Changing crossbeams?

[Makoto]

Hey guys, my garage has 7 or 8 2x10's joists running front to back (each sitting attop the wall studs and connected to the roof) with two pieced together crossbeams on top of those.

The roof is a four sided pyramid with a 25 degree angle.

The 2x10's make the ceiling at 8ft and i'd like to get another six inches (a foot would be great) out of it before I put sheetrock up. Here is an image of the beams.



I'm wondering if I could leave some of the joists and just move over the ones above the garage door so I can raise it a hair then reinforce that area in some other way. It seems like these boards just keep the walls from falling down as well as supporting those 2 top beams.

The roof is brand new so I'm not ripping it off.

Any suggestions that do not involve a complete rebuild of everything from 8 feet up?

 

[Makoto]

here's kind of what i'd like to do. is this possible?

 

[BFBOB]

Looking at the photo and your diagram, I believe your restructured roof would be weaker. The issue is the distance from the rafter to the top plate. In your revision, the resistance to wall spreading is applied above the wall, and will result in a bending force being applied to the rafter. It appears in the photo that the current collar ties are at every other rafter. I would double that, placing your new collar ties at every rafter in the region where you're removing the current ones. I'm not an engineer; that's just what I would do in your situation- and your garage structure looks identical to mine.

Another thought about resisting the bending force on the rafters- you might be better off using nails or screws (without pilot holes) than bolts. The reason is that the holes you must drill to use bolts will cut the longitudinal fibers that give wood its strength; nails and to a lesser extent screws don't; they just push the fibers aside. If you do use bolts, keep them on the center line of the rafter. That's where there is little if any tension or compression to begin with.

Doesn't look like a major problem to me - I'd sure proceed with the project, but again, I'm not an engineer!

 

[Hpozzuoli]

I too will be raising the joists in my dad's garage this summer. My plan is to do one at a time and bolt them. I will also drop some legs back down to the top of the wall on an angle for each one. We have 10'6" of clearance and need to get to 11'6" in order to fit a higher rv. If my dad doesn't get the rv then I don't have to do it.

Unfortunately the door openner needs to be raised and an extra panel added to the door.

 

[Makoto]

I just found that image on a website, I just want to know the best way to keep my garage from falling down if I raise my ceiling

 

[SteveCh]

I helped a buddy do this to make room for a lift. Worked great. I was the guy up high doing the main work, and I did one beam at a time. Been ten years and has held up fine through wind storms and one heavy snowfall [three feet].

It was dusty, hot work, but we did it in about four hours, I think it was.

 

[Makoto]

So here's kind of what I'm thinking of doing. It will only require moving over 2 joists a little and moving the one right in the middle elsewhere (im nore sure if this is enough to compromise the structural rigidity.





What do you guys think?

 

[readhead]

Do you realize that whatever you do you have to do in both directions because it is a hip roof?

 

[Makoto]

I don't know what you just said.

 

[Zeke]

I don't know what you just said.

Basically all four corners are tied with an X brace in most of full hip roof construction. You must have some X and Y bracing there. The important thing is to preserve the bracing of the corners. I see no reason given the limited amount of information that you can't raise one rafter and move 2 others.

 

[readhead]

Just keep in mind that the walls that are parralell to the rafters might be affected by what you are doing. The two ties that are on top of the joists are holding the end walls together.

 

[sands35]

You are basically converting a rafter tie to a collar tie. When that happens the tension load on the beam goes up the higher the beam is mounted. The problem isn't with the beam, but with the attachment points and methods.

You are in Texas, so snow load isn't a problem but wind load is.

To be on the safe side, I would sister a new rafter onto the existing one then double the collar tie, one for each side of the rafter. Use a big bolt to hold up the collar. The problem will be tearing the collar off the rafter under load, not breaking the collar or the bolt.

engineering of the tie:

http://mathscinotes.wordpress.com/2010/11/29/the-mathematics-of-rafter-and-collar-ties/

(But the real answer is call an engineer and pay him/her a few hundred to tell you what to do, not listen to some joker on a message board! )

 

[LX-Markham]

(But the real answer is call an engineer and pay him/her a few hundred to tell you what to do)

ding ding ding

anything is possible to do, just needs to be done right.

 

[Makoto]

I've decided on a plan.

I'm going to double up on all the joists (i noticed cracking in one joist already and another has been repaired for cracking all the way through prior to us purchasing the home) and move the ones which are in the way to the side of my new channel.

So right now it has 6 joists, in the end I hope to have at least 12 joists with a center channel wide enough for whatever is on the lift. I really think that will be sufficient while allowing for some attic space and the lift.

I'm also going to use hurricane straps and 2x4's for reinforcement to the roof to keep it from blowing away even though we are in a wooded area.

Thanks for the input guys