Howdy Everyone,

So here's the simple question preamble. I've seen several references to dragon beams and dragon-and-cross assemblies now, but they've all been cases in which the rafter is coming into the assembly at a 45 degree angle; essentially, the building is square and the 4 corner hip rafters meet in the roof center. This makes it easy to create the cross at 45 degrees to the plate and tie, and the dragon at 90 degrees to the cross, putting the hip in the same plane as the dragon.

I, feeling the need to make my project as difficult as possible, want to use dragon beams on a square frame whose hip rafters don't meet at the peak, which means that the bottom end of those rafters will come into the corners at something other than 45 degrees.

Which brings me to the quandry I'm currently in; I'm left with 3 options for constructing the dragon-and-cross. 1) Does one leave the cross at 45 degrees to the plate /tie and the dragon at 90 degrees to the cross, such that the hip rafter and dragon are in different planes? 2) Or does one adjust the angle of the dragon to match the angle of the hip rafter (so that the dragon and rafter are in the same plane) while leaving the cross at 45 to the plate/tie? 3) Or does one adjust the dragon to match the angle of the hip rafter while also adjusting the cross so that the dragon-and-cross are at right angles, but the cross is not at 45 to the plate/tie?

If you could follow all that crap, you're a genius. Here's pictures to illustrate (all images are looking straight down on top of the joint):[img]http://www.flickr.com/photos/rannymo/12453124443/[/img] [img]http://www.flickr.com/photos/rannymo/12452971785/[/img] [img]http://www.flickr.com/photos/rannymo/12453124723/[/img]


Thanks for any input,
Randy

I'm going to be interested in hearing the answer to this one.

Jim Rogers

I would definitely go #3. Two could work, but I don't think it looks as good. I would move the dragon a little farther away from the corner too. Also, if those are really the proportions of your rafter to plate, you can probably skip the whole dragon assembly. As in, that hip is really small relative to the plate width, so there must not be much load on it, and you wouldn't take much meat out of the plate. What's the plan view angle of the hip (the deck angle, aka DD)?

Hi Randy,

Good for you...make it complicated and you will have lots of fun! Then in the end...it won't seem as complicated (at least to you.)

Do not lose sight of "good design," and "elegance" in your design. Following along and then seeing the pictures, the only suggestions I could make at this time is...

1. Look to all vernacular styles (or related traditional systems) you can find. (Swiss, Asian predominantly)

2. Move your cross beam further away from the corner, and/or make two of them. One close to the corner, and one further away.

3. Consider an upright strut supporting the midspan of the hip rafter and resting the base of the strut into the the Dragon itself (perhaps with a through tenon and wedge.)

Good luck, and keep us all up to date.

Regards,

j

That's called a dragon post, I think.

Jim Rogers

As timberwrestler says, #3 is best IMO. That way the hip is normal to the dragon beam, and dragon beam is normal to the dragon tie (cross?) and since the tie already had angle cuts on it in the 45 degree situation it's "just" a matter of changing those angles.

Thanks for the feedback, guys. I'm relieved that everyone's answer wasn't "why would anyone do that in the first place?"

I'm glad to see that option 3 is the favorite so far. That's the way that I originally designed the joint after Jim advised that a dragon-and-cross might be appropriate for a tall-ish hip roof. It seemed intuitively correct that keeping the hip, dragon, and cross normal to each other was optimal for what the assembly was designed to do. But realizing that my intuition, where building big things out of wood is concerned, was about as reliable as my intuition concerning other things about which I know squat, I decided it would be a good idea to ask the guys who know (that would be y'all). I'm still interested in hearing as many opinions as there are out there, so keep them coming!

Here's another bit of info that might change some minds about whether to use a dragon beam at all: that 8x4 hip rafter is going to be supported at the top by a hefty ridge beam, which will reduce the thrust at the plate which the Dragon and Cross is designed to mitigate, right?

If the ridge is posted down to the ground, then yes, the thrust should be reduced. If it's just hanging out up there, then no.

Why don't you post a pic of the grand scheme.

Dead on Jim...it is a "Dragon post," as I know it as well, good point to note.

I second posting pic of full plan.

Regards,

j

Concerning the use of a dragon in conjunction with a structural ridge:

As said, the ridge needs direct support, either posted directly to the foundation or posted to the roof cross beam which is in turn supported to the foundation. The use of a ridge necessitates interior supports of some kind.

What kind of overhang are you going for?

This is an oft misunderstood aspect of ridge beam roof. I you have a ridge beam, your rafters are best arranged hung over the ridge and projected OVER the plate, not seated into it.
If your rafters are seated firmly into the plate, there are better approaches to use than a structural ridge (namely purlins located at about the top third point) If you have a ridge beam and seated rafters, you actually introduce competing forces into the roof structure that really complicate the engineering.

If you choose the ridge beam assembly with hung rafters, the dragon doesn't serve any purpose and is unnecessary.

If you choose a standing roof, with seated rafters, the dragon is not strictly necessary either, it is one of many solutions to this part of the frame. It's a good one though, and attractive.

Right now I'm working on a small bit on roof framing. specifically looking at some forms of roof framing outside of the standard American truss and purlin framing conventions.

It is difficult to give any specific recommendations based on what you've given. It would be nice to know the size and proportions of the structure, the framing of the walls, etc.