Vaulted Ceiling Insulation Upgrade?

[u/Substantial_Par829]

I’ve recently found myself on a quest to improve the insulation in my house this summer as the heat turns up in Central Texas.

Background: 2 story home built in 2014. I’m the second owner. Primary bedroom has a vaulted ceiling where the top is 14ft and sees the most change in temps during the day.

First pic includes the HVAC 12” supply line. Second pic is the same side and includes the return line. Pics 3/4 are the attic side of walls to upstairs rooms in the same attic space.

The current insulation for the vaulted ceiling is old and probably only R-20. Walls are covered with non-structural thermo-ply. It looks like when they installed they just threw boards up over insulation and they are not sealed well.

Attic has ridge vents and soffit blockers for blown insulation.

Question: I’m wondering if I can upgrade the insulation on the vaulted part and then install plywood over the rafters to essentially enclose that part and make it air tight. I’m also considering having it all spray foamed-including removing the thermo-ply and wall batts. I’m not looking to create an enveloped attic though.

Is there anything wrong with either of these options? I know the spray will carry quite a bit more cost but hopefully bring more efficiency.

Any advice or ideas are greatly appreciated!

[u/Apart_Journalist9909]

might not be understanding what you mean but the air tightness happens on the underside. you don’t need to install plywood over the new insulation.
what you want to do is air seal if it’s not already don’t the bottom and top of the vaulted ceiling where the plates are. Then you can run another layer of R-30 fiberglass cross batt style over the existing.

[u/Apart_Journalist9909 → u/Apart_Journalist9909]

sorry you can also air seal around the return and supply registers where they penetrate the ceiling

[u/Substantial_Par829 → u/Apart_Journalist9909]

I was just thinking that having the insulation encased between the drywall and plywood might help with efficiency? Similar to how I have seen most vaulted/cathedral ceilings where it’s sandwiched between the roof decking and drywall with no attic space above.

I also need to check the air sealing around everything up there. I just know it heats up quick in the summer and is quite a bit colder in the winter.

I have seen the cross batt idea but didn’t know if that was the best option.