Roof Repair for Cinderblock Garage (Top Plate & Joists)

Boiler98

Hello all.

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.

Attached Thumbnails

   

stuart45

Wall plates used to be bedded on mortar and the weight of the roof held them down, but nowadays straps can be an added fixing.

joecaption

There really is no such thing as dry rot, that roof leaked or is leaking.
It also looks like fungus growing on some of the rafters, fungus eats the cellulose that holds the wood fibers together. I'd try sticking a screw driver in the rafter to see if there punky.
No clue why the ties were done that way, would have worked with just the ties nailed to the sides of the rafters.
I wonder if that 4 X 4 set up was but there to attach some form of chain fall to lift something.

stuart45

Could be that they needed extra headroom.
Collar ties should usually be in the bottom third.

Boiler98

Thanks for the input, all!

I'll check out any issues with fungus this weekend, and look into straps for the top plate. Stuart, do you have links that talk about installing straps when replacing a plate?

I'm also wondering what the best way to support the roof while replacing the plate would be.

Thanks!

stuart45

Sorry, I can't find a link, but if you look at the photo of one you can see that the are screwed to the plate and the wall.

Adjustable props can be used under the collars or joists to take the weight.