Hi all, looking for some help with a porch roof detail. I`m adding a 3:12 shed roof off of a 12:12 main roof. The porch roof will cover a porch area of 9’spanx20’wide (screened in eventually) and needs 3′ of overhang to cover the log work below. I was planning 2×10 @ 24″ o.c. with 19/32 CDX on top (tile). Would the Simpson skewable brackets work ok at the top and do I need a birdmouth at the plate or can I go straight across the supporting log with a flat cut on the log top that matches the roof pitch. If I go with the flat cut I wouldn`t weaken the 2×10 rafter and could use L-50 brackets but I`m concerned about thrust loads. At the top, should I use a piece laid flat under the top of the rafters to better distribute the load and support the ends from bowing the plywood if they don`t fall on an underlying main roof rafter? The main roof is also 24″ o.c. w/ 19/32 CDX.
Clear as mud? Thanks for any input.
Replies
Mosseater: This is how I resolved a 10/12 and 3/12 porch Valley intersection with a Log Wall. The Valley was actually 7"×12" rather than 6"×12" as labelled in the graphics. The common rafters were 7" deep, spaced at 33" on centers and since the joinery was visible the commons were to intersect the Valley at reasonable close to the same height from the bottom shoulder (I came close - about 7/16").
Due to the large difference in pitches the Valley was shifted sideways one foot to increase the overhang on the 10/12 bumpout (initially only 7.2" compared to 24" for the 3/12 slope ... not very pretty). The wall was kerfed (visible in one of the photos) and the Valley was mortised in the log wall as well.
The upper surface of the log beam was cut at a 3/12 slope and this meant two options at the intersection with the Valley rafter. One solution was to cut a variable seat cut in the Valley rafter. The sketches and calcs relate to the other option. Since there was lots of meat on the log beam (15" diameter) and a post only a foot away we cut a slot in the beam to accomodate the Valley.
The sad part about this is that I usually don't travel to the final assembly site and I can't really answer your question regarding connectors. However, in the past we have used Timberlinx, through bolts (sometimes with knife plates) or 1/4" to 3/8" metal gussets in conjunction with lags.
Not exactly the same as your situation but maybe it will give you some ideas ... ? :)
Edited 9/26/2006 2:35 pm ET by JoeBartok
Edited 9/26/2006 2:44 pm ET by JoeBartok
Edited 9/26/2006 2:47 pm ET by JoeBartok
Edited 9/26/2006 2:48 pm ET by JoeBartok
Forgot to mention: not only was the beam slotted at the Valley intersection but the ridge on the 10/12 bumpout received the same treatment. The Valley trough on the upper surface of the roof was the datum line; there was no way the bumpout ridge log and kerf on the wall were going to be moved. Initially I was told the 7" deep commons were to simply rest on top of the ridge but before I got into the calculations too deep it became apparent that this wasn't going to happen. So the ridge (16" diameter minus material removed to cut slopes - lots of wood) was slotted to permit the commons to sit at the correct height.
Our rule of thumb is never to remove more than 1/4 of the beam depth.Joe Bartok
Thanks for the reply. Although interresting, not really what I had in mind. Nice place! I see what you mean about the backing angle. I had to do one on my dormer and it worked out great. I use the calcs from an ILBA news letter and nailed it. Except for the shrinkage! Taking that wide a cut from a not so dry log, well you know the rest. Thank God for trim, it opened up an extra 1/2" on the main roof side. Lesson learned.
Any trouble with differential shrinkage on the porch roof ridge? I see the nice little truss in the middle or did you do some hidden magic there? Maybe not enough involved logs to matter much, eh?
I see the short purlin pieces up there, stick dormers? Those look like some Western logs. Ain`t bent up enough to be from around here. What species?
If I can figure out how to post a pic on here I`ll show you what I`m doing.
Try this. The picture of the back with the temp tin is the roof I`m working on.
As of now it's only been about a year and a half since the logs have been cut. They are Eastern White Pine and for sure there's going to be shrinkage. The screw jacks under all the posts in the structure should take care of that problem.
Looks like I'm not going to be much help. I haven't travelled to help erect a building in years and have no idea what connectors were used in this particular house. Even if I did know it likely wouldn't help you out any. Each roof we do is different and the hardware is engineered.Joe Bartok