What size for rafter ties?

[tstaude]

This weekend I have to put up rafter ties along with the rafters on half of my barn. the front rafters are 2x6 and the rears are 2x8.

the rafter ties will span about 24 feet and I am having a tough time selecting what to use.

They will be bolted at each end and end up under tension.

To my surprise 2x6x24' are available locally, but I feel like these might get saggy.

My other thought is to run 2x8x~16' overlapped and doubled up the full 24' length.

I have to build 5 of these for my span.

Below is a picture of the first half which has a 2x10 deck that ties it all together

 

[Bert_]

Are you putting a floor up there? Kinda looks like you intend to.

If no floor above then 2x6 is fine. You want to drop a 2x down from the peak to the tie. That will break it into (2) 12' spans.

 

[sjvicker]

Since its tension is using cables an option?

 

[Half-fast eddie]

Since its tension is using cables an option?

Agree. Cables, chains or steel rods, with turnbuckles.

 

[tstaude]

the half I am doing this weekend is wide open aside from the rafter ties.
I had given thought to the cable idea, but kinda want to stick with bolted wood.

 

[PoorUB]

Clear span of 24 feet? Even a 2x12 will sag!

If you do like the other post says and run a vertical up to the peak in the middle then a 2x6 would be fine.

Clear span? I would look at I-joists.

 

[Bert_]

the half I am doing this weekend is wide open aside from the rafter ties.

What does this mean? Is it just going to hold a ceiling or are you putting a floor up there and using it for a room.

Going to be very different if you want a floor.

 

[firebirdparts]

2 by 6 will do the job for 24 feet. You can't hang a ceiling on that. That is just for tension. I'm sure that's what you meant. 2 by 8's on 16" are just marginal for a ceiling.

 

[tstaude]

the side with the rafter ties has no second floor, they will just be there for tension and may hold the garage door rails.

I am going to go with 2x8 to be safe for supporting the garage door rails

 

[Bert_]

the side with the rafter ties has no second floor, they will just be there for tension and may hold the garage door rails.

I am going to go with 2x8 to be safe for supporting the garage door rails

2x8 is really unnecessary. You can break it up into (2) 12' spans very easily by dropping a support down from the peak. You could even break it up into 8' spans by building it like a w truss

 

[Bretny]

Clear span of 24 feet? Even a 2x12 will sag!

If you do like the other post says and run a vertical up to the peak in the middle then a 2x6 would be fine.

Clear span? I would look at I-joists.

I would do this also. Vertical in the center to the roof and use 24' lumber. If you wanted to add even more you could put two 45* boards out from the center to attach to the roof rafters.

Eventually you will add some stuff up there..and more stuff so going with something bigger than 2x6 would be my choice. 2x8 or 2x10 also gives you alot of nailing space on the rafter at the ends.