Following is the text of a message that I just e-mailed to an engineer, that was listed on the TFG resource guide, regarding a problem I am having on a house that I just finished framing. I am much interested in, and would much appreciate others' input as well. (Also, what is the best way to make the pic viewable to those on this forum. It was downloaded into Irfanview, and is now a JPeg.)
Thanks, Alvin Gregorio:
I got your name from the resource guide on the TFG site. I have a little something I was wondering if you would want to take a look at. I am a framing-contractor, working in Bakersfield, Ca., at the south end of the San Jauquin Valley (seismic zone 4).I do a lot of my own designing, and redesigning of plans that I work on.
I am involved in a house project that I redesigned the central great room (single story, it's a rectangle in the center of a rectangle, which is the house, patio, garage)from traditional (non-timber frame) scissor-trusses, to a vaulted, exposed-beam roof/ceiling type design, per the homeowner's wish to make it feel as "mission" style as I could, while still controlling the budget. As you can see in the attached photo, the house is already framed, using a kind of a hybrid framing system going on for the roof/ceiling.
Although we had the plan and design "engineered", our engineer is really unfamiliar with this type of construction, and we feel that he missed the boat.
I drew a up a design, using 4x8 RRs, @ 5' oc with a structural ridge beam covered with SIPs. The overall span is 22', and the length, or run, is 35'. The pitch is 3/12. The top of the shed roofs that butt the great room's outer walls are at +12'. The eave plate height at the great room is 15' .
Our engineer did away with the SIPs (to control costs), and did away with the structural ridge-beam, probably again to control costs. It would have been huge; we are using concrete tile with mortared ridges and hips. He designed DF 4x12s @ 64"oc with DF 2x8 purlins in hangers @ 16'oc (the 2x8 was so we could get enough insulation in), which leaves 4" exposed after drywall.
When I saw his design, I immediately questioned the builder as to what was going to control outward thrust. The exterior, eave walls are made up of 2x4, with 3 clerestory windows on each side. Even if the 3' of wall from top of shed roofs, to top of Great Room walls were able to control outward thrust (which we discovered they weren't, even though I took the liberty of doubling up the 2x4 studs and king-studs), and not bend at the top of the shed roofs, I had little confidence that the lower roofs and perpendicular walls, spaced as they were for rooms and patio, could control the outward thrust put on the Great Room eave walls with an eventual dead-load of about 40psf.
Contrary to what you see in the attached photo, our engineer's original design did not have any collar ties. This was exactly my recommendation when I first saw his plan. But again, the builder assured me that the engineer had a handle on it. Just as I was finishing building the roof , I noticed that there some serious outward thrust going on--this is without concrete roof-tile. So back to the "engineer" we went. And his response was, "I was wondering about that".
We installed 4x6 ceiling/collar-ties, bottom @15'. Because the rafters were already run, the collar ties are cut to 21'-5", and slope cut to fit tight under the 4x12 RRs. The collar-ties do not bear on anything (not that I think that they need to). The connection between the collar tie and the RR is an 18 Ga. Simpson Strap x 22" long., filled with 16d sinkers, one strap on each side at each end (totaling 4 straps per)
Now here's my question, should this hold? Is this a good, or adequate design. Keeping aesthetics and budget in mind, how would you design it. I'm not against taking a lot of it apart, in order to get it right.
If this is something you would like to take on, please let me know how much your end would cost.
You can contact me via my e-mail, or my telephone number is 661-827-9200, or 805-828-5128--cell.
Alvin Gregorio--Design & Construction