Roof Repair for Cinderblock Garage (Top Plate & Joists)
We recently moved, a few months ago, into a 100 year old home; extensively renovated 10-12 years ago (we are the 2nd owners since the renovation). I am unsure how old the garage is, or when the existing roof was put up -- the south facing side has been updated with OSB, while the north facing has the (assuming) original slats.
I have two main issues with the roof that I would like to address:
Top Plate Dry Root
There is some dry root in areas of the top plate. You can see some of it on the far left of the attached "photo.jpg" image. I would like to replace the top plate in the effected areas!
What would be the best way to support the roof so that I could remove the existing top plate and replace it with a new one?
How should I go about securing the top plate to the cinderblock walls?
Joists & Collar Ties
About half of the joists appear to have been removed and replaced with a support higher up on the rafter -- I'm unsure if it would be considered a "collar tie" or just a "really high joist". You can see the some of them in the "photo_02.jpg" attachment.
Would replacing the remaining joists in this way compromise the structure? If so, should the joists that have been replaced, be returned to their original state?
Also... what the heck is up with my Frankenstein joist!? You can see it in the "photo.jpg" attachment. It is several pieces of wood spliced together to form what might be called a joist. I'm not sure why it just wasn't replaced.
Does anyone have any ideas why it is this way, and why I couldn't just go ahead and replace it with a new joist (be it at the same height, or higher)?
Thank you for any advice!
EDIT: Sorry about the second image. I'm not sure why it flipped, but it is obviously upside down.