Insulation, Radiant and Vapor Barriers - Soffit Baffles?

I'm preparing to blow cellulose into my attic and as I'm getting everything right for installation, I'm now to the point that I need to consider baffles for the soffits.

Throughout the history of this 55+ year old house, the only attic ventilation has been the screen-covered square gable vents, up near the peaks. As I've been working on the place, I've added some soffit vents, but I haven't done anything to most of the soffits because they didn't need any work themselves and because a lot of my roofline just wouldn't be conducive to extensive, anyway.

I've yet to go down to the local building supply to ask about soffit baffles. My cellulose was special order, so they don't ordinarily stock it and I doubt they have special (cellulose-specific) baffles on the shelves, plus they didn't try to sell me anything, back when I bought the insulation.


I'm going to have to rent a blower from one of the box stores and the one closest to me stocks Accuvents from Berger, which according to the <A HREF="http://www.bergerbuildingproducts.com/productsAccuvent.html">website</A> looks to be ideal for the areas where I've added the soffit vents, but they're a little expensive to put the whole length of the house, where incoming air isn't a big concern and where I'm mostly just trying to keep my cellulose from going down into a void.


Thinking in my own mind, I'm wondering about cutting blue styrofoam into blocks and standing them between the joists along the extreme outside edge of my roofline, or maybe cutting "bitemarks" into a length with them straddling the joists and bridging the rafters.

I guess my first question is whether this sounds like a good idea and if so, I should ask whether there'd be any measurable benefit from using 2" polystyrene rather than the 1" width?

As some may have noticed from one of my previous posts, I've bought a bunch of 2" that I'm slowly working around my crawlspace, so I already own quite a bit, but if the potential benefit might be negligible, I could consider buying just enough 1" to put around the perimeter of the attic.

(I'm thinking that the 2" is more rigid, so it'd be easier to push into place and I already own a lot of it, but the 1" is half the price and since it'll be faced the entire depth in cellulose anyway...)


Any advice, knowledge or experience would be appreciated;
And as always, thanks in advance.

They generally recommend one to two inches of space above the blocking you are proposing and same between the insulation and roof sheathing. Small notches and small holes don't move a lot of air.

One vs two inch blocking will make little difference. Primary benefits are, as stated, keeping the cellulose out of the soffit and reducing the wind washing on the end of the insulation. Cellulose is much less susceptible to the wind washing. Make sure you get the blocking out far enough so the insulation covers the top of the wall, a common area where the thermal bridging is noticeable.

Not sure how strict they are in your area, but technically speaking, most rigid foam must be covered with a fire barrier. I know living space and basements, not sure about attics. Wouldn't want to have you get it all in and have an inspector come along and #%*!.:wall:

Air seal what you can before you blow in the insulation. Cellulose does a good job of blocking air flow, but extra sealing can't hurt and difficult to go back afterwords.

GL
Bud

Not sure how strict they are in your area, but technically speaking, most rigid foam must be covered with a fire barrier. I know living space and basements, not sure about attics. Wouldn't want to have you get it all in and have an inspector come along and #%*!.:wall:

Humm... good question.

I assume that they must be listed (like some rigid foam insulating materials) for exposed installation in such locations, I'll see if I can find out.

Maybe I'm not getting the entire picture, so forgive me. Why not use Owens Corning insulation baffles? They are made for the situation you are describing. You install them down to where the rafters touch the plate. They stop the insulation from going over into your soffit area and provide air movement from the soffits to the general attic area.

They generally recommend one to two inches of space above the blocking you are proposing and same between the insulation and roof sheathing. Small notches and small holes don't move a lot of air.

Theoretically, one would think that there's not a lot of air coming from the closed, unvented areas of the soffit. Sure, there's probably a small crack between the facia and the soffit or the fascia and the roof deck, but that probably wouldn't amount to a lot.

I'm not opposed to the idea of leaving some space between the top of the block and the roof deck, but that also sort of works into my request for clarification concerning this next little snip.


Make sure you get the blocking out far enough so the insulation covers the top of the wall...

My original idea was to put the foam blocks along the top of the vermiculite-filled cement block walls, but if I'm reading this section correctly, you're suggesting that I push the foam blocks down into the soffit, beyond the walls, so that I have cellulose filling the area above the concrete block.


Not sure how strict they are in your area, but technically speaking, most rigid foam must be covered with a fire barrier. I know living space and basements, not sure about attics. Wouldn't want to have you get it all in and have an inspector come along and #%*!.:wall:

My permit doesn't list attic insulation as a required call, so I'm not exactly sure if you're referring to the building department or to a home inspector (Michael?), when I offload the place down the road.

My local inspector (the whole building department) told me that I'd have to call him out, when I frame-in the skylights (in another part of the house) and framing ("prior to lathing and plastering, duct work, fire stopping and other equipment is concealed") is listed on the back of my permit as a required call, but I hadn't intended on calling him for the attic insulation.

Since we're also planning to redo the electrical over the next few weeks, I'm thinking that he'll want to peek into the attic to look at the wiring, so he will be able to see the insulation, but I hadn't intended on calling him for this particular part of the job.

Oh, and as Ed points out in several posts, if you search on this forum on the word cellulose, the blown-in insulation is supposedly fire-proof. Though, I don't think that I'll try melting a penny in my hand, as it is suggested that he's done.


And finally,

Air seal what you can before you blow in the insulation.

When I originally posted this query, I thought that if my foam block idea passed muster, I'd probably have to come back to ask whether I should spray foam around the polystyrene, but all of my questions about the 1" gap and whether I should push the blocks down into my soffits seem to also have some bearing on this part of the question.

Right now, my downward-sloping soffits are mostly two-feet deep. The previous owners, who built the house just laid-down batts of R-11 and stopped at the walls. I'm thinking that if I don't put some kind of blockage over the end, then I'm going to risk losing quite a bit of cellulose down into these holes, but my wife, who also has no experience with the blowers thinks that whatever might work down could be worth less than the effort that blocking them would require.


Again, any thoughts, advice, knowledge, experience, clarification or whatnot would be appreciated.
I'm getting a late start today, but because I've bathed my attic in light, my day has just begun.

Thanks.
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ETA: Chandler, you responded while I was composing this reply.

As I do the math, it'd cost more than $120 to install the Accuvents all the way around this section of my house. Compared to the $2000+ that I've spent on insulation, $120 doesn't seem like a lot, but I've also called my local building supply and they stock no type of preformed baffles, whatsoever. So, anything purchased would also require a 200 mile round-trip to the next building supply house (a box store).

Maybe my local store could get something on their daily truck from their warehouse, but when I called, the experienced fellow who was transferred the call from the inexperienced CS rep didn't volunteer anything under the generic heading of "insulation baffles - to keep the insulation out of the soffits".
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2nd ETA: Now that I think about it, I can recall specifically listing blown-in attic insulation when I was getting the permit for my re-roof. At the time, the guy (the only guy) said that a permit wouldn't be needed for that part of the job. My re-roof only needed a permit and no inspections, so if no permit is required for attic insulation... Though again, he will need to go up there to inspect the electrical...

Thanks and double, triple thanks for all of the help!