Cellulose Insulation Moved by Wind
albertoarriaga33
| Posted in Energy Efficiency and Durability on
We’re prepping a house for blown in cellulose insulation and during inspection we noticed a lot of wind coming into the attic space. We’re worried that this wind can move the cellulose out of place and leave hot spots. The wind is coming in through the metal panel ridges at the fascia.
What would be the best way to block high winds? Were not looking to fully air seal rather just stop high wind movement. Im thinking fiberglass batts at the perimeter as we would like to avoid foam.
Thanks!
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Replies
I would build some air dams. It's common to build the air dams with 1/2" polyiso, but you can also use cheap panel products like 1/4" plywood or OSB. I have used 1/4" "waferboard" for this purpose in the past. Waferboard is like a non-structural version of OSB, and it's usually the cheapest thing that will work here. I would double check pricing though, since with today's crazy materials prices, you might find some kind of plywood is cheaper than waferboard. The goal is to get something stiff enough to work that is cheap and use that to build your air dams since they don't need to be very strong, and they don't need any particular structural grading. When I've built these in the past I've used a combination of 1/4" waferboard and 1x2 furring strips along with my finish nailer. It goes pretty fast since you're working with entirely lightweight materials.
What you're trying to stop here is known as 'windwashing' and fiberglass alone won't stop the air movement. You get degraded R value from the air movement too, and it's especially a problem out at the eaves over the top plates for exterior walls. There are ready-made baffles that you can use between rafters out at the eaves, which is another option. All you need to do is use baffles and air dams to direct the airflow up above the level of your attic floor insulation and you'll solve the problem -- you don't need to go much above the level of that insulation. You also don't need to air seal the baffles, just do a best effort of cutting them to fit and press them in place and you'll get very nearly the same amount of improvement as you would if you sealed everything with caulk.
Bill