During a roof replacement, the contractor inevitably realizes they have open access to your attic through the stripped roof deck. It is highly tempting for them to offer a $1,000 "add-on" to blow fresh insulation in before nailing the new plywood down. Always decline this offer.
The Airflow Disconnect
A roofing crew's primary objective is speed and waterproofing. They are rarely trained in BPI building science. When blowing insulation from above, they almost universally blow the fiberglass fast and thick, pushing it all the way to the very edges of the exterior walls.
The Suffocated Soffits
By blowing the material tight to the edges, they physically bury your soffit intake vents. You just paid $15,000 for a beautiful new roof with a continuous ridge vent, but the ridge vent cannot exhaust hot air because the roofer blocked the intake vents at the bottom with insulation fluff.
A certified insulation contractor always hammers rigid foam "baffles" (ventilation chutes) into the eaves before blowing a single ounce of fiberglass. This physically guarantees an open 2-inch channel for outside air to bypass the thick insulation and reach the ridge vent. Roofers do not carry baffles; they carry nail guns.