i've got a 2 car detached garage that I'd like to pull a little more head room out of by raising the rafters, I've heard of this being done successfully before, but I dont know much about it. I've read somewhere you can raise it as high as 1/3 of the total peak.

 

Currently, there are only (3)Three 2x6 rafters going from end to end. Were these likely there to hold the walls together while building ?

 

Anyway, here are some pics I took when I moved in years ago.

 

 

What you call "rafters" are actually rafter ties. They keep the sidewalls from bowing out if you have a non-structural ridge (the board the rafters are attached to at the top). Rafters are the angled framing members supporting the roof substructure.

 

Your 1/3 calculation is correct. You can raise them up 1/3 of the height from the wall top to the bottom of the ridge.

IMO, they are still holding the walls together.. I'm not an engineer, but the wooden* roof would put downward and outward pressure on the walls. Think about removing the base of a triangle and where the directional force of the weight wants to go. The roof wants to go down, and the only direction for the support beams is to go is out.

thanks for the term correction rightisright, Jack, I would figure the same thing, but I hardly passed geometry in high school so Im not 100% sure.

 

 

Rightisright, So do i have a 'non structual' ridge? thanks

 

Even though raising them up 1/3 SHOULD be good, I'd leave two at the height at the very ends , well front and back in my case. Right up against the walls. Doesnt really get in the way of headroom, and might make me sleep better at night, Is this something I should consider worth while? Or dont even bother.

 

-alec

IMO, they are still holding the walls together.. I'm not an engineer, but the wooden* roof would put downward and outward pressure on the walls. Think about removing the base of a triangle and where the directional force of the weight wants to go. The roof wants to go down, and the only direction for the support beams is to go is out.

 

If the rafters are properly connected to the top wall plate, raising the ties 1/3 of the height won't cause any issues. Now, the ties MUST be properly fastened to the rafter. Nails won't do it here because when the rafters deflect under load, there will be significant pressure placed on the connection point. I would use two 3/8" or 1/2" carriage bolts at each connection.

thought about added these to the (angled) rafters as well, thoughts?

 

You should put those on the rafters that the ties attach to because there will be more load on them once you raise the ties.

 

Current building code calls for all rafters to have a positive metal connection between the rafter and top wall plate. IMHO, it's overkill in our area (but not in hurricane/tornado prone areas).

Thanks, and what do you think about leaving ( moving) 2/3 ties to the very ends against the front and rear walls for additional support? Waste of time ?

When I built my second garage the building inspector asked me why I did everything 12" on-center and used all those metal plates to tie it together. I told him I didn't want to ever worry-about anything coming apart. It's been through two hurricanes so far and I haven't even lost a single roof shingle!

Thanks, and what do you think about leaving ( moving) 2/3 ties to the very ends against the front and rear walls for additional support? Waste of time ?

 

If you put them right against the walls, they won't really accomplish anything. The double top wall plate and the sheathing hold that part of the structure together.

 

If your walls are currently plumb and your roof ridge has no noticeable sags in it, keep the tie spacing the same as it is now.

 

 

Rightisright, So do i have a 'non structual' ridge? thanks

 

 

Yes. If you took away the rafter ties, your walls would bow out and the ridge would sag.