Raising rafters?

[mitscan]

My garage is 20'W x 24'D. The roof is a 10/12 pitch. I am converting my garage into a year-round woodworking shop. The rafters have 4' collar ties in the attic. The existing ceiling joists are 2x6s, clear-spanning the 20' width. I would like to raise the joists about 2 feet to increase headroom. Doing this will move the joists off of/above the walls.The roof is supported with 1"x6" boards running from the rafters in toward the center of each side of the attic floor. Will I compromise the structure by raising the joists about 2' and otherwise leaving the construction intact? Any help much appreciated. I live in a northern rural area; there are no applicable codes and no inspectors. So, those are no help or concern. I am looking for safe and best practices. Thank you.

 

[kbs2244]

A conditional "yes"
Get an experienced carpenter to check it out.
You are going to need help "knitting" the added wall addition into the existing walls anyway.
So the sooner you get experienced help the better.

 

[Cyberbear]

Just make sure whatever you do is well reinforced and use Simpson ties where you can.

 

[Redwolf947]

There is a lot of info on the web about this. You can go no more than one 3rd the overall height of your roof. Here is one example..

View media item 60241
I did this in my garage this spring and so far its working with no issues. I sistered all the rafters from the top of the wall to the new joists

View media item 60329
Do some more research.. Take a lot of measurements. Make sure to measure between the top of walls before and after to see if anything moves.. Good luck I did this by myself..

 

[Whitworth]

Yes, you can do that. As long as you're not putting live weight on the ceiling joists (aka, using the attic for storage.) If any doubt, sister 2 by material to the rafters under your re-positioned ceiling joists. A piece of 2 by 6 from the bottom of the joists to the top plate of the wall would do fine.

 

[Falcon67]

Note that doing so increases the load on the rafters quite a bit. It also changes the outward thrust on the walls at the top plate.

http://www.timbertoolbox.com/Calcs/raisedtiethrust.htm

http://www.bobharrisdesign.com/structural/rafterTies.php

 

[mitscan]

Thanks, guys. All helpful advice. Sounds like I can make this work. Appreciate all the insights and directions.

 

[Ron_CA]

There is a lot of info on the web about this. You can go no more than one 3rd the overall height of your roof. Here is one example..

View media item 60241
I did this in my garage this spring and so far its working with no issues. I sistered all the rafters from the top of the wall to the new joists

View media item 60329
Do some more research.. Take a lot of measurements. Make sure to measure between the top of walls before and after to see if anything moves.. Good luck I did this by myself..

I really like the way you did that. By adding the extra 2x6 you were able to transfer some of the load onto the walls where it originally was instead of making the rafters carry it all.