Does anyone have a calculation or guide you follow to de-rate the r-value of existing insulation?
I'm familiar with RESNET grading, but that seems to be for new installs and I can't find what the actual calculation would be - I'm assuming it's built into modeling software, but does anyone know what the actual adjustment factor on the R-value would be if rating something Grade II or Grade III?
I'm interested in this information both for batts and loose-fill.
Any resources (even tangential) are greatly appreciated!
Page 7 & 8 of the old Technical standards have that info. (attached)
Ah, the table on batt insulation was what I was thinking of but couldn't find. Thanks!
You are welcome. Not sure what that did not make it into the new standards, but I still use it myself, as do many others I know.
I've attached the HES insulation derating page for illustration.
You can find an assessor or train to use their software. It is a simple certification.
Attached HES insulation derating file.
Check the California Installation Standards with a well thought out and researched listing of old insulation.
Open batt or open fiber will wind wash in vary cold weather so the batt says R-30 and with IR its says R-10 test same spot with out wind and is R-30. How do you deal with wind washing?
I don't have a copy of the original BPI charts, but I believe our local utility has adopted the original charts and included some examples of insulation in various states. You can tell which portion of the attached was produced by the utility as they are have the logo attached. The following pages that do not have the logo are the original insulation rating charts that came from BPI.