Expert: Dan Griffin - 10/31/2009

Question
Location: Southeast - FL
Roof Type: 1960 home
          Gable Roof,
          Howe Girder Truss (2x4)  (nailed metal gusset plates
          2.5"/12" pitch  
          built up Bitumen w/ small stone finish (2006-surfaced)
          1x8 tongue & groove sheathing

house is rectangular shape 55' long by 25' wide

trusses span 25' - strapped w/ plaster board for interior finish

i have a mid structure section of roof (15') in length where the trusses are same pitch on face, but peak 1' short, and descend to posterior of house (same angle) ending approx 5' short of remainder of homes trusses.  it was where a car port was closed in.  all are preformed trusses

I have set up a new load bearing wall to be consistent with remainder of homes posterior wall

i want to scab onto lower chord of the (7 in total) short trusses to extend to same length as others.  they will rest on new load bearing wall.  I was going to overlap by 3' and use 3/8" hardware to join.  then extend upper chord on (front side) up 1' in similar fashion to peak at same hieght as remainder of homes trusses.  then send a (new) upper chord on posterior of home to meet the extended lower chord.  finally replicate Howe Girder Cross webbing that is consistant with remainder of home trusses.  

Is this feasable???
Have you seen this done??

I have far to much plumbing and wires to attempt to slide a preformed half truss in place to make this extension.  

Answer
CJ, if I am following what you are proposing, it sounds like the original truss is remaining the same and you are adding some heighth at the ridge and one top chord.  If your new bearing wall is designed properly, it should be able to carry the original truss and whatever new ceiling joists/rafters that you are extending out over the car port.

The very best advice would be to have a truss manufacturer agree or suggest how to add the extension to the old top chord.  This would involve a detailed dimension drawing of what is there now and what changes you are proposing.  You need this drawing for any approach you take for knowing lengths of material,etc.  I think I envision the carport rafters as totally independent of the trusses other than you are attaching to them for rigidity and to get in plane.  They may well be able to make up the extension as a unit that fastens to your existing truss which will make the "open time" quicker.

I would avoid cutting into the existing truss if it can be avoided.