Sherwin Williams has a paint product that is sprayed or rolled on the underside of the roof deck that acts as a radiant barrier
rockinroger
| Posted in General Questions on
Does this product work? Or should I use the “bubble wrap” stuff?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Roger,
No one has yet invented a radiant barrier paint. The product doesn't exist.
A radiant barrier must have a emissivity of 0.1 or less. No paint qualifies.
Even though there is no such thing as radiant barrier paint, there is a category of paints called “interior radiation control coating system” (IRCCS). The threshold for an IRCCS is less stringent than for a radiant barrier; to qualify, the emissivity of the dried paint film must be 0.25 or less.
The Sherwin Williams product (E-Barrier Reflective Coating) doesn't even meet this less demanding threshold, since it has an emissivity of 0.36. (Source: Environmental Building News.)
That doesn't stop Sherwin Williams from lying about the product on their website. This page falsely states: "The Fast Facts On E-Barrier. E-Barrier is: An energy saving coating; A radiant barrier."
Does it work? Sort of. It is a low-e coating, but it doesn't work as well as a radiant barrier -- and even a radiant barrier is worthless in a well insulated house. More information here: Radiant Barriers: A Solution in Search of a Problem
And concerning your question about bubble wrap: you're just teasing me -- right?
Thank you for your answer. I thought as much. Actually, if the product did exist, I thought that i would inject each little bubble with the paint. lol.
There's definitely a separation between the "does it work?" part and the "should I use it?" part. Rare is the answer to the "should I ..." section an unqualified "yes", but there are the rare exceptions.
From a cost/benefit point of view the low-E paint is so cheap that it has a higher rationale than the somewhat more effective aluminized bubble-wrap type radiant barrer (RB). No reflective "insulation" has a huge benefit in a single layer, but multiple layers separated by air spaces can. From a cost/benefit of the type of construction detials required for adequate multi-layer RB solutions buying insulation that has an ASTM C518 labled R-value is usually the better deal.
On a recent thread here I (somewhat reluctantly) recommended low-E paint on the roof deck in conjunction with high solar-reflectance "cool roof" shingles and rafter mounted foil or aluminized fabric (not bubble pack) RB as a means of reducing the heat radiating from a high roof in an unheated non-air conditioned island building. The net effect on the PEAK heat transfer between the roof deck and the floor level where the humans congregate would likely exceed that of putting R10 above the roof deck.
But file that recommendation under "rare exceptions." For actively heated/cooled buildings with year-round occupancy putting the money into more insulation would provide a much greater benefit.