I concur with Scott and David, and when Martin has any measure of professionalism he ought to retract his short article. Or possibly as Scott implies, the editors of GreenHomeAdvisor should request Martin to retire as he clearly does not understand the issue very very well or has another agenda.
The one way it could sound right is IF you suppose which the "cellulose" household features a inadequate air control layer and Should the mechanical devices and ductwork are inside the attic.
The power of the insulation technique to resist convection is dependent upon a number of factors, like insulation thickness, air circulation permeability, and temperature variation through the insulation, together with R-benefit for each inch.
two. Regarding the legality of R-20 roof foam in North Carolina: if a neighborhood code Formal approves of a thing, It is authorized. If a builder follows the functionality code, It can be attainable to setup ceiling insulation that's thinner than R-38, assuming that the effectiveness calculations present that the home's Strength price range satisfies code minimum amount prerequisites. On the other hand, if a builder follows the prescriptive code, ceiling insulation has to be R-38, in a bare minimum.
This assertion is the problem most of us have together with your putting up. You're declaring that if you do not Keep to the prescriptive code for ingredient Rvalue's your house will conduct badly.
Whilst Spray Foam Insulation is a great product for delivering an air seal and thermal insulation all in a single products, the photographs delivered combined with the Tale Evidently illustrate the flaw within their logic On This Home. The foam insulation proven is mounted to five.five inches thick in what seems to become a nominal 7.five inch deep wood assembly, there'll be a substantial degree of thermal bridging over the framing users that can perform and radiate into your un-vented attic assembly they demonstrate built.
Vermont builders usually involve a lot more roof insulation than Florida builders — not as the physics of warmth stream through roofs changes in between Florida households and Vermont residences, but because of the better delta-T. The higher the delta-T, the greater the investment decision in thicker insulation is justified.
No, the premise of my article isn't that "Except we insulate structures making use of prescriptive R-values (with air sealing straight from the source and material efficiency being equal) then somehow the composition will perform improperly."
To state that testing the material in an assembly that mimics true-world apps is fewer stringent that testing the material in isolation, indicates that you both Never understand the details or have an agenda.
I have reviewed the Icynene doc which has been referred to repeatedly all over again--The Financial Thickness of Thermal Insulation--and their Examination is very lousy. The argument about lack of BTUs for each Fourier's Law is accurate, though the attending economic Examination is garbage. They reference the ORNL research that found a fifty% reduction within the efficacy of fiberglass at very very low temperatures, resulting from convective looping inside the insulation materials. This was solved by simply layering a few inches of cellulose on best or by wrapping the fiber glass in air impermeable bags. They then use this to inform REM/charge financial Examination primarily based upon envelope leakage, which is linked to convective looping in insulation, but is definitely not just what the ORNL analyze dealt with.
Ultimate comment: at bigger thicknesses (i.e. bigger than 6"), mild density foam may become a Class III Vapor Retarder this kind of that no supplemental vapor retarder is required. This may be useful in certain conditions.
I doubt I am going to change several minds here, but normally, I haven't any difficulty recommending fewer than "code" for foam insulated roof decks around restricted attics. Even though I don't normally agree with what companies and sellers really need to say about spray foam, I can discover no fault with this particular distinct recommendation.
Suppose that you just experienced an excellent air barrier at the attic ground, a radiant barrier roof deck as well as a vented attic.....
three. At no time have I at any time proposed the local weather in North Carolina is identical to the climate in Vermont. Nor have I ever proposed that least code prerequisites for ceiling insulation really should be similar in North Carolina and Vermont.