What is the roof raised heel height for R-60 insulation value?
alumniu
| Posted in Energy Efficiency and Durability on
What is a typical heel height to achieve R60 insulation value?
Wondering opinions on a somewhat standard height that I can tell my truss manufacturer. And what type of insulation you achieve this value with….blown-in cellulose, fiberglass, etc.
Thanks!
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Replies
The short answer: 20"
Cellulose would perform at ~R60 at settled depth of 16-16.5", but the initial depth has to allow for ~10-15% of settling, ergo 18-20". The 20" number the recommended initial depth for R60 some of the better fiberglass blowing wools too.
http://www2.owenscorning.com/literature/pdfs/10011287AttiCatManufacturersFactSheet.pdf
http://nationalfiber.com/docs/CelPakSpecSheet1209.pdf
R60/3.5/in = 17.14", go 20" heel to allow for venting baffles.
For blown cellulose, you need 18". So you'd need at least that much clearance above the conditioned space, plus a gap for airflow just below the roof.. Your truss design depends on roof pitch, eave depth, etc.
Loose fill cellulous has an R-value of 3.7/inch so you'll need approx. 17" to hit R-60
http://www.bpiexamacademy.com/1-appropriate-insulation-applications-based-on-existing-conditions.html
Adam,
The answer depends on the type of insulation you will be installing.
Here is a link to an article with more information on the issue: How to Insulate an Attic Floor.