I am currently remodeling a kitchen and beefing up the insulation. Recently, I heard a discussion on public radio talking about the benefits of reflective insulation as a radiant barrier used on top of other insulation such as fiberglass batts. This is the type of material with a reflective surface backed by polyurethane bubbles backed by another reflective barrier. I can only fit R-19 in between the rafters and thought another insulation source would be warranted.
Does anyone have some experience with reflective insulation or can direct me to a resource that speaks directly to research or unbiased information on the material? Thanks.
Replies
I've used Thermax brand foil faced polyiso on the INSIDE, after installing FG batts, UNDER the sheetrock. This is something that Piffen has done too I think.
Helps with thermal bridging from the studs/rafters as much as increasing the R-value, and also acts as a vapor barrier if seams are taped. I suppose you could make a case for the foil acting as a radiant reflector as well.
It will effect the way that you fasten your sheetrock...easier to blow through the paper face on the rock and harder to set the depth on your screw gun, due to the compressing of the foam.
Or you could just spray (probably a contractor job) foam in there and be done with it.
Edited 11/30/2005 8:19 am ET by johnnyd
reflectivity is only of benefit if you have a couple inches airspace between the reflective surface and what you are insulating.-------------------------------------
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Where are you located? A radiant barrier is not always the best thing. For example in the north there's some quesiton as to whether or not its a good thing because it can cut down on the sun's ability to heat your house in the winter.
Radiant insulation and paint is one of the biggest "smoke and mirrors" in the energy efficiency world. The only time that it gives any R value worth considering is when you have no other insulation to use -period!!
One of NA's up and coming building scientist's siad something like this on a Greenlist post a few years back "We 've all known for years what true R value is about and we beat the foil back coming out of the 50-60's when it was sold by some for walls as the only insulation needed- a foil layer of vapour barrier facing the cavity (R value = 1.6). Now these foil bubble packs and radiant paint are keeping me ungainfully employed."
Save your $$$ and spend on some "real R". By the way, on another thread today, I mentioned my list of popular energy misconceptions that I've partially developed over the years. I counted them and have 83 things that hold a bit of truth that gets way over embellished (like foil bubble pack at R10-14) or are street level knowledge! (blown insulation will rot your house or you have to have a vapour barrier if you blow insulation into an old house)
Forgot to mention where to get info. The USDOE has section that you will get some answers at: US DOE Energy Efficiency and Renewable Energy (EERE) Home Page
Here's from a study from the Florida Solar Energy Research Center:
The reductions in the attic air temperatures after the RBS installation were pronounced. The AC reduction on the hottest days in which the home is occupied (no daytime thermostat set up) was 10-15%. Savings were considerably lower on cloudy or cooler days and week day periods when the AC is run less frequently during daytime hours. Using long-term periods in the summer of 1995, before and after the installation in the radiant barrier we estimated annual air conditioning energy use was reduced by about 5.5% (~430 kWh) from the installation.(2) However, the cost of the retrofit installation was high, approximately $1,100, as compared with the $400 that might be typical with new construction. With an estimated $32 annual savings, payback appears only attractive for new construction.
The $1100 would've been better spent on insulation or a new fridge or something>
Edited 11/30/2005 1:55 pm ET by experienced
Edited 11/30/2005 1:56 pm ET by experienced
Edited 11/30/2005 1:58 pm ET by experienced
Edited 11/30/2005 2:12 pm ET by experienced
Edited 11/30/2005 3:07 pm ET by experienced
(blown insulation will rot your house or you have to have a vapour barrier if you blow insulation into an old house)
At the risk of thread hijack.....can you elaborate?
What is the experience with cells in the south, with no VB? And just for fun, with no house wrap..... Although I'm not in the south, I'd like to know how global warming will affect insulation decisions I make today.....
Then there is the whole settling issue, and moist air coming in over the gap and condensing on top of the cells.....More of an issue in hot moist environments where there is more moisture available than in a house in winter in NE?
Your profile does not say where you are which influences the answers you get and how right they are.
but for the most pat, the Reflectix or Astrofoil type you describe won't do you any good on a practical basis. it must have an inch or so of air space in front of it to be effective in coming close to the claimed Rvalue equivalency.
Rafters you say? Is theis a cathedral cieling? That is also a factor on thesse answers. i.e. if you are in the south with such a situation, you might possibly be better off to put the reflextic an inch away from the roof sheathing and then use R15 FG unfaced
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Further to hurried post #5:
As you can see, when the reflective foil is contractor installed, the payback is about 29 years.. With DIY, it's about 13 years.
This attic only has about R15-16 fiberglass insulation. If there are no mechanicals/ducting in the attic, it would be better to blow about R25 cellulose for $700-$900 to get a good layer to stop heat transfer, no matter what type. Foam spray may cost $2,000-$3,000 and up for about 1500+ sq ft. and may be the way to go but savings will still be down the road.
Side Note: A lot of people claim that roofs/attics need venting to save the roof from the extra heat of an unvented attic. The roof shingles on a radiant barrier roof will get hotter as the heat normally coming to the attic is reflected back at the sheathing. With foam, very little heat will come through the shingle and sheathing so the temperature will be hotter than an unvented roof!!! What will happen to our roof material warranties??
What I'm getting at is the street level message "that you gotta have lots of venting so the roof shingles will last longer. Actually the difference in roof life between vented and unvented roofs is so little so as to be negligible. Bill Rose (Building Research Council at U of Illinois) has found top sections of vented cathedral ceiling cavities hotter than unvented attics and roofs!!
They also increased the attic venting as part of the full energy retrofit of this home to see which measures gave best bang for the buck. From the report:
Increased Attic Ventilation
Even with the installed radiant barrier system, the heat gain of the attic remained excessive. The home has small non-continuous screen soffit vents under the eaves of the roof (see Figure 36), but no ridge vents. The roof has black asphalt shingles, which get very hot; we measured surface temperatures in excess of 180oF. During baseline monitored, we recorded attic air temperatures of 143oF on the hottest days in July 1995. The ceiling has 6 inches blown fiberglass insulation irregularly distributed over the 1,768 ft2 attic floor. The actual R-value is not probably greater than R-15 as installed. Also, missing knee wall insulation in the cathedral ceilings results in further compromise to thermal performance (see Figure 2 and Figure 3).
With the attic radiant barrier installed in July of 1995, the peak attic air temperature dropped by almost 20oF and produced measurable savings in air conditioning consumption. However, we were still displeased with the magnitude of the attic temperatures (peaks 120oF on clear summer days). To try to further reduce this load, on August 12, 1996 we had a "Cobra Ridge Vent" ridge vent added to the attic.
Approximately 60 lineal of the roof ridge was cut to provide the added vent area. A two inch wide strip was cut from the ridge apex and the mesh ridge vent was then placed over the gap. The mesh was then topped off by shingles. According to the manufacturer, the effective free vent area is 16.9 square inches per lineal foot. On this basis, the added vent area is 7.0 square feet. Observing the installation (Figures 37 and 38), we had questions regarding its potential effectiveness. However, when the installation was complete, we could detect hot air exiting the ridge vent. In order to gauge the actual effectiveness, we performed a simple calculation based on the metered data. We compared the difference between the attic air temperature and measured ambient air temperature for one month before and after the retrofit. The result over a 24 hour profile is shown in Figure 39. The plot clearly shows that the added ridge vent reduced the attic air temperature. The average temperature difference between the attic and ambient over the daily cycle fell by 1.51oF, although the peak afternoon air temperature was lowered by 4.4oF. Assuming, 1500 square feet of conditioned attic floor area at R-19 and 375 square feet of R-4 duct, the change in the peak conductance is approximately 800 Btu/hr. With the given efficiency of the air conditioner (~13 Btu/W at peak conditions), this represents approximately a potential 60 W (2%) reduction in peak AC power. Annual energy savings from the retrofit were estimated at approximately 1% (45 kWh) based on a regression analysis of before and after cooling energy use.
The payback for the roof venting was 114 years!!!!!
So the 2 things that everyone seems to recommend had the longest paybacks. The new fridge, new pool pump and high efficiency lighting all paid back from 3.1 to 5.4 years.
Here's the website: http://www.fsec.ucf.edu/Bldg/pubs/cr978/index.htm#Economics
Thanks for all the comments. Sounds like the reflective insulation is no magic bullet. I probably will go with 1/2" or 1" Styrofoam on top of the batt insulation on the ceiling amd pick up a couple of "Rs".
For those who asked, the house is located in the northeast. This kitchen is an addition to a 275 year old colonial salt bot. The ceiling runs from 6'4 on a northeast facing wall to a maximum height of 9'4. This "new" addition was built about 60 years ago but was completely gutted due to insect damage.
Again, thanks to all.
"Further to hurried post #5:"
ROTFLMAO
That post took over an hour for you to edit five or six times!I was kind of shocked to find after I made my note above, that yours got three times as long as the first time I readit.no arguement, just found it funny that you considered it hurried off!;)
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Does the reflective insulation function as well as tinfoil hats to keep aliens from reading your mind? It's a pain to wear tinfoil all the time, especially in the shower.
You may be on to something there, Mark!
Let's experiment tonight. You put your AL hat on and take a look at something like a playboy magazine.
I will read your mind from here if I can. If I am right, we will know the foil doesn't work.Lemmee know when you have your reading cap on...
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I always have my tinfoil hat on.
I was trying to hurry off but the phone kept ringing on two lines and as I sat talking to clients, I'd see something or want to expand a bit! I was laughing at myself by the third!!