Radiant Barrier Foil Insulation - Why Is Air Gap or Space Required?

[KINGJOHN808]

Awesome video! Thanks again for the easy to follow explaination.

[ak99372]

Great video (I especially appreciate all marketing BS being excluded). I have a question. I was thinking of using the double sided bubble wrap around duct work. Do you have any recommendations on that? (I checked your website but I guess you focus only on attics)

[AtticFoil]

@ak99372 Bubble foil has an R-Value of about 1 since it's only about 1/4" thick. Any additional r-value you see advertised is in the form of a "dead air space" which is very tricky to achieve on ducts. It's not worth even trying. I'd keep it simple and buy some "duct wrap" - R-4 to R-8 with foil on the outside.  It's a standard issue product in the HVAC industry. Before insulating you want to SEAL the ducts with a good quality mastic. Seal then insulate. Need more info? - AtticFoil-dot-com

[AtticFoil]

@ak99372 Bubble foil around ductwork is a lot of work for very small benefit. You must be very careful to maintain an airtight airspace. You are better off using a standard radiant barrier/fiberglass insulation duct wrap. you will get more, r-value, it's cheaper and it's much easier to install.

[thermaldog]

is there a minimum air gap size for it to work...10mm, 20mm..?

[AtticFoil]

@thermaldog Generally, you want at least 1/2" if the air space is "sealed" or "dead". You can go down to a 1/4" if you have a ventilated air space. With a sealed airspace less than 1/2" you tend to loose some of the radiant barrier benefit due to conduction across the air space. If possible go 3/4" to 1" is ideal.

[bumhokim]

I heard there is new fire code for radiant barriers.......if you install radiant barrier that does not meet the new fire code, is it a violation of state or county code?

[AtticFoil]

@bumhokim There is a new testing procedure for flame and smoke. This is called the ASTM E 84 and ASTM E 2599. Nothing changes with the product except it must undergo a different method of testing. Eventually codes like the IRC, IBC, and IECC usually adopt the ASTM Tests. It will be a while before anything happens. Right now nothing has changed.

[ChrisUTMBA]

How does your product compare to the bubble wrap type stuff with foil on either side? it would seem like this would give you some built-in airgap.

[AtticFoil]

@ChrisUTMBA Bubble foil is a decent product. However, it usually works no better than AtticFoil - It's the foil doing all the work to reflect radiant heat. The only airspace is on the outside of the foil since it cannot have an airspace on the side that it is glued to something.

[1luckytexan]

Howdy Ed, I am SATISFIED CUSTOMER!

I DO have an interesting question about this video. What does this say about the effectiveness of the spray-on barrier? It is in direct contact with the bottom of the decking. This means it will conduct the heat into the attic right?

[AtticFoil]

Thanks!! I love satisfied customers!!

The paint is in direct contact with the bottom of the roof deck. By doing this, the paint or foil backed roof decking is working off the emissivity quality of the aluminum. The required air space is actually the attic space. The foil backed decking works very well and is good option for a new roof deck.

The low emissivity surface from paint or foil causes most of the radiant heat to be lost upward from the roof rather than into the attic space.

[psbmastering]

I'm considering to install this AtticFoil in my attic but am not sure if I need to install it on the attic walls (rafters) AND the attic floor (already covered with blown-in insulation). Would the AtticFoil installed on top of existing blown-in insulation be enough to work its magic, or should I apply the atticfoil on the rafters as well (in addition to the floor) in order to get the most benefit out of this product?

[AtticFoil]

Usually one layer is all you need. Putting AtticFoil on both the bottom of the roof rafters AND on top of the insulation will have a some additional benefit.

When you consider the extra time, money and effort for the second layer it is usually hard to justify doing both. I have had some customers do both with great results. I would only consider doing both in a mixed hot & cold climate area. Visit AtticFoil(dot)com and look at the "Best Install Method" page for more info.

[b2525]

Great explanation. I live in New England and am considering putting this up in my attic as well as in a couple of crawl spaces in my basement attached to the rafters. I basically want to trap heat in the attic and above the basement. My attic is about as high as the one in this demo. How much heat do you think I could realistically reflect back if the areas are cold to begin with. Attic is a little warmer than outside temp.  Thanks

[AtticFoil]

Trapping heat and trapping air are two different things.  You cant use the attic temp as a gauge. Ideally, you want you attic cold and dry. Radiant heat will still be reflected back by the foil. Your "Thermal Envelope" should be an airtight box, that is well insulated to reduce air infiltration and conductive heat loss. Then, wrap that "box" with foil to reduce radiant heat loss/gain.

[LexisCoatings]

Do you use galvanized staples with aluminum?

[AtticFoil]

Yes, generally galvanized staples are used. There could be some reaction between the steel and aluminum, but the contact area is so small this is not a big concern. I've got thousands of customers and never heard that it was an issue. You could use plastic staples if this is a big deal.

[Stitch35]

cool ty

[grayboy03]

Excellent info on explaining how radiant barrier works.