Attic Inspection

I have a couple of questions. I’m new to the business and have been going over the online classes. I live in the STL area and have a situation with a newer home.
As built, (2009), The 4 car garage is attached. There is access, from the garage and also inside of the home, to the attic. Where the garage and attic meet, the builder cut a large open area between the home portion and the garage. The rest of the area has covering. The garage isn’t insulated and the attic has 9 inches of blown insulation. This is a open home with 12’ ceilings.
In the evening (summer months) it’s hard to keep cool in the area’s above this large opening. In the winter month’s its colder on this side of the home.
I discussed with the home owner about insulating the garage area and also the front porch area. It’s the same way. No insulation and also open to the attic with the only seperation being the vinyl covering for the porch.
Should these area’s be boarded up to isolate them from the attic? My guess is yes.
Is this a flaw in the construction, as all of the homes have been built this way (as I’ve seen in this subdivision)?

(See red above) My first question is… did this compromise the firewall seperation between the house and the garage???

Yes, would be my 1st response. But I believe the right answer is No. The garage has sheetrock on all walls and also on the ceiling. There is a access hatch to the attic in the garage and inside the home.
The sheetrock is the fire barrier between the garage and the attic/home.

Since there is access from both sides, have the wall repaired for the fire seperation, and insulate the home side of same wall with rigid board. That may solve the cold issue as well as the breached firewall in one stroke.

One product will stop everything and does not cost an arm and a leg. Make sure all the buts and joints have tape and mud. Recommend Insulated ceiling and hatch with Roxul.

Great for sound proofing to.

The attic and the living space should be air sealed from one another. I would suspect that there is either a lack of insulation in a wall or there is an air movement issue. When you say 12’ ceilings are all 12’? Even the garage where it connects to the house? Why I’m asking is if you have a 8’ ceiling on one side and a 12’ on the other side of a wall there there can be a large issue with the thermal boundary.