[Willie T]

Just a guess, but since this is a garage, I would suspect that these 'ceiling joists' were held low like that to give room for storage above them. Shouldn't hurt to raise them. But 20' is a heck of a long way to span with only 2x8's if you are going to store anything up there.

But do NOT consider eliminating them. They are ties between the two walls, and need to be there to keep the rafters from shoving the walls outward. Move them one at a time, not all at once.

In my garage, no ties were put in place. The roof ridge began to sink over the years. I jacked up the ridge in a couple of places, and installed steel cables across where your rafter ties are... except that they were installed through small holes drilled in the rafters, themselves. The cables have turnbuckles, and I just tightened them up till there was no weight on the jacks. Then I removed the jacks. That was 25 years ago, and all is still well. (BTW... I could use only cables because we have no snow loads down here... so 'tension' only, was needed. Up North, you need both tension and compression. Thus, you use lumber, not cables.)

This gives you an idea of just how much work those ties are doing for you right now.

 

[Willie T]

Yes that is exactly what they are there for. At least that's what I'm assuming. I just pulled down a bunch of old stuff from up above there. So, with that being said, do I even need the joists there as they are?

Jesse

Yes, yes, yes! YOU NEED THEM. Do NOT eliminate them. They serve a very serious structural purpose. (See my other post)

THIS may give you some better understanding of the importance of rafter ties, collar ties and trussed rafters. Pay careful attention to the use of the words RIDGE BEAM in this article, as opposed to RIDGE BOARD. VERY important that you understand the difference.

 

[Willie T]

Ok that's what I thought. What other post of yours are you referring to?

#4 in this thread.

Some things have been added to my posts since I first wrote them. Re-read them to be sure you miss nothing. This is important stuff. Roofs CAN and DO fall in from being incorrectly altered.