Radiant Barrier Department Of Energy Lab Test Results - (Understanding Reflectivity vs Emissivity)
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- เผยแพร่เมื่อ 4 ก.ย. 2014
- atticfoil.com/index.php/techn...
Depending on which side of the double-sided product the air gap is one, AtticFoil will either use reflectivity to reflect heat, or emissivity to block it. Radiant barrier decking (ex. TechShield or Solar Board) uses emissivity, where as stapling AtticFoil to the bottom of the rafters uses reflectivity and is more effective at reducing heat transfer.
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When the foil pressed up against the hot surface, heat transfer happens 100% by conduction. When there is an air gap between them, the heat transfer happens by radiation and convection (and conduction from the foil to indoor air). Since the foil is so good at reflecting thermal radiation, the latter works better. Even though I knew the physics behind it, it never occurred to me until I watched this video. So thanks a lot!
Thanks for the comment!
Your vid told me EXACTLY what I needed to know before I put this stuff up. 20% better is a big difference so I'm going with reflectivity by attaching the foil to the inside of the wall sheeting I'm installing.
I can't believe people are watching this and THEN asking the questions you just answered.
Thanks for the kind words!
Thank you, just thank you.. took me a long while to get my head around it
Reflectivity, emissivity, glad it makes sense now.
Got my first house and i want to make it as comfortable as possible. Im going to buy this. Nice
How did installing www.AtticFoil.com turn out?
That pretty much answered my questions.
We try!
As you can see from the video, many people get tripped up about which side of the foil the air space is on and it can be confusing. If you have questions about an install or where to place the foil, ASK US!! We are the experts and we can help you out. You can leave your comment below or give us a call!
I was planning on putting batt insulation in the cavities and the attic foil draped over the rafters. Would this work?
@@1225eal Can you list all layers including airspaces from the outside to inside? Example? Shingles/roof deck/airspace/foil/Insulation/drywall. Sorry, but I need more details on the whole assembly.
This one is different . If you glued radiant Berrier down to the outside roof of a rv/ house trailer would the reflective properties of the foil help keep heat down inside of the rv.. glue it straight the the roof
It may help some, but the primary benefit would be to reflect heat and keep it out.
Hi Ed... Thank you, thank you, thank you! I've been seeking this answer and it's been driving me nuts. I'm a educated guy, and even a bit of a science dork, so I completely understand and conceptually GET the difference between the three main forms of heat transfer: Radiation, Conduction, and Convection. What I did NOT get is how it was possible for those products like LP TechShield to have ANY effect at all. If I'm standing 1ft away from a large campfire and hold a sheet of foil in front of me I'll be cold, cuz I'm blocking virtually all of the radiant heat of the fire, but if I wrap myself in that foil tightly in that foil I'll cook, because at that point the foil itself will heat up and through contact it will heat me up. So how can Techshield have an effect. I finally understand that it HAS AN EFFECT, just not nearly as powerful of one.
I live in Atlanta, GA and we are about to build a home (I myself am a roofing contractor). I know there has been case studies done on Techshield type products and they do seem to (w/ minimal effort) have a decent and measurable effect. I have not costed out the product to see how much more than regular OSB it costs, but I imagine it's not a HUGE difference. I'm betting a guy like you has read the studies and has done the math... Since attic foil has even a bigger effect I absolutely plan on using that (even though it does take more effort too). If I'm building from scratch and can afford the increase in material cost for the decking, do you think I should use both Techshield AND use attic foil?? Or should I skip the techshield type stuff and ONLY use the attic foils systems?
What are your thoughts about batt insulation vs. blown insulation (I watched your video about fluffing and would be sure to purchase by units, not inches)? I worry that blown insulation, even with baffles, may clog up my intake vents, it gives a more uniform coverage too.
Techshield is usually a pretty cheap upgrade. Maybe $2 per sheet?? So, it's worth it. We have had many people use both with spectacular results. Or, and in-between method would be to drape over the rafters and let droop down between. www.roofingfoil.com/install-photos/under-new-decking/ As for keeping insulation out of the soffits? Run the foil up a foot or two then leave a gap before the next piece. You just want a path for air to get both between the foil and the roof and into the attic under the AtticFoil. For insulation? Blown insulation is usually best since you can easily fill and cover all the small hard to reach areas. I've also seen batts put in up the the tops of the ceiling joists and then blown in on top. This works good too.
@pedram Pete you're only understanding part of the concept. Wrapping yourself in tinfoil and cooking is only part of the concept. When the foil is directly touching the wood.... the foil itself gets hot, the roof gets hot, the siding gets hot. It however does not radiate that heat. So the items inside that are not directly touching the foil....don't have heat radiating into them
I wouldn't worry too much about blown insulation clogging the soffit vents, you could always get the attic blown before the soffit is installed, that way you'd know the vents are clear of any insulation.
Myself I prefer cellulose over blown fiberglass, batt insulation does not perform well in an attic.
Hello, Is it ok to add R-13 piece insulation between the outside wall and the foil when the foil is placed in the emissivity heat (attic foil is nailed on the rafters/studs on the inside of the house)?
David, can you clarify EXACTLY all the layers from the outside to the inside? Including any air spaces? As long as the foil faces an airspace it will work off of either reflectivity or emissivity.
Great content. Quick question for you. My newly built home has the aluminum built into the roof decking already. Our second floor AC unit constantly runs during the summer time. Would it be beneficial to add your product to the boards to create that air gap? Would the benefit be cumulative? Thanks!
Here is a real simple way to determine if a radiant barrier will be beneficial. If you put your hand a couple inches away from the roof decking and you FEEL radiant heat, then stapling to the bottom of the rafters will be beneficial. The radiant barrier decking works OK, but combined with stapling www.AtticFoil.com on the bottom of the rafters, the results are AMAZING. We have a bunch of high performance home builders with do BOTH! It's hard to tell if the sun is out or not while in these attics.
@@AtticFoil I though same thing. Have a house in Central FL. and needs new roof was going to put reflective barrier on roof looking at metal roofing. Now think will do both.
Hello! My husband and I will be installing this in our attic, and we're wondering if stapling 2 layers instead of just 1 would increase the benefit further. Has AtticFoil tested this at all? Thank you so much for your videos by the way. They've been incredibly helpful and informative!
+FloJoMoJo You will not get much of a benefit from installing an additional layer. It's kinda like wearing two raincoats. If the first layer is reflecting 97% of the radiant heat, there isn't much getting through for the 2nd layer to work on.
+AtticFoil Radiant Barrier Foil Insulation Thank you for your response! This helps immensely.
have you tryed putting the foil on top of the insulation in an attic and putting it under the rafters?
Yes, we have had many customers do both with great results. Once you staple it up, laying over the insulation is easy. This method will create a better year-round benefit for homes that have ductwork in the attic. You want to BOTH reduce Summer heat gain, AND reduce Winter heat loss.
Are there any issues with using both emissivity and reflectivity? Our roofing already has a silver lining under the wood and above our rafters. I'm considering adding another reflective barrier under the rafters. Our ducts are in the attic and we are in a warm Texas climate. Thanks.
No issue. In fact, it works GREAT! The radiant barrier decking is OK but combined with www.AtticFoil.com the results are amazing. We have several builders who do both with great results!
Does it matter if the insulation is on top or below the barrier? I have ducts in my attic and so i want to bring them inside the air conditioned space. So I was going to install insulation in the bays between rafters. In what order should the 3 pieces go? Should it be vent channel baffle, fiber glass, then foil? Or should it be Foil, vent channel baffle, insulation? Or can I omit the vent baffle channel and use the foil to make one then put the insulation under the foil? Which method will give me the best result?
I'd go roofdeck > air channel > Foil > Insulation (sealed airtight) > some type of interior air barrier > attic space. You will get both a radiant barrier and a conditioned attic for your ducts.
What do you recommend? Real foil, thick industrial grade, as the material itself has a role or the foil coated mylar material?
Real aluminum like on our www.AtticFoil.com products. Our foil is actually REALLY thin. The thinner the better for reflectivity. This is why we laminate it to a woven PE fabric (like a blue tarp) to make it tearproof. NEVER use MPET or mylar. It will oxidize. atticfoil.com/index.php/technical-info/metalized-radiant-barrier-film-oxidation/
I have a 40ft. shipping container in the northern South Carolina-area, approx. 10 miles from the beach. My plan(for the exterior) was to paint the outside with automotive reflective paint. Then (for the interior) was to put the reflective material directly to the wall AND then put R19 insulation between the studs. Is any of this wrong? ...should I consider a different approach?
OK, so looking at emissivity tables youcan see that foil emissivity is 0.03 and wood is 0.9. So foil is going to radiate a tiny fraction of the heat that the bare underside of OSB sheathing would, but there is still going to be direct transfer of heat by conduction to free moving attic air that will convect. Is radiated heat really THAT much of a component in this situation?
Not sure if you have ever been in an attic in Texas in July but YES Radiant Heat Is HUGE! Air gets hot from the cooling effect of pulling heat off the deck as it moves by. It's basically an air-cooled assembly. But radiant heat goes right through air. Otherwise, we could not have a cold/sunny day.
@@AtticFoil Yes, I understand how radiant heat transfer works. As I said, I would have thought that conduction/convection across the underside of the sheathing would've transferred more heat than radiation because I didn't realise that wood radiated so well.
with attic foil on the rafters, how does heat fare with it coming up the rafter channels (that air space) and only has room to go out of whirlybirds? I know a ridgevent is already designed to where it'll go straight out the exhaust but with whirlybirds it seems like alot of heat will recirculate back through the attic and move out sooner or later but not as efficient as a ridgevent or on a roof with hips. Please let me know what you think
Don't overthink it. Hot air all ends up in the "top" of the attic. Like water in a tub heading towards the drain. In fact, hot air does not actually "rise" it is LIFTED by cooler denser air. This is air coming in the bottom of the attic. So, not a lot of "recirculation" you mentioned. The hot air will find a way out whether ridge vents, wind turbines, passive vents, gable vents etc.
If I have radiant barrier OSB with foil facing out (on an exterior wall of a shop) and put siding (Hardie plank) directly on top, with no air gap will it still block heat? The air gap as I see it will be on the inside of the shop because of no drywall etc.
It depends, If it overlaps and there is a small triangular airspace behind it, you will still get SOME benefit. If it's more like a shiplap profile with full contact to the foil, you won't get any benefit.
Ok, so if techshield on the bottom of OSB blocks 30%, and the reflective foil blocks 50%, then why aren't we seeing foil backed drywall or gypsum board to reflect on vaulted ceilings or sunny walls? Seems like there's a market for that where you can't install the foil to a vaulted ceiling. thoughts?
Here is how you do cathedral ceilings: th-cam.com/video/CjwZXoRzRiM/w-d-xo.html You would typically not want a radiant barrier "inside" the insulation. Radiant barrier first for radiant heat, regular insulation next for conductive heat.
I have solar board on my new house. If I added a solar shield to the studs, keeping the eaves and ridge vents clear of course, would that help or hurt?
We have several home builders who do both on all the new homes they build. The solar board is pretty good considering the cost. But, combined with www.AtticFoil.com it's amazing you will feel virtually NO radiant heat coming off the roof. Usually you cannot tell if it's sunny or cloudy inside the attic.
Can you still put over even if you have the foil up against the wood like that well would it work or just waste of time
You can definitely staple it up below the radiant barrier decking. We have several home builders that do bot on new construction homes and they love the results. You can stand in the attic and can't tell if the sun is out or not! So, there is benefit. As for is it worth it?? It depends, If you can DIY it then I'd say yes. Paying a person a bunch to install it? The payback is gonna be a super long time.
Can I install attic foil at the bottom of the rafters even if my roof has the solar board decking? is it going to cause any problem? the attic has ventilation all the way around
You can do both and get some additional benefit. Not sure if it is worth it. It really depends on how much time, money effort is involved. www.atticfoil.com/index.php/technical-info/dept-of-energy-study-results/
If there is no incident infra-red radiation, then there will be no benefit to erecting another radiant barrier. But I doubt your "solar board decking" is so perfect; I except it gets dirty and increasingly dark with time, and therefore become a greater and greater source of IR beneath.
I installed a foil radiant barrier, stapling it to the underside of all rafters, in my residential garage to enormous effect. I expect efficacy to diminish somewhat each year as dust and dirt accumulate on the top side; but the bottom remains a near-zero emitter, and that's what's most important. I even wrapped existing lumber, beneath the foil sheet, in shiny aluminum, so that heat cannot radiate from those items (e.g., bike hanging hook members made from 8' x 2"x4", bolted to underside of rafters).
A nasty surprise was that the gap above my radiant barrier became a rat magnet. It took months to fix that problem, with patient use of bait and humane traps, etc. Yeah, I had a small entry hole in my roof and some long-forgotten grass seed, on a shelf, that attracted them. But they ran atop the radiant barrier foil with impunity.
John, thanks for the comments! Be glad you used a heavyweight No-Tear Radiant Barrier Foil like we sell at www.AtticFoil.com I've seen pictures of a whole attic of the cheap stuff end up on the floor of attic when a couple critters weight was too much for it to handle.
Emissivity vs reflectivity Which is better as far as keeping a room cooler or is both equal
Reflectivity is best if you can get the airspace on the hot side.
@@AtticFoilso if we can get the airspace on the hot side in assuming the reflective side should face the air space? Thanks a lot 🙏🙏😅
would there be any benefit to doing both radiant barrier decking plus foil barrier with an air space?
We have had many builders do both in the South with amazing results. The radiant barrier decking works pretty good. But, combined with the www.AtticFoil.com on the bottom of the rafters and you will virtually eliminate ALL radiant heat coming into the attic.
@@AtticFoil That's great!
Was the 50% both combined or just the atticfoil on rafters?
JUST the www.AtticFoil.com They did not do a "combined" method test.
I live in the mountains of VA. I have a shingled roof then osb board then insulation. can I staple foil to rafters then put sheetrock. Will this cause condensation? I will not have an air space as the attic is a bedroom.
Uh, tricky question. Products do NOT CAUSE condensation. Condensation occurs when warm-moist air comes in contact with a relatively cool surface (Below the dew point). Just like breathing on a mirror. So, without more info I really can't make a call. Feel free to call us. More info on condensation here: bluetexinsulation.com/pages/moisture-in-metal-buildings-causes
If I go reflective with airspace on hot side in a small 8 x8 shed with radiant Barrier is that enough to call it insulated being on a budget?
"Insulated" - probably not. "Much More Comfortable" - Yes!
So I'm redoing the roof on my rv. I'll have foam insulation with appx 1/2 to 3/4 inch air gap between the insulation and decking. Which would be better to have a radiant barrier on the decking or insulation?
I think it's better to work off the reflectivity quality rather than the emissivity quality. Can you go? Roof>Airspace (furring strips/battens etc??) >Radiant Barrier >Foam Insulation > Decking. This can be tricky with the limited details provided. Feel free to contact us at www.AtticFoil.com www.RoofingFoil.com for more help.
You guys in central jersey?
No, we only sell direct direct. www.AtticFoil.com, www.WareHouseFoil.com
So are you suggesting to use both one on the wall and one on the studs? Or just the one on the studs?
Working off of Reflectivity is best. However, from an install perspective, sometimes it's easier to install using the emissivity quality.
Is reflectivity the one against the wood sheets? Or the one that goes across the studs?
@@desertrider325 Reflectivity is when the airspace faces the HOT object. In this case stapling to the inside of the studs with the airspace between the foil and the hot sides/roof. Emissivity is when the airpace faces the "Cool" side like when you wrap a hot potato to KEEP it hot.
I live in a mobile home that has skirting I'm looking for an outside barrier to keep some of the cold out can you help me out
We had several customers use the www.BlueTexInsulation.com products for applications like this with good success.
What if you do both? Or were those 50% numbers including both?
We have had many people do both with amazing results. www.AtticFoil.com
Is this emf protection also?
Although we don't promote the product as RF/Faraday Cage/emf type product, we have had many customer buy a lot of product for this purpose. (whole buildings on interior walls, etc.) Because needs are specific, we recommend getting a sample or single roll and testing to see if it meets your requirements. Generally speaking, any pure aluminum product would reduce or eliminate RF signals.
Is that the same with cold? Like if it's cold outside and you leave that air gap will the cold be reflected back outside?
Technically, there is NO such thing as "Cold". It's just a lack of heat. To some degree it will reflect the heat BACK to the inside from escaping.
What happens if you have a water leak in your attic and the rafters are foiled up? Won't it be undetectable since it's invisible?
Not at all. Normally you install www.AtticFoil.com from the bottom upward and do not tape the seams. If you have a leak it will only run down less than 4' and drip off the edge of the AtticFoil. It will also leave staining on the edge. It's actually easier to find a leak with the foil installed.
does this block 3g, 4g, 5g, wifi etc?
We don't officially sell it for these purposes. However, we sell a LOT of product for this purpose. We always tell customers to get a free sample or a small roll to test to see if it meets there needs. Usually, they end up ordering. We had one customer put in 50,000 sq. ft in walls inside a building for this reason.
What about wintertime when you are using a heater if you don't put insulation in? Example: im converting a ahed into a home office
For this type of application take a look at our metal building insulation products that combine radiant barrier and foam insulation. Or call us! www.BlueTexInsulation.com
Where can I get the same stapler?
Search "Front squeeze T50 stapler". There are several brands/types.
Can I keep the airspace 2-3 feet after roof?
Yes, does not matter where or how big the airspace is. You just want to break the path of heat coming off the roof into the insulation when installing www.AttticFoil.com
What if you do both?
We have had many customers install www.AtticFoil.com doing both methods with great results. Typically, these are customers in mixed climates AND they have ductwork in the attic.
what if you do both ?
Great question!! We actually have several homebuilders that install both www.AtticFoil.com and the radiant barrier decking. Amazing results. You can stand in the attic and not know if the sun is out.
Can they work together?
Maybe? Depends what you do. Contact us at www.AtticFoil.com
My house is all foam, in Houston. 3 thousand square feet. I have a 3 ton unit. Keep attic at same temp as in the living space. 74° with 95 out door temp. I have a Trane variable speed unit. My monthly light bill. 80 dollars. Hum level indoor is 48 % , attic hum level 48 %. All ducts are R8. Provide a small amount of fresh air into house. I have a Honeywell dehumidifier that also provide fresh dry air from out door. Never seem my unit ( compressor ), work at more them 50percent capacity. At night time, unit reduce speed at 25 percent. Better then that foil thing.
Nice to know. What if anything does your comment have to do with the video??
@@AtticFoil I suspect he is a troll, but he inadvertently provided an opportunity for me to ask a question about a house such as his. Say you have an attic fully insulated with spray foam, would there be any additional benefit to adding radiant barrier foil underneath that, say if there was a slight air gap? In other words, is there enough radiant heat coming through that spray foam insulation that could be reflected out enough that it would be worth doing?
@@NateInTX Would it help? Yes, some. Is it worth it? Probably not. Normally to keep heat out we want the foil to be our first line of defense against radiant heat and the insulation to be the second line of defense against conductive heat.
It probably is a good video... However it isn't worth listening to if you can't increase your volume. Can't here you!
I think it's an issue with your hardware. I asked a couple friends to check and they could hear it fine. Or, you can turn on the Closed Caption.