Builder/architect ridge beam size question?

[maxwedge]

Probably going to need an architect sign off anyway, but it would be nice to know where I stand first. I have a garage roof that I'm trying to get some extra height in for a lift by making a cathedral ceiling...just need an extra 2 feet or so in the center would be good enough, the the more, the better...anyway.

This problem seemed really complex to the kid designing trusses and, sizing LVL's, and such for the local lumber yard, but in my opinion, it shouldn't be that hard for somebody that actually knows what they are doing...maybe I'm wrong.

Anyway, it's a 28x21 garage, so there is a 28 foot ridge length, 4/12 pitch roof, stick framed way back when, so there are currently no trusses. The roof has new shingles, so I don't really want to tear everything off and re-frame the roof from scratch. Currently it's framed with 2x6 rafters 24 O.C. with a (ceiling) joist every 4 feet. Midwest (central IL) snow loads. Double garage doors, so there is already room and a footing for a post between them to carry the ridge beam load.
Where this gets a bit different is that, instead of removing all the ceiling joists, there will still be 2 (somewhat huge and over-sized) ceiling joists left in place. These are made up of 2x12 cross ties (joists) that are bolted to either side of tripled 2x6 rafters, 8 feet in from each gable wall, which in my opinion should take a percentage of the load off the ridge beam, and it's definitely helping keep the walls from bowing, kind of like spanning two 8 foot sections and one 12 foot center section... but the truss guy didn't think the cross ties should make any difference in the ridge beam calculations at all? Can anybody shed some light on this, or give me an idea how big this ridge beam will need to be?

I'm assuming steel or large LVL either way, but at a certain price point, building scissor trusses out of the existing rafters, or using scab trusses is going to sound pretty appealing.

 

[500bbc]

For the beam calc call any engineered framing member manufacturer and tell them the span of the ridge, pitch, rafter span, roofing material and the snow load. They will calc the beam for you.
No cross ties needed but make sure to use hurricane ties or = to tie existing ridge to new beam. Shape the top of the beam to sit tight to rafters and old ridge.
The existing foundation must be underpinned with at least a 2'-6" x 2'-6" pad at the post locations.

Oh yeah, the beam will flucking HEAVY. They are dense as hell.

 

[coz]

If you only need height in the center, do a coffered ceiling....be a lot less $$ than what you're talking, and you don't have to do the steps, there's a couple ways to do it.

 

[Yellowboat]

Installing a ridge beam would be much easier then that...

Any beam manufactor can do the calcs for you. This is pretty strait forward.

 

[coz]

Installing a ridge beam would be much easier then that...

Any beam manufactor can do the calcs for you. This is pretty strait forward.

No roof tear off involved with that, with a new ridge you do, along with new trusses and webbing if there's more load to carry.

 

[500bbc]

No roof tear off involved with that, with a new ridge you do, along with new trusses and webbing if there's more load to carry.

No existing trusses, conventional framing. Beam negtes the need for any cross ties.

Setting the beam will be a bitch, unless you have a small forklift available. Beam jacks work too, check the local renatl yard and see if they two with enough reach and capacity.

 

[coz]

No existing trusses, conventional framing. Beam negtes the need for any cross ties.

.

Nail it! :thumbsup

 

[maxwedge]

I know I can get a huge beam that will span without ties, but since the ties are going to be there anyway, I'm thinking I can use a smaller beam and save some $$

 

[maxwedge]

Maybe I'm not communicating this problem right. I've already tried the "Free" truss company/lumber yard engineering route. I'm going to see an real structural engineer/architect today anyway, but in case somebody else would like to take a crack at this. Here it is again.
BTW, I have framed/remodeled a whole lot of stuff and used to do it for a living, so I kinda have some idea what I'm talking about, but the so called truss engineers around here don't seem to understand how a basic triangle holds up the roof in conventional attic framing.

An LVL sized to span the 28FT distance and carry the whole load, without ties, in this case is going to be a 4ply 24" deep LVL beam that costs $1700, or a slightly smaller $2500 steel beam, way out of my budget, either of which would be nearly impossible to install, and neither of which will provide much extra headroom anyway...barely more than moving the joists 1/3 up the rafters which would cost about $100 total and which is permissible by code virtually everywhere, even here. My problem which nobody from the truss/LVL free engineering people seem to be taking into account, is that two of the joists/rafter ties will still be in place in my garage anyway, and they are already very over-sized for the job (I use them for hoisting things)... which should make the required beam size significantly smaller? Both so called "truss engineer" kids actually told me that the joists don't really do anything to hold up the roof? (and I'm supposed to trust these kids to design something?) So, I said "Hey that's great news, I'll just remove all the joists since they don't have a purpose, okay?" So, I asked them why the joist where there if they aren't holding up the roof loads, they both said the same thing..."they are there to hold up the ceiling." I said:"That's great because it's an unfinished garage, so there isn't a ceiling... and speaking of which how much heavy, ceiling, drywall do you really think 21 foot long 2x6's spaced at 48" O.C.are really capable of holding anyway?

The joists are in tension, keeping the walls from spreading, which in turn holds up the roof, just like my two remaining joists will still help do, or can somebody please explain why not? I couldn't get an answer from either of them, other than if that was the case, they didn't know how to enter it in the program.

Leaving those two joists means I'm basically only removing a total of three joists from the entire garage and trying to carry that load with a beam...and two large joists in tension, right?

 

[parker ed]

I think you're over thinking the whole thing, get some 2x6's for collar tie's move them up 3' or 4' and nail them on, their going to do the same thing as the cross tie's are now. In order for the ridge to lower the rafters have to spread and the collar tie's will prevent this from happening. No need for a beam under the existing ridge as it is all supporting it self now. You could do some flat diamond tie's across the corners of the garage wall's to help some also. Is the roof solid or spaced sheathing?

 

[maxwedge]

I think you're over thinking the whole thing, get some 2x6's for collar tie's move them up 3' or 4' and nail them on, their going to do the same thing as the cross tie's are now. In order for the ridge to lower the rafters have to spread and the collar tie's will prevent this from happening. No need for a beam under the existing ridge as it is all supporting it self now. You could do some flat diamond tie's across the corners of the garage wall's to help some also. Is the roof solid or spaced sheathing?

The roof is 1/2" plywood sheathing with asphalt shingles on top. It's a 4/12 pitch roof, so moving the ties 4' would be at the roof peak, and I can pretty well guarantee the 2x6 rafters are going to bend and allow the walls to move long before I reach before that point. Even if I moved them 1/2way up and gain a center height of 2feet, it would be enough, but that still needs a stamp $$ because it's past the 1/3 point.

 

[parker ed]

Went back and reread you're first post, wasn't thinking about the short span and pitch. What about replacing the two bolt together tie's you want to leave with actual beams that you could brace the ridge from and run some mid span purlin bracing off of. Im here in Cali. near the beach so we dont have to deal with snow loads.

 

[maxwedge]

Went back and reread you're first post, wasn't thinking about the short span and pitch. What about replacing the two bolt together tie's you want to leave with actual beams that you could brace the ridge from and run some mid span purlin bracing off of. Im here in Cali. near the beach so we dont have to deal with snow loads.

That's essentially, exactly what I wanted to do, originally, but I was told by two different places locally that there's no way to calculate that load, which I know is total bullshit, because timber framing places do it all the time.

Maybe I need to contact somebody that does timber framing or log cabins. The architect I talked with today said he would charge a minimum of $600 just to look at what I had, and probably another $1500 to draw something up. I told him no thanks. It's also occurred to me that I could conceivably jack the whole thing up and build a short knee wall under it for less than $1500.

 

[whiteworks]

essentially you are going to remove the 4 center cieling joists. I would start by oversizing your 2 existing 2X12x21' josts to 4x12x21' and also doubleing up your 8 remaing 2x6 joists. I would also place 4x4 coulmns under those new 4x12's. I would then temp up the ridge and remove the 4 center joists. Next run two 4x12x10' from the new 2x12's approximately 6'6" in from your exterior walls by using bigass simpson hangers. I would then frame a pony wall on top of that up to the existing rafters and place a color tie as low as possible. this will leave you with an 8'x10' opening that could be at least 2' higher than your current ceiling. Lots of simpson harware and you should be good to go.

 

[Old Texan]

If seeking a professional to look it over, get away from the architects and find a structural engineer. I sell overhead cranes systems and cringe when I have to deal with an architect. You should be able to find an engineer by referal that will do it on the side and a whole lot cheaper than an architect.