Existing Wood Truss Analysis

[SoFloJoe]

Hi All,

I have an residential home that was built in 1968 in South Florida. There are 31ft long trusses with 2x4 at 24" o/c (see truss layout attached). There currently are 2 interior walls that the owner wants to remove from underneath, they have horizontal bracing which initially led me to believe they are load bearing. BUT after further investigation there are no connection points, one has an air gap of about 1/2" and the other is snug to furring strips (not a real structural connection). Both of these are within 10ft from the wall supports.

I used 64psf (conservative, probably can bring down to 55psf or so) load per today's criteria. I found the top and bottom chords are failing. I found the capacity to be at 29psf, assuming 1000psi DF wood. Today we normally spec Southern Pine but who knows what they used in 1968? (An actual question and figure of speech).

Could have +/-30psf been a standard load for HVHZ in the 60s/70s? I am not sure if I am being overly cautious here. Ideally we would not have to do anything and can remove the walls. But if not, then my solution would be to either add beam/support to replace 1 or 2 of the walls OR stiffen the affected trusses with additional 2x4s. I hesitate to stiffen the trusses only b/c then I now own the truss if there are any future issues with it, you all concur?

BTW, there is a jog in the structure just beyond these 3-4 trusses where the span drops from 31ft to about 25ft with trusses running the entire length with no supports.

Thanks in advance for any input!

 

[Ron247]

The pictures look like #2 SYP to me. That looks like really good #2 SYP. I was a carpenter in the 70s in the southeast and most lumber was #2 SYP except wall studs. Walls studs were S-P-F.

 

[1503-44]

We used 1500 psi for southern pine in early 70's truss work. Looks like some pretty good wood there.

 

[SoFloJoe]

As long as it's not the one with an air gap. That could do more harm than good.

No, not that one. But it is the one that is snug, it has no structural connection though. The furring strips are tight against this wall.

Should there be some sort of strapping/connection to the trusses bottom chord? I hesitate to connect them so the existing condition can remain. But they probably should be fastened?

 

[jayrod12]

I wouldn't change a thing about it. Leave it in place as is. The more you touch it, the potentially worse off you might find yourself.

 

[SoFloJoe]

Thanks jayrod12.. that was my thought too