Replacing a non-structural ridge board with a structural ridge beam

[Bill McNiel]

Jeff,
First off, I am a Registered Architect (Architects are required to be "registered" along with nurses and sex offenders) and have designed and built a number of remodels with similar structural/aesthetic parameters to those you have presented. So.....

No apparent need to install a new ridge beam with the addition of the "collar ties" assuming you are creating a new framing system, think connections, that acts somewhat as a truss. What you need to do is introduce some horizontal members at the wall plate line to counteract the natural resolution of the downward forces from forcing the walls outward (these element will be in tension so they can even be cables) or prove that the existing roof framing is rigid and strong enough to resist the outward horizontal pressures . This outward force is currently being resolved by the ceiling joists tying the two walls together.

I would advise you to retain the services of a Structural Engineer for calculations regarding force resolution and connection details. You are on the right path.

[Jim Becker]

Bill brings up something that resonates...you may be able to modify your setup to provide a lot of extra headroom, but you may still need to retain a few horizontal members to insure the building doesn't bow out at the top of the walls from the weight and pressures exerted by the roof system. The great room in our home is a good example of this. While the ceiling is "cathedral", there are two large barn beams that hold the wall structure securely vertical. Beams or heavy cables may be required for your particular structure to be able to open things up without risking structural integrity.

[Greg Cuetara]

Jeff not sure where you are located in Maine but PM me if you are interested in finding a Structural Engineer to help you out.

Greg

[Jeff Keith]

Thanks everyone for the great responses - very helpful. I anticipate getting a structural engineer involved once I get all my ducks in a row. I just want to have a few different options sketched out beforehand that are structurally sound at least in principle.

Cable ties or tie rods are the most attractive options at this point. They can provide the necessary lateral support while opening the space above, and they look cool. I'll need the help of an engineer to figure out all the anchoring variables, etc. But, I may end up doing what Jim Andrew suggests just to give me a bit more head room. Anyway, I'm so glad I asked this question here.

Greg, I'll send you a PM shortly.

Edit: I should add that one of my concerns is not so much the dead load (the roof itself) but the live load, namely, the snow we get here in Maine.

[Tom M King]

All such calculations are done per a sq. ft. load for a particular area, which takes into account snow load, as well as wind and other factors. Span tables are for different loads per sq. ft. Here in North Carolina, design load is 20 pounds a sq. ft., but I always overbuild anyway and use 40. I expect up there it would be double what it is here, but that's just a guess. It would be easy to find though, and even your building inspector can tell you. Since the building is only twenty feet long, a strong ridge can easily take care of the spreading load with good connections of the rafters to the walls.

Over the years, I've built stuff that needed an engineers stamp. I always approached it like: Here's what I'd like to do., rather than: What do I do?

[Steve Peterson]

It sounds like the new properly supported ridge beam is going to handle the complete roof load once it is installed. Is the purpose of the short cross members to support the roof while the beam is installed? If that is the case, then it would be much easier to use 3 or 4 temporary vertical posts. The ridge beam should be able to be placed under the existing 1x8 with short horizontal cross members supporting the bottom of the beam. The roof (and the new ridge beam) needs to be designed to support your snow load in Maine, possibly around 40lb per sq ft. However, you should be doing the work in the summer when there is no risk of snow. The temporary vertical posts will have very little load.

Steve

[Jim Riseborough]

Yes, get a structural engineer, up in Maine, I imagine you get alot of snow.

If you choose to put the new beam down lower, You could create a saddle across the rafters for the new beam to support on, just a 2x12 cut and screwed and glued so you could get a joist hanger onto the side of the new beam. Sort of creating a deeper section at the end of the rafter so you can get good load transfer.

I could do a sketch if that would help.

[Ted Calver]

I don't think the proposed collar ties will do much for you in resisting spreading. Their primary purpose is to keep the roof from opening up at the ridge in high wind load conditions. Sometimes they are replaced by metal strapping over the ridge connecting opposing rafters.

[Jeff Keith]

Thanks, again, everyone for your comments.

Ted, I agree that collar ties alone are not sufficient for lateral forces, but my original plan was to use them in conjunction with a structural ridge beam. I've moved away from that plan. I now need to consult an engineer and approach it as Tom suggests:

"Over the years, I've built stuff that needed an engineers stamp. I always approached it like: Here's what I'd like to do., rather than: What do I do?"