Any suggestions for the best way to prevent rafters from spreading if the ceiling joists are not running in the same direction as the rafters? We have a house that is 26′ wide and 32′ deep. It will have a 10/12 pitch roof with the 2×10 rafters running front to back (the 32′ direction), but the 2×8 ceiling joists run side to side (the 26′ direction). With this situation, the ceiling joists can’t act as a rafter tie, holding in the bottom of the rafters and keeping them from spreading. There will be 2×6 collar ties at 8′ above the attic floor.
To complicate matters, a master bedroom in the back has a vaulted ceiling (see drawing). This will be 13′ wide and 15′-1″ deep. I may put in exposed rafter ties at every 4′ in this room at ceiling height to try to hold things together.
Thanks for any help.
Brockway
Replies
Here's a section of the roof. Don't know why it didn't show up with my original post.
Brockway
A structural ridge is often used to support roof loads when there are no joists to tie things together.
Al Mollitor, Sharon MA
Merc pretty much said it.
Adding collar ties is a waste of lumber and won't prevent anything from happening. You need either a properly sized ridge beam or you need rafter ties in the LOWER third of your rafter span. 48" OC won't cut it either. Not a whole lot of options here.
You could also try running a search here for this subject. This topic gets debated to death every two months or so.
My first thought is ask the person who designed this what he was thinking, I assume he is the responsible party. When I came across this problem, we were told to run a 2 x 4 strongback on top of the ceiling joists, from front to back, 32 " oc., tied to the rafters. Used a lot of material, but house never moved.
Greg in sleeting Connecticut.
Can you get some down supports under the ridge? That will keep the ridge from dropping and the walls from spreading. You could also double up the collar ties and that will help. Can you get a strong back under the rafters with some bracing back to a wall? Anything to take the load off of the outside walls.
James Hart
At 8' up, those 2x6 collar ties are totally worthless. Why not move them down to immediately above the ceiling joists? You could also use metal tie rods as collar ties, which certainly produces a more "architectural" look. I have this detail on my screen porch roof which has no horizontal wood members. Just a big 12/12 roof. It almost seems to defy gravity. I can try to post some pictures later (machine with the pictures not online now).
If you can't get collar ties, the you will need a structural ridge as others have said.
MERC.
Brockway, I would install "wall ties" every 8' or so. I would make them out of 2x4, standing on edge, lapped and nailed together at the middle. I'd probably order 18'ers to give me a 4' lap. If you don't think every 8' is enough...put more in...put one on every rafter if you are paranoid. Also, these would work fine if you layed them flat.
If you have any interior partitions intersecting your bearing wall, install windbracing on them.
Shoring up the ridge (mentioned earlier) will also help.
Someone mentioned lowering the collar ties, but I wouldn't. The collar ties are there to prevent uplift...not to keep the rafters from spreading.
blue
Warning! Be cautious when taking any framing advice from me. Although I have a lifetime of framing experience, all of it is considered bottom of the barrel by Gabe. I am not to be counted amongst the worst of the worst. If you want real framing information...don't listen to me..just ask Gabe!
Since this hasn't been built yet, you might want to re-think the whole structural design from the top down. You have an interior wall on the top floor that divides it into 15' and 17' rooms. If you use that to break the span of the ceiling joists, you can turn them 90 degrees so they tie the rafters together and span a shorter distance than the original 26'. Of course I can't say for sure that that would be a better decision without knowing a whole lot more about the whole building, like are there interior bearing walls that break up the 26' dimension?
Trusses would be another thing to think about. These would be high enough that the route from the truss plant to the job site would have to be looked at.
-- J.S.
John, the height isn't an issue with truss builders....they just piggy back them.
I once set trussed on a commercial building with some giant sized piggys...they had 40' bottom chords! Incidently, I was the only guy working the top when we set the bottoms. I created three sets of "truss clamps". As soon as the truss landed I would clamp the top in three places and then start nailing in the top lacers. I was staggering 16' linial in a way that allowed me to anchor the new truss, then have time to fall back and fasten all the lentgth behind me. Then, two feet over, I'd get another 16'er ready for the incoming truss. By the time the last truss was set, all the lacing was done behind me!
The key is using those truss clamps.
blueWarning! Be cautious when taking any framing advice from me. Although I have a lifetime of framing experience, all of it is considered bottom of the barrel by Gabe. I am not to be counted amongst the worst of the worst. If you want real framing information...don't listen to me..just ask Gabe!
These being 14 ft. high, it might be possible to do them in one piece. Was Boss Hog around when you used to be here? He's the resident truss designer now.
-- J.S.
Either reverse the ceiling beams and run them with the rafters like it's supposed to be or double up the last ceiling beams like on a hip roof and put outriggers in perpendicular nailed to the double with joist hangers and nailed to the top plate and rafter and then put strongback in.
Joe Carola
Edited 11/11/2004 7:35 pm ET by Framer
50063.9 in reply to 50063.1
Either reverse the ceiling beams and run them with the rafters like it's supposed to be..
"...SUPPOSED TO BE..."?!!!
Joe, there's no such thing as "supposed to be" when it comes to these matters. For instance, on a large hip, there will always be one set of rafters running "the wrong way".
ceiling joist are often dictated by underlying bearing points. Rooflines are dictated by exterior asthetics. Sometimes the two clash, but competent carpenters/builders always have solid solutions!
....and I KNOW you are one of the competent ones!
blueWarning! Be cautious when taking any framing advice from me. Although I have a lifetime of framing experience, all of it is considered bottom of the barrel by Gabe. I am not to be counted amongst the worst of the worst. If you want real framing information...don't listen to me..just ask Gabe!
Blue,
I meant like it's supposed to be because the house is a basic gable except for the master bedroom. Of course on a hip there will be one set of rafters running the wrong way that's why I told him to double up the last two ceiling beams and put outriggers and strongback on like a hip roof.
I've never once framed a simple gable roof like this with the ceiling joist running that way before nor have I ever seen it drawn that way before so for me with a simple gable roof like that in his picture it shows the girder running with the rafters and the floor beams and ceiling beams running perpendicular to the rafters instead of the girder running perpendicular to the rafters and the floor beams and ceiling beams running with the rafters on top of a center partition that sits above the girder. So in my eyes all he needs to do is double up the last ceiling joists and put outriggers in like it was a hip roof with some strong back like I said before.
The architect probably drew it that way because if he put the girder the other way the floor beams and ceiling beams would be spanning 16' instead of 13'. 16' is not a big span to me at all.
Joe Carola
Both problems are solved by use of a structural ridge beam supported to carry roof loads to foundation.
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Question from a novice......... doesn't the 2nd floor subflooring and 2nd floor joists act as a single unit to prevent the outward thrust? There's a FHB issue about retro fitting a dormer ( October/november 2000) The house in that article has floor joist similar to the gentleman with the orginal post??? I didn't read the article in great detail but it didn't seem to have a structural ridge beam.
As a general rule, no. There can be ways to make it so, I suppose, but I am not familiar with that article or job.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
The second floor deck would resist outward thrust if there was any at the floor level. But there isn't. The problem here is the rafters creating outward thrust at the second story ceiling level, pushing the tops of the walls apart. At the bottoms of the walls, there isn't a problem.
-- J.S.
brockway
Presumably the 2x8's are split into 2 spans? If so and it works with the rest of your bearing then instead of ceiling joists why not build a second floor package (2x10's?)and sheath it and then sit your roof framing on the ply? You'll have box beam to hold the walls together and it will make the attic plenty useful down the the road assuming you can get to it somehow. How about a few dormers?
In the master I'd post a structural ridge, like a nice piece of d.fir.
Yes i like spending other people's money.
cheers