Soffit Vents

[Semon]

I just had insulation blown in the attic space and am about to put new soffit and fascia on.
I want to put vents at the suffix end of the roof the Styrofoam ones.
Do I need to put one between each trust or every other one?

[Smooky]

Use the foam or plastic baffles between all of the rafters or trusses. Also make sure the insulation is not blocking the soffit vents so you have good air flow up to the roof and out ridge vents etc.

http://inspectapedia.com/interiors/Roof_Vent_Baffle020DFs.jpg
http://www.countryplans.com/images/gr9-insl.jpg
http://i252.photobucket.com/albums/hh21/mrbear3800/House%20related/kneewallbaffles.jpg

[Dana]

Usually you'd want to put in the rafter baffles BEFORE blowing in the insulation, since putting them in after the fact is a dusty/itch PITA.

Be sure to clear the soffit vent holes completely, and backfill the insulation evenly or you'll get cold spots (sometimes even condensation on very cold days) on the edge of the ceiling in winter.