Hip roof help

[oxmanwi]

I have a hip roof on my 3.5 garage. I have a 34' long pieced together Cross support 2x4's spanning the width of the garage resting on the ceiling joists. What is the point of this guy and is it part of the structural strength of the roof?

 

[pattenp]

It's a tension support to help prevent the end walls from spreading apart or bowing. The collar ties and ceiling joist provide the same support in the opposite direction.

 

[oxmanwi]

The reason I ask is I'd like to get a maxjack in the future. But the problem is I have a 8'6" ceiling. I'm hoping to do a tray ceiling of some sorts for the extra clearance. If I made two cross supports on either end from this picture would that work ok you think?

 

[JoeFin]

You might be better off trying to turn them into a Scissor Truss

 

[Zeke]

Your problem is not with the 2 x 4 arrangement but the 2x 6's that support the posts. Since it's a hip with a partial ridge, that's the only support for the middle of the roof. You will need to beef up the joists/collar ties at each end of the ridge before you can remove the structure below. You essentially will be boxing out the supports.

 

[bczygan]

Any time you remove structural members (And all the pieces here are structural), you must transfer the loads they supported, through other members around the space, and to ground.
Where exactly will the lift go, and what volume of space will it need with the largest vehicle and highest height?

There are things that can be done.

 

[oxmanwi]

It will go where the green car is on post #3. My garage ceiling height is 8'6", so with a Maxjack or even a scissor lift I'd need at least 10' height to clear my Ford Thunderbird and Ford Edge. What if I ran two 2x6's to both ends?

 

[bczygan]

What is the roof slope?

 

[Chris705]

oxmanwi - all the horizontal members (ceiling joists and pieced together 2x4 spaning the width of your garage) are resisiting outward thrust from the four roof slopes wanting to flatten out. I believe the vertical members in post #1 are to prevent the ceiling joists from sagging. I understand you want to get to a clear height of 10' so how in post #7 where you add the two 2x6's do you get to a clear height of 10'? You would still want to remove a couple of the ceiling joists would you not? Or at least between the newly added 2x6s? I think the outward forces can be transfered and you have your model to build upon....take a look at what I added to your sketch.....you would remove two ceiling joists, double or tripple up the 2x6s to frame the new ceiling opening and transfer the horizontal load to the new framing....you can do this by using 3/4" plywood above the joists and nailing it off to the shortened ceiling joists and new opening framing.

http://[URL=http://s1283.photobucket.com/user/chris705/media/Fullpagephoto_zpsd44b0664.jpg.html] [/URL]

 

[Falcon67]

I doubt that is structural at all. That and the verticals look more like a "strong back" and some 2x4s to support the ridge beam before the rafters and roof was laid down. It's not doing anything for the end walls or the ridge. The ridge and rafters should be self supporting IMHO. The rafters look plenty big for the span, maybe 2x8 from the pic. There are lots of hips in our house with a 2x8 rafter span way bigger than your shop and no such arrangement in that attic.

Also I think you are mis-figuring the height requirements. My Falcon is 60" at the center of the roof. On a MaxJax the roof would be 8.2' off the ground at the top lift of 48". The Mustang is about 50" and would clear the 8' ceiling.

I don't see any T-bird needing 10' overhead unless you have a real full height lift.

Also, as Chris705 pointed out - if you need clearance in the middle of a bay, you could consider a extra large "attic stair" opening. Meaning, it's a big hole framed like you would for any ceiling penetration that cuts across joists.

 

[Chris705]

Just to respond to Falcon67 post.....in this roof framing case the ridge is not a structural ridge at all and therefore all the load goes to the walls and the ridge acts as a hinge point and wants to go flat or down....when 2-3 feet of snow gets added the rafters there is a whole lot of force trying to push all the walls out because of the four sloped sides of the hip roof. SO all out force is held in check by the ceiling joists and this pieced together 2x4. When we take these out its best to alter the force in some other way and I would be comfortable with what I showed in my description and sketch....just removing them isn't going to work in a snowy 40lbs per sq. foot snow loading situation which I imagine Wisconsin might have. If the ridge was structural then the rafters would only act in a vertical action.... minus any wind loading.

 

[bczygan]

To respond to various above posts, every member there is structural. The loads placed on any particular member vary in direction and magnitude. Any member that is removed, needs to have it's loads transferred to either new members, or an existing member that has been beefed up to take the additional load, unless that member is already adequate to carry the additional load.

This post should be in all caps, but I will assume the OP can read, understand and follow it without the emphasis.

The ridge board/beam is a 2x, rather than a 1x, so it does act as a beam more than a board, for the short span there. And the vertical 2x4's transfer a portion of the roof load to the strongback, which in turn, transfers the load to the ceiling joists. In addition, the collar ties contribute to resisting the tendency of the rafters to spread.

In comparison to many garages that I have seen (Including many hip roofed ones), this garage has the requisite number and spacing and size of ceiling joist needed.

The strongback shown is, I suspect, NOT made up of a bunch of small pieces as shown by the red lines in the photo, but rather, made of two or three longer pieces. The OP can verify with additional photos from the other side. This strongback does a few things that are important. In addition to transferring some of the roof load to the ceiling joists, it also helps with resisting side forces on the ceiling joists and tying the end walls together as mentioned above. It is a key element in the structure.

The drawing above, by Chris705, goes a long way toward addressing how to modify the existing structure to accommodate this lift. One thing that isn't shown is what happens over the lifted portion of the ceiling. Where the two existing joists are cut out, they could be replaced, but 1 1/2 feet higher, and secured to the rafters, to tie them together.

Another thing to check is the roof slope, to see if there is adequate headroom at the hip end, for this tray ceiling.

 

[TommyK]

I doubt that is structural at all. That and the verticals look more like a "strong back" and some 2x4s to support the ridge beam before the rafters and roof was laid down. It's not doing anything for the end walls or the ridge. The ridge and rafters should be self supporting IMHO. The rafters look plenty big for the span, maybe 2x8 from the pic. There are lots of hips in our house with a 2x8 rafter span way bigger than your shop and no such arrangement in that attic.

Also I think you are mis-figuring the height requirements. My Falcon is 60" at the center of the roof. On a MaxJax the roof would be 8.2' off the ground at the top lift of 48". The Mustang is about 50" and would clear the 8' ceiling.

I don't see any T-bird needing 10' overhead unless you have a real full height lift.

Also, as Chris705 pointed out - if you need clearance in the middle of a bay, you could consider a extra large "attic stair" opening. Meaning, it's a big hole framed like you would for any ceiling penetration that cuts across joists.

I agree with Chris it is a strongback. I have installed many. It is only there to keep the ceiling joists from twisting or bowing because the spacing of the joists makes other forms of blocking/bracing impractical. It does not add anything significant structurally. The strength of the roof comes from the opposing force of the rafters on the ridge board (which is not a structural ridge) and the ceiling joists which keep the walls from spreading. The uprights going to ridge are an attempt to stiffen the ceiling not support the roof. You could use cables or threaded rod to replace the ceiling joists with no ill effect if they were properly sized, spaced and attached. No strongback or uprights needed.

A structural ridge would be a member sized to carry the inherent downforce of the roof and would be mechanically attached to the rafters. The stiffness of the ridge beam and the mechanical attachment replace the ceiling joists and serve to keep the walls from spreading.