in the summer and now your bill is $200. Makes more sense now, huh? It's not a matter of how much more foaming will cost you, it's a matter of how much more NOT FOAMING is gonna cost you. No I don't sell foam either.

A few years back we were involved in building Patio Homes in Addison off of Proton Drive and we thought we would try the foam. 2 identical homes a street apart facing the same directions. One was foamed the other was blown-in R-38 the ceilings and R-19 FG in the walls, like everybody does. We ran a comparison. The foamed house really did cost half as much to heat and cool over the other. And it was quieter. Addison Airport wasn't too far away and when a jet is departing, you can really hear it in the non-foamed house and not as loud in the foamed house. I wish we did some sound measurements then.

Anyway, this OP is 2 years old and some newer innovative stuff is out there.

[DPeter]

Korel,
Very interesting info. However, you first seem to recommend the cool-ply decking instead of foam with your title, "Foil Good, Spray Bad (not as good)" but then you extoll the virtues of the foamed house.

I will be doing a new home construction later this year. With all the differing opinions in this blog, it is hard to know just what to do. I think I like ih_newbie's recommendation of putting insulation (I assume this is normal fiberglass batting) directly under the roof decking. Seems to make sense to do whatever you can to keep the heat out of the attic in the first place. So then, why not use the cool-ply decking in conjunction with fiberglass batting insullation installed between the roof joists, under the decking. Then, for whatever heat still manages to get into the attic, use plenty of soffit and ridge vents to allow the heat a means to escape. Then, for good measure, add the conventional layer of fiberglass insulation on the attic flooring.

Anyone see any flaws in this for a new home construction?

BTW, the $1,500 energy credit is only for existing homes; not new construction. Darn.

[lh_newbie]

Originally Posted by DPeter

Korel,
Very interesting info. However, you first seem to recommend the cool-ply decking instead of foam with your title, "Foil Good, Spray Bad (not as good)" but then you extoll the virtues of the foamed house.

I will be doing a new home construction later this year. With all the differing opinions in this blog, it is hard to know just what to do. I think I like ih_newbie's recommendation of putting insulation (I assume this is normal fiberglass batting) directly under the roof decking. Seems to make sense to do whatever you can to keep the heat out of the attic in the first place. So then, why not use the cool-ply decking in conjunction with fiberglass batting insullation installed between the roof joists, under the decking. Then, for whatever heat still manages to get into the attic, use plenty of soffit and ridge vents to allow the heat a means to escape. Then, for good measure, add the conventional layer of fiberglass insulation on the attic flooring.

Anyone see any flaws in this for a new home construction?

BTW, the $1,500 energy credit is only for existing homes; not new construction. Darn.

Insulated roof decks do not use a ventilated attic. This method includes a sealed attic design, and the roof insulation is indeed spray urethane. The walls may be spray or fiberflass, but the roof is definitely spray. If you do fiberglass in the walls, make sure to use a house wrap to control air penetration. I personally prefer foamed walls also, as it provides a WAY better seal (no gaps, no air penetration, far more consistent insulation value). Foam is also a far superior insulation. In a standard 2x4 wall (3.5" cavity), you get R13 with fiberglass. In reality, it's less than that, but let's go with that. That's R3.7 per inch. Foam insulation is R6 per inch. Just putting 2" of insulation in that 3.5" cavity will get you the same insulation value and a perfect air seal (so it's equivalent to a house wrap AND fiberglass insulation).

If I were doing new construction, I would at minimum compare the costs of doing spray foam -vs- fiberglass+home wrap.

[NRGpro]

Any type of exhaust vent placed near the peak of a roof will benefit from soffet venting...except for a ridge vent.
The downward slope of the ridge vent acts like a thermal check valve trapping the hot air in the attic. Everyone in here would agree "hot air rises" right? Someone show me how hot air goes down...which is what is needed to allow hot, stagnant, bouyant air to flow out. I hear many retorts to this comment including: "the pressure in the attic forces the hot air out". There is no "pressure" in the attic. The only driving force to move air convectively is the differential density of the intake air (which is heavier and more dense than the attic air), which is pulled in by allowing a path for the hotter air to escape. A ridge vent cannot and will not do this. If you have any doubt, do what I did, get some Titanium Chloride chemical smoke and puff it up under the ridge vent around 2pm. You will soon become a believer as it just sits there.

Since I manufacture products that make attics hotter (radiant barrier), attic venting (adequate attic venting), has been our primary concern. That's one reason we are #1 on Google. Type in "attic venting" and you can see for yourself.

[NRGpro]

Yes, we built two identical 3700 sq foot homes side by side in 1986. One had R19 walls and R30 attic. One had NO insulation, only radiant barrier. Below are the results:
<li> RB home attic was never 3F over ambient
<li> As soon as the sun set, attic temp matched ambient
<li> Non RB home attic temp was 145F+ and over 130F at 10pm
<li> RB home had a family of 7 living in it and kept the a/c at 78f
<li> Non RB home had a couple who turned the tstat up to 86f when leaving
<li> Both homes had twice the attic venting code called for
<li> RB home used 35% less power and was more comfortable
<li> The RB house was much more comfortable all year. Test went for 1 year
<li> Downside: The RB house had road noise coming through the ceiling so before selling the house, we added a R25 blown cellulose to the attic which immediately made the attic hotter than it had ever been in the year of testing. INSULATION STORES HEAT!!!
<li> Dr. Byard Wood of ASU did the testing and documentation along with some graduate students.

Since this test, we have designed and built the Moderator cut:advertising link which uses no wall insulation, R19 blown cellulose in the attic (for sound), and covered by RBS Chips. Annual heating and cooling costs? $234 per year.
Show me any other type of construction that can achieve this. The second O.P.E.R.A. House we built was a Santa Fe style (notorious for being hot boxes), and uses $45 in August for cooling. There are now 7 O.P.E.R.A. Houses around the country and two commecial buildings using this building method. The last one using NO insulation of any kind and sits and bakes in the hot Arizona sun everyday.

Further, I would like to comment on something mentioned about radiant barriers being only used for hot climates. Ever look inside a Thermos bottle? Two layers of metalized glass facing each other with a vacuum in between to limit convection. Works for ice tea and hot coffee doesn't it? Why wouldn't it work in cold climates? Fact is, many people who comment in here voice opinions as fact which, as a scientist, can create problems and confuse people. I know for a fact what our Moderator cut:advertising link do in cold climates since we have been selling the product in the bitter cold Midwest and Canada. Over 40% reductions in fuel consumption and increased comfort are not exagerations or uncommon. We have also seen the elimination of ice dams in cold climates using this product since it keeps the heat in the house and doesn't melt the snow on the roof.

[loves2read]

the RB chips keep the temps inside the heated/cooled portion of the home vs allowing it to transfer to the attic I guess...

[lh_newbie]

Originally Posted by NRGpro

Yes, we built two identical 3700 sq foot homes side by side in 1986. One had R19 walls and R30 attic. One had NO insulation, only radiant barrier. Below are the results:
<li> RB home attic was never 3F over ambient
<li> As soon as the sun set, attic temp matched ambient
<li> Non RB home attic temp was 145F+ and over 130F at 10pm
<li> RB home had a family of 7 living in it and kept the a/c at 78f
<li> Non RB home had a couple who turned the tstat up to 86f when leaving
<li> Both homes had twice the attic venting code called for
<li> RB home used 35% less power and was more comfortable
<li> The RB house was much more comfortable all year. Test went for 1 year
<li> Downside: The RB house had road noise coming through the ceiling so before selling the house, we added a R25 blown cellulose to the attic which immediately made the attic hotter than it had ever been in the year of testing. INSULATION STORES HEAT!!!
<li> Dr. Byard Wood of ASU did the testing and documentation along with some graduate students.

Couple of items since you're using the statement that your a scientist to back up your claims: A sample size of one (two single instance tests) in uncontrolled circumstances in which are used totally differently (different thermostat settings, different number of people in them), by most scientists, should be considered an inadequate and inaccurate sample pool.

Furthermore, saying that because the RB home's attic temp after sundown was the same as ambient air and then the non-RB home's attic temp was higher, then drawing the conclusion that it's because insulation stores heat is a little weak. It's probably more accurate to conclude that the radiant barrier blocked the radiant heat from entering. Both attics have the ability to store thermal energy. One attic (the non-RB attic) simply didn't get loaded. The wood framing, the wood roof deck, and yes the insulation itself can all store thermal energy.

I'm just tossing up the BS card, your data is inconsistent and weak at best. Sorry, but I don't buy it. I've read a LOT of studies by DOE and NREL. They support what I'm aware of.

And for the record: Radiant barriers block radiant heat, not convective heat... but insulation does.

Forced heat creates convective heat in a home. Insulation slows the transfer of convective heat. Therefore, people use insulation in cold climates. In fact, in cold climates some people use south facing windows with little radiant barrier in cold climates to ALLOW the radiant heat to enter the home, get absorbed into the flooring (i.e. tile or something else that can store thermal energy), which is then released back into the home as the home's temp cools at night. There are many, many passive solar designs that use these principals.

While sample sizes of one are not considered accurate, I can state that when we increased our attic insulation in the home we live in now from practically nothing to roughly R49 (as per Dept of Energy recommendations), our natural gas consumption for the last two winters have averaged about 30% less and our energy usage has decreased by 10%. Same home, same thermostat settings (but obviously different years/weather patterns). I used heating degree days and cooling degree days to normalize the data to slightly increase the accuracy of that data. And yes, because we have no radiant barrier, our attic is pretty warm, but the now properly ventilated attic space stays substantially cooler during the day and cools quickly at night as the heat stored in the attic is vented.

Brian

[galore]

Originally Posted by NRGpro

Next: Radiant barriers placed up against your roof deck is the worst possible thing you can do aside from adding more insulation (sweaters in Dallas), in your attic.

A sweater in the Dallas summer on a body is a bad idea because the body produces heat by converting the energy stored in food ("burning calories") and the sweater inhibits the body's cooling mechanism. Almost none of your excess body heat can dissipate, if you wear a sweater in the heat.

It isn't a good example to argue against insulating an air conditioned house.

I suggest an experiment: Take two chilled cans of beverage, place one directly under the summer sun and wrap the other in a light colored sweater.
Check the temperature of both every 5 minutes and compare.

Or another experiment: Buy two bags of ice. Place one in directly under the summer sun but put the other one in a styrofoam cooler (=sweater in Dallas). Observe which one melts sooner.

[lh_newbie]

Originally Posted by NRGpro

Further, I would like to comment on something mentioned about radiant barriers being only used for hot climates. Ever look inside a Thermos bottle? Two layers of metalized glass facing each other with a vacuum in between to limit convection. Works for ice tea and hot coffee doesn't it? Why wouldn't it work in cold climates? Fact is, many people who comment in here voice opinions as fact which, as a scientist, can create problems and confuse people. I know for a fact what our RBS Chips do in cold climates since we have been selling the product in the bitter cold Midwest and Canada. Over 40% reductions in fuel consumption and increased comfort are not exagerations or uncommon. We have also seen the elimination of ice dams in cold climates using this product since it keeps the heat in the house and doesn't melt the snow on the roof.

I'd like to address this example as well. The two layers of metalized glass facing each other with a vacuum between... since heat requires some sort of matter to transfer heat (via convection), a vacuum is by definition a complete lack of molecules... therefore, nothing is present to allow for convection to happen.

The elimination of ice dams in cold climates is well documented by having the proper levels of insulation to stop heat from escaping the home. In fact, it's very common for folks to take a quick visual look at the roofs within a neighborhood to see which ones have snow on them and which ones don't. the ones with snow on them have better insulation; the ones without snow have less insulation (which allows heat to escape the home, enter the attic, warm the roof deck and melt the snow). This behavior is what causes ice dams. Radiant barriers will slow radiant heat from transferring. Insulation will slow convective heat from transferring. Homes are heated with convective heat.

There are companies working on vacuum insulated panels. This same technology is being developed for making more efficient fridge/freezers and ovens. The concept being employed in this is indeed the same being used in your vacuum based thermos bottle (vacuum providing insulation value).

I have a tendency to think that you have a vested interest in spreading this disinformation and incorrect correlation of data to support your business. I, on the other hand, am not selling anything.

As a scientist, I'm sure you'll appreciate 3rd party documents that explain these principals:

http://www.singleiteration.com/libra...ment.cfm?id=57

Brian

[Lakewooder]

Not sure my brain is wired correctly to get into this conversation but what about RB plywood decking with insulation on top / between the ceiling joists with the foil facing up?