Do Radiant Barriers Actually Work? Head to Head Comparison Test!
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- Опубліковано 22 лип 2021
- There is a lot of debate online as to whether radiant barriers actually work, and if so - how. In this video, Jordan builds two identical doghouses using LP TechShield Radiant Barrier roof decking. The only difference in the two is that one dog house is built CORRECTLY - with the shiny side in towards the attic , and the other is built INCORRECTLY - with the shiny side facing out towards the sky. The results are impressive with the LP TechShield installed correctly beating the incorrect install by 18-20 degrees F. This translates directly into less heat load on cooling equipment and a lower energy bill, especially in hot climates.
So how does a radiant barrier work?
Heat transfers in three ways: radiation, conduction, and convection. The sun's rays radiate to the earth through space via, you guessed it, radiation, and require no medium like air, water, metal ect. to transfer. Some of the suns energy is radiated directly onto our homes roof where it is absorbed and transferred via conduction. Conduction is the transfer of heat through material. Think of a frying pan on a stove. The hot flame transfers heat into the frying pan, and the frying pan conducts through itself and into the food that is in direct contact. A cast iron frying pan's handle will get hot even though it has not come in direct contact with the flame. The heat has conducted through the pan and into the handle. The same thing happens on your roof. The suns radiant energy is absorbed into the roof and the heat is conducted through the roof materials to the bottom side of your roof deck. When the roof deck is hot, the energy will try to find equilibrium with the surroundings. Some of the energy will conduct into the surrounding rafters. Some of the heat will conduct into the adjacent air, which will in turn become buoyant and move, resulting in convection (the movement of heat through the movement of a medium) and some of the heat will re-radiate into the attic space heating the insulation below, which will in turn conduct heat towards your conditioned space.
Now, there are very effective strategies to combat the movement of heat from the roof to the conditioned living space. A well ventilated attic with allow heated air to escape through the ridge vent and allow cool air to enter through soffit vents limiting convection, and good insulation will limit conduction into the living space. But what about the third mode of heat transfer - radiation? This is where a radiant barrier comes into play. The aluminum backing on LP TechShield is a low emissivity material. This means that it is not a very good radiator of energy. So the energy that has been absorbed by the roof and conducted through the decking is not easily radiated off the underside of the roof decking and must find another way out - either by conduction, convection, or re-radiating back into the sky.
The real-world results for installing LP TechShield radiant barrier is about a 20 degree Fahrenheit cooler attic temperature, which is significant.
However, to achieve this advantage, it is critical that the product be installed correctly! This means that the low emissivity backing (the shiny side) is installed inward toward the attic. It seems intuitive to place to shiny side our to "reflect" the sun's rays, and this might have some effect if it weren't for the pesky need to put some sort of roofing in direct contact with the decking rendering the reflectivity pointless and changing the heat transfer mode to conduction.
Now that we understand how radiant barriers work, and have seen in real world testing that there is a significant difference in attic temperatures, the remaining question is that of cost. Is there an ROI for installing radiant barrier? In a renovation situation, I am not sure if a add-on product, whether foil or paint, is worth the time and expense. However, in a new build or complete re-roof of a ventilated attic where you must put down a roof deck anyway, I think it would be a missed opportunity to improving the comfort and performance of your home by using LP Techshield.
JUST MAKE SURE YOU INSTALL IT CORRECTLY!! SHINY SIDE IN!!!
Even the 'correct' one is incorrectly installed without an air gap.
this is great. now build one without any radiant barrier whatsoever and one with an air gapped radiant barrier
I wish more builders would get on that soap-box with you. That was the best explanation of radiation, convection and conduction I have ever heard! thanks.
Your analysis of convection and conduction is correct, radiant is not. Heat does not travel by radiation, heat is the conversion of radiation into thermal energy.
Flip your foil around and add an air gap between the shingles and radaint barrier, it will work much better. Just like they do with satellites in space... foil needs to face radiation source.
thank you so much for clearly explaining how the 3 methods affect us and how Radiant barriers work. It's so great to see you putting out content again!!!
The property that aluminum has going for it is its emissivity coefficient, a measure of how much infrared it radiates compared to a perfect "black body" which has a coefficient of 1. Aluminum foil typically has a coefficient of 0.04. Wood is typically 0.9 or higher, so aluminum foil will radiate about 20 times less infrared than wood if they're both at the same temperature.
Great explanation!
Easy way to remember it, is it needs an air gap to be able to work. Foil faces the air gap. I think min of 1 or 2" required.
He returns!
Good to see your videos again!
Thanks for this video. What I did was do both. I just had my roof done and silver side up. I also had radiant barrier SPAYED done in my attic (giving me a 50-60 degree difference) and had 7-10 inches of insulation added, attic tent and I have two a/c units for each side of my 2500 sq. ft house. Sealed all my can lights, changed all light bulbs to LED's. My utilities went from $400 to $100. My thermostats are on 78 and 82. I also used purple insulation on the garage door. Whoo Hoo.
Great Explanation. I've been using radiant barrier and foam in all my new builds families are HAPPY this helps reduce Electric Bill here inTEXAS!
Thanks for that awesome explanation and sample.
It's a great comparison, I would have liked to see the temperature difference inside the cabins as well. And I'd like to see if there would be a difference if you added venting in soffits and has a tower vent. Great stuff.
Informative, but I think that you need to check your math. 8:50 You're looking at 50 & 70 degrees over the inside target of 70, not 40 & 60.
Great video. Thanks very much for the info.
You should have made 3 dog houses. The third one should be made without a radiant barrier.
Does anyone build a roof like that? Do you even need a radiant barrier if you are willing to build what equates to the cost and materials of two roofs?
Make a third doghouse and put the aluminum facing up. Tape the joints and nails. Put 2x4 furring on that. Deck it again then roof it. Check the difference between it and the others.
Good job teaching!
Excellent video. Thanks
Thanks Jordan....I wish there was a control dog house for this experiment
what happens if you add an air gap between the shingle and the aluminum (faced up)? does the air gap change anything because now the shingle is not conducting heat?
I put this on a shed and a modern pergola I built you can feel the difference for sure. Good product.
Thanks for definitively clearing that up!
I wonder what the temp. would have been if there was NO radiant barrier at all. Same as the incorrectly 'installed' dog house?
The proper experiment would have a control dog house built with no radiant barrier. Then take the results for all three and compare. I believe in the concept of the radiant barrier but become skeptical when obvious third dog house has been omitted.
@@robertkarl29 may as well go one further and add a fourth with an air gap. that would make it one of (if not) the most definitive comparison videos on radiant barriers ever
Great lab assessment, could you now build the dog house with spray foam and with a dual frame ? could you also get a third temperature of the local weather measurement
Thanks for the video Jordan.
Could you do this with other roof designs, e.g. insulation between the trusses that would be touching the aluminum, or a flat roof with insulation above the OSB, or how about siding with a rain vent behind it so there's less conduction but want to prevent radiation from the siding/roof to the OSB. What if you're in a colder climate and have to keep heat in. Would you install the radiant barrier in the same way in all of these cases?
The last time you had a video about this, someone I follow on IG was putting a similar product to this right over existing roof sheathing. After letting him know that without an air gap it wouldn't do anything, he talked to his roofers who must have researched it a bit more, and they agreed. They then charged him the same price as a premium osb roof decking of the same thickness.
Btw, did that shed get an addition?
Very interesting video. Does the same apply if you have a steel roof instead of asphalt?
In the vanlife community (those that live full or part time in vehicles such as a Sprinter van), there is a lot of misinformation on how best to install the radiant barrier.
We've done this - steel roof, air gap of 2cm, then reflectix radiant barrier, then 2cm air gap followed by insulation followed by wood panels for our ceiling.
Is this the way to do it?
Hey Jordan, what if im building a warm roof and I have the shiny side facing the air gap which is "out." Is it worth it? Thanks so much man. Love your videos
Does this product do anything for keeping heat inside the home during the winter?
Thanks
Please do a test to show the difference under the attic insulation. Thanks
That will only show the ambiant air temp though as there is no insulation on the walls and no door
I'm guessing that this is more popular in area without cold winters. I don't see it at all around Ontario, Canada. Just well vented attics to protect asphalt shingles from getting hot enough to cause degradation in the summer and ice damning near the eaves in the winters. Then a big layer of insulation between the attic and the living area.
Great example of how it works.
In Australia foil barrier is sometimes 'draped' under the roof in thin flexible 'film' sheets.
This is usually a retro fit.
I wonder how much better that would be with 2 air gaps?
The surface facing up could become dusty over time.
Does that dust effect the emissivity on the upper surface?
I think it actually pulls double duty when hung like that. The air gap on top lets it reflect heat (basically its reflectivity is as high as its emissivity is low). Even if the top gets dusty and it absorbs more heat, as long as the bottom is shiny, it still won't emit much downward.
This is just kind of speculation based on physics fundamentals - I basically never hear anyone talking about both features at once. Makes sense to me, though.
My builder installed the OSB with the foil side toward the attic. Plus, he installed Galv-alum standing seam steel roofing. I'm not sure that's better or worse than what the folks selling the foil radiant barrier and telling us to install it on the bottom of the rafters or trusses to leave the air gap between the roof deck snd the radiant barrier. Your opinion?
Thanks .. allways wounderd . Would aluminum radiate if it was laying on HD styrofoam?
In my attic I have to install shiny side pointing into the attic. Reason? The HUGE amount of heat in the attic that I need to reflect away from the living space.
So far it has kept the livable space a decent and constant temperature with no wild swings in heat.
What about that foam insulation that is shiny on both sides?
Thx bro for this experiment
Love from India
5:06 Would it be correct to say that it's an emissivity heat transfer question?
any more update in 2024? how about just painting the roof? how much difference will it made?
What about radiant barrier/techshield for walls?
How about a 3rd dog house with NO Radiant Barrier to prove it doesn't work at all.
Roof vent + air gap + radiant barrier = Win. I don't think I would use LP TehShield RB. Maybe they can make a product with an integrated air gap so the warm air can move out with natural convection.
I love the dog house experiment
I'm going to be building my house with ICF walls in southern AZ. For the roof I want to do closed cell spray foam in addition to radiant barrier on a metal roof. What is the best way to install it? Is that considered overkill?
Roof deck
Felt or synthetic barrier
Radiant barrier
Purlins
Metal roof attached to Purloins to provide the required air space
I’m guessing same properties/principles would apply to putting a radiator barrier on a metal garage door?.
I could swear that Scott True mentioned you as his duct designer. But someone else designed yours?
How about a video on a spray on radiant barrier?
I don’t think there are more than 3 videos. I might get a bucket of that paint and spray it on my unfinished garage rafters/sheathing to see if it actually keeps heat in, (In Utah, gets below freezing at night) and in the day mid summer, gets over 125 in the garage, place is a sauna).. looking to just keep heat in at this point, now if I can just find me some of that paint, and if I can spray it with airless sprayer..
Should have built a third one with no lp at all to see the difference in attic temp
Usimg electric air ventilation as heat exhauster on you roof will do the same for quite cheap like factories have on their roof... to release hot air trapped...
I find this counterintuitive, but I don't doubt it is true. I think LP TechShield is mostly for warmer climates. Don't forget to vacuum the aluminum side from time to time as dust reduces the effectiveness. I wonder if money would be better spent getting more reflective roofing. It's odd that my cars "radiator" is made out of aluminum. I guess "convector" was taken.
radiator, radiates heat.
@@FullSendPrecision My understanding of the video is that the aluminum attached to the OSB stops or reduces radiation. Seems weird. I think car radiators work primarily through convection.
@@59seank we’re both right. Think back to how old houses are heated. Radiators :)
@@FullSendPrecision I have fond memories of cast iron radiators. I had a favorite chair near one and it kept me toasty warm as opposed to the leaky single pane windows and barely insulated walls.. It didn't dry out the air like forced air systems.
@@FullSendPrecision Radiators increase surface area to allow heat to pass form one fluid to another faster.
Silver side is supposed to go up, but you have to leave an air gap. I suspect that you got a lower temp on it installed silver side down because you put a less conductive material against the hot roof, but had you left an air gap, you would have gotten an even lower temp with the silver side up blocking the radiant heat gain. It needs the air gap to prevent heating by conduction (like an aluminum frying pan on a hot plate).
although that is the optimal installation method for a radiant barrier, i don't believe that is the intended use of this particular product. it seems to be a middle ground, in the event an attic space is finished out for occupation
Installed backwards… wouldn’t that just super heat the shingles and cause them to deteriorate faster?
I don’t know, but I doubt it. The radiant properties of the material go away as soon as it contacts the shingles. My best guess is that the aluminum will turn into a high-efficiency conductor, pulling the heat away from the shingles into the OSB below. So best guess- it will just be inert?
My bubble foil comes in both sides shiny. What now?
Staple it to the rafters and let it pull double duty. Top side reflects most heat, bottom side will behave exactly like the down-facing foil here. In theory this should work even better than in the video, because if it's integrated with the board, you don't take advantage of its reflective properties.
Thought there was supposed to be a gap
Cell phones don't seem to work after install. Bummer
I’ve missed you.
Repeat the test in the North in the winter...
Since no one is saying this you should have made 4 dog houses.
Good information, but this video is longer than it needed to be.
Dude, where you been? I thought you were dead.
my guess is there is a housing boom going on and he is charging a premium while times are good.
hey Jordan, you are actually pretty good at explaining theories. The first few minutes could be done better, if cut to a white board and explain the theories with drawings instead of standing next to the 2 props. Just like how Steve B does it with his big red. and then you can cut back to the 2 props to prove your theories. Great to see new videos from you. cheers
3:52 The what?
Howdy
5:14 .lmao ..the what now?
What
Sounds like a bunch of hooplah
There's two kinds of smart: The smart that can DO, and the smart that can TEACH.👍
I don't have a dog.
LOL 😂 Go back to school Jordan You’re not even close to how a radiant barrier works.
This is a commercial, this is not an informative video ….
This is wrong.