Attic baffle height
I’m going to be blowing in cellulose into my attic. I’ve installed ventilation baffles, but I’m wondering how much cellulose I can add? How much higher does the top of the baffle need to be compared to the level of the loose cellulose? Thanks. -Andrew
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Depending on truss design and roof pitch, you can often get to R-60 with a single course of baffles. If you're careful, you can bring the material up within a few inches of the tops. The trick is to minimize the amount of airborne material so that you don't clog the baffles. I like to keep the hose buried so that it gradually pushes the material up from below. Expect 10-15% settling, after which the tops of the baffles will be well clear of the material.
Baffles are usually inexpensive (although admittedly they can take a while to install). If your baffles are a little short, I would hate to hear that you decided to install less insulation that you wanted, just because of a small error in your baffle height.
When in doubt, you want to go a little deeper with your insulation. If you are right at the margin, install longer baffles so you can go deep with the cellulose.
I measured the height of the baffles. I can get R60 and still have at least 2 to 3 inches of clearance. Is this adequate clearance? I think I'll also point the hose down into the material like Jon says to minimize future settling.
It sounds like you are good to go -- as long as you plan for the fact that the cellulose with settle 13% to 15%.
If you are assuming that you need 16.5 inches of settled cellulose to achieve R-60, you should install 18.5 or 19 inches of cellulose.
For more information on this topic, see How to Install Cellulose Insulation.