Expert: Dan Griffin - 1/11/2008

Question
I want to remove a load bearing wall and want to convert the roof into a truss system.  The new room would be 25' wide by approx 18' long.  The wall being removed is perpundicular to the ceiling joists and is 15 feet long.  

I want to make sure putting a center 2x6 from main 2x6 running length of house(centered) 2/4'sa at 3' from center diagonal and at the 6 foot marks(perp).  I will place on 20 joists continuing past supported ceiling.  

Will this support this ceiling?

Answer
Karl,
I think I am following what you mean.
YOu want to remove a load bearing wall.
You want to create a truss by adding a 2x6 on top of the joists and using 2x4's as webbing up to the existing ridge beam.
The room is 25x18 and your removing a 15'wall - I assume you are removing 18 feet of bearing.
Is there not roof bracing pushing on this wall's top plate?
There is absolutely no storage or decking in this attic space?

I have never used a ridge to carry a ceiling load and I question whether it would work, and would be hesitant to recommend it.  The more I think about it, though, the more I think it might work, but I've not seen it and cannot offer encouragement that direction.  The very best suggestion would be to work with a structural engineer and follow their directives.

I am guessing that you want to remove the bearing structure under the 18' dimension.  You need to carry the present load with a beam of some sort that has sufficient bearing capacity on each end to carry the load which might require additional studs.  The bearing wall is carrying about 225 SF of the ceiling as a uniformly distributed load.  Assume the ceiling load at 10 lb. per SF dead load to give a 2,225 lb load (some designers use 5 lb dead load and a 10 lb live load which would increase the load).  Each beam end is carrying 1,112 lb. and the load is about 124 lbs per lineal foot on the beam.  My table for headers not supporting floors or roofs says that (2) 2x12 can span up to 16 feet carrying 150 lbs per lineal foot, you are over this span number by 2 feet.  I have built trusses in the attic space to remove bearing walls, but the trusses have always been independent of the roof structure with the top chords meeting and working with a king post similar to these: <http://www.public.iastate.edu/~mwps_dis/mwps_web/tr_plans.html>.

I would not be comfortable designing the truss points or gussets to accomplish this with the ridge.  I would still recommend presenting the issues to a structural engineer.