Ceiling/Rafter Raise Calculation

Job ID: 32951150

Budget: $10 – $30 USD

We are looking to raise an existing ceiling height.

We currently have rafters (which I think are 2x6 rafters @ 12" o/c) with 2x6 cross-bracing/Ceiling Joists (at around 24"o/c).
Every over rafter (alternating with the 2x6 cross-bracing) has a 1x6 cross-bracing higher up.

Height from floor to ridge is around 13ft.
From bearing wall to bearing wall - span is around 23ft.

(See attached images for clarity)

We need to know - how high can we raise the cross-bracing/ceiling joists?
What is the connection from ceiling joists to rafters?

We can provide new cross-bracing/ceiling joists 2x6's (or 2x8's) every rafter, if needed. - Any extra height we can get will help.

I need structural detail and a calculation.

Thank you!