I have framed many gable roofs with the cieling joists raised off the plates to create a vaulted cieling. I have always used a rule of thumb of no more than 1/3 the height from the plate to the ridge and usually err on the side of caution.
Well this time around i goofed and found myself with a situation that due to a tall window on the gable end I have to be more than the 1/3. My height from plate to top of ridge is 74″, the bottom of the ceiling joists are 29″ from the plate. That is more like 40% rather than 33%.
7″ pitch, 20′ wide room (10′ rafter span), 24′ long. This situation exists for 16′ of the length of the room. The remaining 8′ the ceiling joists are still off the plates but are lowered to 9′, well within the 1/3. I always bolt the ceiling joists to the rafters.
I was looking for some opinions. Is there anything that I can do to ensure that I have a well framed roof system here.
I can (but don’t want to) still get a structural ridge in under the existing ridge board but it won’t be fun.
Replies
I don't have an answer, but here's a sketch of your questionView Image
is there an over hang raftertail, plumb soffit, or no overhang?
is there a ridge board or a sructrual ridge beam?
Are you just starting to frame this or are all the rafters up?
Are the walls framed typoically with a double top plate and joints somewhere along the way?
There are several options here, depending on your answers
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10" ovdrhang
rafters are up
2x8 rafters 2x10 ridge board
double plate with joints
Can you sister another 2 x 8 rafter at this point? Might be the easiest way to add strength.
PS - I am not an engineer.
Bryan"Objects in mirror appear closer than they are."
Klakamp Construction, Findlay, Ohio
Tghis is one of those - you really need an engineer for this - things
But the problem is that you are trying to counteract the outward thrust being placed on tyhe walls from the load on the rafters. One typical way is a structural ridge and the other is a rafter tie placed in the lower third.
This project is small enough, and the ties close enough to right, that I am tempted not to worry about it except for a couiple things.
One - I don't know what your snow/live load requirement is.
Two - It is going to be awfully hard to fit proper insulatuion into that 7.25"" rafter space and avoid ice damns in the north - unless you plan to spray foam in.
So to resist that outward thrust on the walls from the roof raters, you need a flat beam in opposition to that thrust. better to have a vertical beam handling the load directly, but you can resist the horizontal thrust by mmaking your soffit a box beam laid down, or by using an LVL sub offit and perpendicular to the wall. This would get more expensive IMO, than inserting a structural beam.
All thqat said, it seems that the capacit5y of the existing rafter ties should be considered as worth something. The problem there is that the roof rafters, being only 2x8 are going to be stressed inthe lower third. This probably would have all worked as is with 2x12 rafters and 2x10 ties well bolted, but now yiou needt o work backwards - one thing an engineer canassits with is not only reviewing options, but costs too.
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This is coastal CT. The snow load is 30lbs.
My gut tells me that it will probably be OK but I am going to seek some advice. I know a structural engineer who looks at residential as residential and not like ievery project is the Hoover Dam.
In regards to the insulation, when I have designs with short sloped areas such as this I trade off using 2x10 rafters with having to fur them down to get the right depth. It helps to use a smaller rafter when I am trying to match up fasia and soffit heights. I also enjoy saving my back from havinfg to haul up the larger rafters. A little time spent ripping some material down to 2" and fastening them doesn't seam too bad to me. The reduced height at the wall ceiling location is hardly noticable.
Hi,
I take it that this high window has a header in it. How wide is the window and how big is the header. You might consider dropping the ceiling joist down on the header, just above the window and inch or two. Then you could take some angle iron, bolt through the joist and bolt or lag through the header. That would drop the vault some and if you attact the joists to the header all should be well. larry haun
Have to talk to the local truss-meister, but it seems a scissor-truss arrangement might work for you.
(How do you post a picture in the text? I always have to attach a file.)
Jon