Raising Ceiling Joists / Rafter Ties

[CCRT]

I’m would like to install a 4 post lift in my existing garage and need 2' additional ceiling clearance.

The current ceiling height is 118.50” The garage is 24’ wide by 22’ deep. 2 X 4 wall and 2 x 6 rafters and 2 x 6 ceiling joist(all 16’ OC). The ceiling joist run front to back. My plan is to raise 7 of the ceiling joists over one bay and convert them into collar ties 1/3 of the way down from the peak.

Roof is a 6.5/12 pitch

Is this the best method (short of raising the building) of achieving addition ceiling height for my new lift?

Would sistering each of the seven rafters help?

What's the best bracket to use to reinforce the rafter to wall plate?



Any information is greatly appreciated

Thanks,

--Dave


http://djmphotography.zenfolio.com/img/v0/p324130518.jpg

http://djmphotography.zenfolio.com/img/v0/p1027329372-2.jpg

http://djmphotography.zenfolio.com/img/v0/p755172716-2.jpg

http://djmphotography.zenfolio.com/img/v0/p858070224-2.jpg

[Richard A Hetzel]

A 22-foot span with 2x6 ceiling joists?? They probably sag 24 inches! It would be good to know what region you're in, so we would know the snow load required.

What will happen if you do this is that the rafter thrust will tend to push out the front and rear walls in that bay, so that's what you need to counteract. If you could leave the first ceiling joist on the wall side, that will help, and would only reduce your overhead width to 112 inches, probably still enough to lift any normal vehicle. See that header at the top of the wall over the door? You want to keep that header from rotating and its top tilting outward, rfrom the thrust of the rafters. The more snow load you have, the more critical this becomes.

If you plan on a wall above the center, then that ceiling joist should be sistered with something like a 2x10. It won't help you at all to sister the rafters. What you need to do is tie the top of the walls together as much as possible.

You can buy inexpensive "hurricane clips" to tie the rafters to the top plate of the walls.

[CCRT]

Thanks for the info..

I'm in southern NH

There will be 1 ceiling joist left intact between the door opening and the wall.

I may be able to sister the exsisting ceiling joist on each side of the lift opening if that would help?

Worst case senerio I only need to raise the 7 ceiling joists 24" which would equate to being in the bottom 2/3 of the distance to the peak.

I was planning on a additional plywood gusset at each point where the joists have been raised.

Again I really appreciate the info provided

--Dave

[Richard A Hetzel]

Sounds good. No need to sister the ceiling joists, because they act in tension. A 1/2 diameter steel bar would do the same job. The lower you can place the rafter ties, the less rafter thrust there will be, so that would help. If you could somehow tie the top plate (if there is one) of those cripple studs up to the rafters, it might help keep that header from rotating outward.

[CCRT]

Richard--

Thanks for the great info & help.

As far as tying the top plate 2 (2 x 10's), Could i use 3/4 plywood (2' x8') from the top plate over the cripple studs to the door header or would I be better of with some steel plates?

--Dave

[Richard A Hetzel]

Well, the suggestion was from the seat of my pants, and now, looking at the photo again, I don't think there is much that will work to tie that top header back. Usually there is a double horizontal top plate that can resist some thrust. Maybe steel angles bolted to the side of the rafters and to the face of that double 2x10...something like 3x3 steel angles18 inches long, with two bolts through the rafters and two lag screws into the double 2x10...

[CCRT]

Steel thickness?

[CCRT]

Hc/Hr

24/71.5=.335

1/3=.58 adjustment factor

Current rafters are 2 x 6 X 11'-5"

Would it be a good practice to sister the rafters with another 2X6 over each of the raised rafter ties?

Thanks

--Dave

[R Birch]

Dave,

I think you’ll be OK with sistering more rafters over the modified ceiling area. If you beef up the top plates at the raised area to the inside with a couple of 2/6 or one 2/8, either against the cut off joists or maybe against the rafters if you don’t cut them off and remove them completely. It might help combat the rafter thrust that Richard H refers to. In any event I do think that time will probably show outward movement and the roof will sag. Around here we call that “Mission Style” and that’s just a little added character.

That garage looks like it used to be a carport by the way the header is installed. (?) I guess you’ll be replacing the garage door with a roll up or barn style swinger too. The typical garage door won’t work with the type lift you want to use.

And I hope that the concrete floor is good and thick too. If you have the installation instructions for your lift check the recommended specs on that. You may need more than the typical 4” garage floor flatwork. I don’t know for sure but it seems likely to me. I did a large hobby garage for a guy once and the lift area was engineered for his lift.

[Richard A Hetzel]

There is no need to sister the rafters. The steel angles could be 1/4-inch thick. R Birch makes a good point about the floor's ability to support the lift. Consult the lift manufacturer's recommendations.

[CCRT]

The floor is adequate for the 4 post lift per the manufacture's requirement.

A few more questions.

Richard,
What diameter bolts going through the rafter? Grade 8?

What section of the rafter span is compromised by moving the rafter ties up? I s it the length between the raised rafter ties and the top wall plate?

The back wall of the garage has the more conventional doubled 2 X 4 top plate. The angle iron will not work here. Do they make a standard tie for this?

This information has been extremely helpful and much appreciated.

I'm curious on this one. 2 sistered (Glued & nailed) 2 X 6 rafters would be equal to what size single 2 X ?


Thanks,

--Dave

[CCRT]

[QUOTE=R Birch;42938]Dave,

That garage looks like it used to be a carport by the way the header is installed. (?) I guess you’ll be replacing the garage door with a roll up or barn style swinger too. The typical garage door won’t work with the type lift you want to use. QUOTE]

Thanks for the info.

I don't think it was a carport.

I'll be using the existing door with additional modified tracks, longer cables and more spring tension. It will be tight but my CAD drawing shows enough clearance. The new track configuration will follow the roof line then the raised rafter ties.

I hope not to see any sagging :-(

--Dave

[R Birch]

Hc/Hr

Current rafters are 2 x 6 X 11'-5"

--Dave

I am just pointing out some numbers that don’t seem to jive within the prior provided figures.

Span = 22’

Pitch is 6.5/12

Rafter length is 11’5 (?) Is the given rafter length correct? Am I missing something?

[CCRT]

11'-5" short side (angles cut)

12'-6" over all length

[Richard A Hetzel]

The bolt diameters aren't critical. Two 3/8 diameter bolts through each of the rafters and that header should be adequate. The purpose of the angle iron is to have a connection there that won't bend, which will help that header from rotating outward. You won't need the angles at the back, if there is a double top plate. The top plate acts as a horizontal beam, and can resist rafter thrust to some degree.

I wouldn't say that any of the rafter is "compromised"...they will be as good after the modification as they are now, and if you keep the rafter ties as low as possible, they should be fine.

[R Birch]

11'-5" short side (angles cut)

12'-6" over all length

Those numbers don’t seem to fit the 6.5/12 roof pitch. How did you determine the roof pitch? (12’ 6 overall (/) including the tail?) Overall what? I don’t understand the 1’ 1” difference from top to bottom.

I will tell you that a 6.5 on 12 pitch over a 22’ span w/ 2/4 walls_plates should measure 12’ 1 ¼” on the bottom of the rafter. The same scenario with a measurement of 11’5 on the bottom of the rafters should be about 4 5/8 on 12. Even with 2/6 walls the numbers don’t fit the 6.5 pitch. The pics look steeper than a 5 pitch so I’m guessing a numbers error. (?)

(Also, your posted CAD shot shows the top of the rafter crossing the walls at the exterior plate line, or at ceiling height. That is contrary to what your photos show. Have you allowed for those differences? You should have about 4” of room not shown in the CAD pic but the pitch differences may offset that by a greater amount. Just my observations from what I can see.)

I bring all this to your attention because it appears you may have it drawn wrong in you CAD drawing and you won’t end up with exactly what you think you will. But I really can’t say it’s going to hurt you either. But, “a job well planed is half done.”

[CCRT]

I measure at the underside of the roof.

http://djmphotography.zenfolio.com/img/v0/p945351219.jpg


"CAD shot shows the top of the rafter crossing the walls at the exterior plate line, or at ceiling height. That is contrary to what your photos show. Have you allowed for those differences? You should have about 4” of room not shown in the CAD pic but the pitch differences may offset that by a greater amount. Just my observations from what I can see.)

I took the rafter lengths off the cad drawing (the rafter / top plate placement may have caused the discrepency). I drew it this way to build in some clearance cushion. (worst case)

I took a closer look at the rafter top plate connection and the rafter's bird mouth places the bottom edge of the rafter about 1.5" from the inside 2 x4 face.

Thanks for bringing alll these issues to my attention.

--Dave

[my2nd40]

Try this site.....this is the way I did it.
http://www.sammemmolo.com/sams_garage_2.htm

[CCRT]

Sam--

That's a great idea.... Great Photos!

Any chance I could have your E-mail to get some details.

You went with the BYB lift Right?

Thanks,

--Dave
http://home.comcast.net/~ccrt-racing/ccrt.htm

[Don_P]

Whoa, get an engineer to check that. The rafter (top chord) span has changed and the bearings are changed also. I'd exercise some real caution.

[my2nd40]

CCRT, those pics are from Sam Memmolo's website. Sam is host of "Two Guys Garage" on the Speed Channel on TV. I raised my ceiling exactly like he did in the photo's with minor changes, I used I Beam where he has round pipe, and I used some factory made bar joists I had left off of a building project our company did. I've encountered no problems at all after two years and expect none. And I did buy a Backyard Buddy lift, which is a quality piece of equipment.

BTW.....I am a graduate engineer, not that it matters.

[CCRT]

So it looks like the bar joists were sistered to the existing joists and one was used as a ridge beam. My ceiling joists are 2 X 6. What height bar joist would be used?

They must have special ends / brackets to tie them to the top of the wall plate?

What's a ball park cost of 22' bar joist's? Lets say 2 X ? X 22.

I was thinking the same thing of using 4 X 4 instead of the round steel.

This a very interesting option if the cost are not too large.

Thanks,

--Dave