foam channels for rafters

[mmg]

As I said in a previous post, I'm having more insulation blown into my attic to augment the two very sad inches of batt insulation that is already there. As an aside, the previous owner actually bought new ceiling tiles and layered them between the joists on top of the insulation in a feeble attempt to increase the R value. So I really have 2 3/8 inches of insulation :roll:
So, I know I have to put up those foam channels to keep the soffit vents open, but I was under the impression that these had to span the rafters, not just go inside them.
I was reading Guido's post (the one previous to this) and saw the pictures he attached of them being installed inside the rafters.
Won't the blown-in insulation still find its way onto the soffits?
Apparently I have to push these foam channels right down against the soffit. I just didn't envision that providing enough air flow through the soffit vents.
Your comments would be greatly appreciated.
Thanks.

[deejoe]

In most normal soffit/attic installations the rafter baffles "chutes") are installed up tight to the undersides of the roof deck.
A wad of insulation is then placed under this baffle and jammed onto the top plate in order to block any attic insulation from entering this soffit 'void'.
This procedure allows the soffit intake air to come in unhindered into the attic ares ,rise and go out the high openings 9either mushroom caps or ridge vents.
The ratio for attics is a minimum 1 sq ft of free vent area for every 300 sq ft of attic floor area. (divided 50/50 between soffit and ridge vent areas.)(the more the better,as long as an sufficient R value is in the ceiling (below).

[mmg]

Thanks deejoe.
I'm assuming I have to do this at every rafter space regardless if there are soffit vents directly below a particular rafter ...am I right? Otherwise I'm guessing the insulation would still find its way down the soffit void.

[RobertLangDirect]

Do you have a link that shows what you described? Seriously, I am interested in looking at this, w/o climbing into my attic, thanks!

Robert

[mmg]

I'm not sure if you mean a specific diagram of what deejoe was talking about, but if you look at the post in the forum started by Guido and titled "this is what my attic insulation looks like", you will find a picture of the baffle installation of page 3.
What deejoe was explaining was that I would also have to stuff some batt installation between the base of the baffle and the top plate to prevent the blown-in stuff from getting into the soffit space.

[deejoe]

If you have continuous soffit, then all the rafter spaces between the top plate and roof sheathing have to be blocked in order to stop any insulation from going into thissoffit area.
These channel baffles, wherever they occur, also have to have to be blocked from the top plate to the lower part of the baffle.
This now means that all the lower soffit is a "big plenum"and any incoming air will now enter only at the channel baffle points .This incoming air will now rise and circulate out the higher exiting vents.

In place of the foam baffles, plwood, osb, styrfoam pieces can be used, but these "channel type baffles" are not expensive and are more easily installed.

[Guido]

Here is the best image I found. Hope it helps.