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Without seeing your project but trying to relate what you’ve written to “similar” projects I have done, I would say that you can take back your existing roof to a point where your hip rafters extend from ridge to soffit. Then simply construct a new rafter system where you need to. I do not believe you will need much of a ridge beam. A 1×8 should suffice. This is assuming that it is not a cathedral ceiling. and you should step up your rafters to 2×6’s instead of the existing 2×4’s. The rafters combined with the ceiling joists that they tie in next to form a system that typically maintains itself. The ridge does not actually bear much weight at all in this instance, it is the rafter ends on either side of the ridge board and lined up together that place pressure toward each other that support your load and which are in turn kept from spreading out by the ceiling joists tying them together.
Hope this helps,
Pete Draganic
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I have not yet spoke to a P.E., but I thought perhaps one of you had done this before.
We are going to be converting one side of our 1 1/2 story hip roof house to a gable end. When we add on this gable end will butt into the side of a 2 story addition. I am planning a load bearing ridge beam that will eventually be supported on one end by the new building wall. I will not be changing the loading dramatically, but the load path significantly. I have two questions:
1 - Is a load bearing ridge beam needed? The existing roof is straight and the walls are plumb, so it has been OK for 130 years despite five layers of roofing. In doing so, I would be taking the load carried by the fourth panel on the hip and transferring it to the back halves of the two adjacent panels.
2 - Assuming the ridge beam is necessary, can the 4 hip rafters carry the new load at the point of the hip? The way I see it, the same load is currently placed evenly on two hip rafters, so I would be reducing the load on those two by fifty percent, then adding 12.5 (1/4 of 50%) percent back to each of the four. The other 50% of the new load will go to the new wall.
The existing framing is 2x4. The hip is 20 feet square. The roof is a 4/12 pitch. I realize no one can say for sure without seeing; I am looking to see if there is a "typical" way this is done, or if it is possible in some cases to do with out adding a load path from the peak of the hip to the foundation.
-Rob
*Typically in California, when a roof is framed, either conventionally or with trusses, with two intersecting gables, the 'through' part of the roof is sheathed and the connection of the other roof to this is framed on top of the sheathing, creating the valleys. This is known locally as 'California fill'. No ridge beam is used. It seems to me that this is exactly what you are are attempting to do on your hip, so I would think that you could frame the fill right down on the existing roof without any special considerations. You should remove enough of the existing sheathing to provide access to this new part of the attic. I vaguely remember having done this once.
*I thought your description intended the attic to be open under the new gable roof? Which means removing all of one side of the hip roof. I'm assuming you will be removing all the rafters on that side and installing new rafters between the new ridge beam and the existing hip rafters. I still think your plan is basically sound because you're removing load from the existing walls and adding a new column (in effect) in the new addition.
*Without seeing your project but trying to relate what you've written to "similar" projects I have done, I would say that you can take back your existing roof to a point where your hip rafters extend from ridge to soffit. Then simply construct a new rafter system where you need to. I do not believe you will need much of a ridge beam. A 1x8 should suffice. This is assuming that it is not a cathedral ceiling. and you should step up your rafters to 2x6's instead of the existing 2x4's. The rafters combined with the ceiling joists that they tie in next to form a system that typically maintains itself. The ridge does not actually bear much weight at all in this instance, it is the rafter ends on either side of the ridge board and lined up together that place pressure toward each other that support your load and which are in turn kept from spreading out by the ceiling joists tying them together.Hope this helps,Pete Draganic
*Yes, I did intend for this space to be open, with a large doorway into the new construction. Thanks for the good news! I was having nightmares about undoing remodel work to get a load path in at the ridge. I actually was planning on using 2x5's. That is the lumber (from a local mill) will be 1 1/2 wide x 4 1/2 tall. This way the new studs will flush out with the tops of the 1" planks on the old deck. Then I sheet the whole thing. Thanks again, now to see what the P.E. says, and have a joist hanger fabbed for the ridge connection.-Rob