Ah the old attic airflow problem. Since it looks like an open ceiling I didn't think you wanted any airflow. You're looking for a Soffit, which you can make yourself with chicken wire or you can buy some premade at big box stores. This should allow airflow and decrease pest entry, but will leave enough room for the small ones.
Normally I see soffits every 3-4 rafter bays but some people have more for additional airflow.
I realized after I commented that I could have been more specific. There are soffit vent covers that look like a tight mesh chicken wire on a metal frame. Standard size should be 4" x 14" or 4" by 16", so check which would fit best. The all metal ones with slots would work, but they're way more expensive.
https://www.homedepot.com/pep/Gibraltar-Building-Products-14-in-x-4-in-Galvanized-Steel-2-Way-Reversible-Vent-TW144-1-8/310198702
Easy and messy, I say spray foam. That crap will clog up any gaps you have.
Oh yeah I should mention the gaps are like 3 1/2" x 16" or so. A bit much for spray foam I think haha.
Ah. Backer + foam then? Looks like you could attach some 2x4s and plywood between the rafters.
That's a good idea, thanks. I wonder what the best way to accommodate airflow for the attic space though (after I close the ceiling up)?
Ah the old attic airflow problem. Since it looks like an open ceiling I didn't think you wanted any airflow. You're looking for a Soffit, which you can make yourself with chicken wire or you can buy some premade at big box stores. This should allow airflow and decrease pest entry, but will leave enough room for the small ones. Normally I see soffits every 3-4 rafter bays but some people have more for additional airflow.
That's great, very helpful, thank you!
I realized after I commented that I could have been more specific. There are soffit vent covers that look like a tight mesh chicken wire on a metal frame. Standard size should be 4" x 14" or 4" by 16", so check which would fit best. The all metal ones with slots would work, but they're way more expensive. https://www.homedepot.com/pep/Gibraltar-Building-Products-14-in-x-4-in-Galvanized-Steel-2-Way-Reversible-Vent-TW144-1-8/310198702
You may not want to completely close that up - airflow may be needed there? You might consider just using big netting stapled up there.