Adding Blown Insulation To Attic

[driz]

I am planning on blowing insulation in on top of the fiberglass bats in my attic. Question is those styrofoam joist things to keep the insulation from blocking up airflow from the soffit vents. I have a 45' ridge vent running continuously along the top of the roof. How many of those styrofoam vent things do I have to put in there to get enough ventilation. Putting one in every bay would be more of a job than everything else combined. How many do I need?

[Hube]

A venting ratio for a roofed attic area would be a MINIMUM of 1 sq ft of ventilation for every 300 sq ft of attic floor area. This amount is divided equally between the soffit and the ridge vents.
example; Attic floor area 30 x 40 = 1200 sq ft
a minimum of 4 sq ft of vent is required, 2 sq ft for soffit, 2 sq ft for ridge.

Note; this is based on "free area". There are 144 sq inches in a sq ft.
A 12" x 12" opening with a 1/4" screen(mesh) cover on it would only be approx 3/4 of a sq ft because of the screen restriction. Allow for this screen restriction.
Btw, as long as there is adequate insulation, you can NEVER have too much attic ventilation.

[driz]

Ok all that mathematical stuff aside and go give plenty of ventilation whats the usual practice. Every other or every 3rd bay in the rafters. I just want to keep this as simple as possible. My place is about 50 by 28 single story nothin special but 6 big skylights.

[Hube]

The formula has been given to YOU.....
if YOU want proper ventilation, then YOU do the math.
If YOU have a tape measure, a pencil and some grade 4 school training or better, it is quite simple

[driz]

Originally Posted by Hube

The formula has been given to YOU.....
if YOU want proper ventilation, then YOU do the math.
If YOU have a tape measure, a pencil and some grade 4 school training or better, it is quite simple

And I will just leave it at that. I wasn't looking for the industrial formula, just the standard way its usually done. I know its just that simple here on Earth. I will just ask the guy at Lowes. I doubt I will have to get out the calculator. Last word, Goodbye!

[Hube]

The formula given is a RESIDENTIAL one, and it is the "standard" way.
Live and learn.

[driz]

All the square footage aside it doesn't make much difference when it all comes down to how much SF, volume or whatever is getting by those louvers or whatever they are called. Thats my question. I have little to no concern for the rest since the house comes with 12 inch perforated soffits and I had them put in 16 just to get the extra overhang. Either way I am getting at least a quarter more than it was supposed to come with. All that goes out the window when those louvers go in there and block off a good portion of the air movement. That is the real question I am trying to answer and perhaps I should have put it more plainly in the first place. I don't have a clue how much opening is in one of those bays with one of those in place. That is my real question. I have heard everything from every bay absolutely to just pull the insulation back some and plenty of air will get by , and searching moderately on the net hasn't yielded any real answers either.