Sorry I may not have explained it well. I will throw in another picture for clarification.

Yes the roof has rafter ties but no truss system other than the rafter ties. There is no king post or web. Just a top chord a bottom chord and a splice.

The splice is over the "load bearing wall," whether or not it is truly and really a load bearing wall is of little consequence since when I pull the wall out from under the splice I am likely to get sag unless I reinforce it some way. I just am trying to anticipate costs. I am assuming that I will have to put a sunken beam in but am wondering about other options.

Really since two new walls are going up I am hoping to add a new splice in ceiling and double up the 2 x 10's in the basement and let it roll. I am not optimistic that I will be so lucky.

The existing wall carries the dead load of the ceiling joists and the ceiling itself. If the attic is accessible and storage is possible I would also assume a live load of 20 PSF.

All that would be required is a header below the ceiling joists. If you want the ceiling to be unbroken the header can be raised but some method of connecting the ceiling joist ties is needed so they can continue to act as rafter ties.

If the new walls carry the load to a foundation you could sister new ceiling joists between them.

Thank you.

I understand that it is a load bearing wall. I doubt very seriously I would ever revert to attic storage. The attic is adequate for it, but my plan is to just add insulation over the joists and be warmer in my house and the house has plenty of other storage options. But it never hurts to be prepared.

My question really is do you think an overhead beam will be adequate or do you think I need to go through the trouble of sinking the beam. I know both options will require joist hangers.

I threw in a picture close to what I was thinking (mine would not have studs or drywall of course).

You actually have 4 header options, 2 of which will be more costly than the 3rd or 4th, albeit, more aesthetically appealing.

Thw least desirable;

A strong-back is a header placed above the ceiling joists and supported at it's ends by a continuos post or blocking and the joists carried by 2x or 4x12 hangers. This will also affect the rafter ties, depending upon their height above the ceiling joists.

A flush header where the joists are supported by 2x hangers, which also, because of the placement of the rafter ties may affect them.

A partially dropped header which is placed tight beneath the rafter ties and the joist are carried with 2x hangers, but breaks the ceiling plane.

The simplest and least destructive;

A full dropped header where the wall is removed and the header is placed tight under the bottom of the joists.

Do you really want to double-up your floor joist, if you do not have too?

The ceiling/attic joists appear to be acting as the rafter ties in a conventionally framed gable roof with unheated attic system.

The only problem with the drawing is that side mounting of the hangers means the top of the new beam will need to be braced laterally to prevent rotation or the hangers need to be centered in the middle of a two piece beam.

I would design the beam and hangers for a moderate storage load. To get more than 2 nails into the upper half of the hangers you might need one for two 2x14's or a Simpson HUS 212-2 (see link).

Here is a link that might be useful: Simpson HUS 212-2