The Forestry Forum

I am cutting the rafters for our coach house that we are going to live in while we build the main house https://forestryforum.com/board/index.php?topic=15403.0

While doing the layout last night I noticed that I forgot to specify the placement of the collar ties on the rafters (how high they should go).  It is a 6-12 pitch with the rafters spanning (building width) of just under 22 feet.  We are using SYP and the rafters are 8x8 and the collar tie is 6x6.  I would like them as high as possible since there is a small storage loft between bents 4 and 5. 

Thanks

Joel

Designing as you go isn't the best method.......

Although it is sometimes called a "collar tie" it has been proved by structural analysis that it only "ties" the rafters together when this beam is within a foot above the plate.
Collar beams usually hold the rafters apart and prevent them from sagging from roof load in or near the middle of their length.
If you want to have some storage space make them high about one third down from the top.
The closer to the middle the better.
If there is enough room you could place short queen posts between the tie and the rafters to help support the lower third of the rafters.

Some thing like this:
(https://forestryforum.com/gallery/albums/userpics/10095/Northviewframeandfoundation-s.JPG)

only further up for the collar beam and further apart for the queen posts, so that the collar connects to the rafter down 1/3 in elevation and the queens connect to the rafter up 1/3 in elevation.

This is a workshop that is 20' wide and with a 6/12 roof pitch.

Good luck with your project.

Jim Rogers

Jim,

Thank you for the quick response.  After my post I was looking through my books again and saw mention that the ideal position was in the middle of the rafters.  My plans have been done for a while and stamped etc.  Late last night I was getting ready to cut the mortises for them and noticed that they were located in the middle of the rafter on the plans but the actual distance was not noted.  Tried to call my engineer friend who helped with the plans and stamped them for the county but he was not available.

I guess I was in a second guessing mode or in a brain freeze especially since I am working in the virtually unheated lower level that will be the fountaion for the frame.

I"m glad to hear you've got a fairly good set of plans, that is approved and stamped.
Now if they had all the dimensions you'll need that would make them a great set of plans.

My comment: "Designing as you go isn't the best method......" is an educational comment to all who will read this thread in the future.

Jim Rogers

Jim,

You are correct about designing as you go.  However, last night when I test assembled my first two rafters to check to make sure that I calculated the pitch and rafter member length correctly to get the right span I realized that storage loft above one of the bents was not going to be very useful so I decided to forgo that and have the open ceilings in that section too.

So I guess that would fall under "modifying as you go" instead of "designing as you go".

Joel