Existing scissor trusses adding a ridge beam

[DonEee]

Looking for some thoughts on existing scissor trusses in residential home. Built in the 60’s or 70’s I have someone with scissor trusses in their living room/kitchen area. The clear span of the scissor trusses is roughly 32’ @ 24” o.c. They are fastened to the top of the exterior walls. Currently, one bearing wall is experiencing a small amount lateral movement (bowing), from the deflection of the scissor trusses. The opposite bearing wall isn’t showing signs of lateral movement, probably because the garage is attached to it, perpendicularly. A solution that has been thought of is to add a ridge beam at the centerline of the trusses, which will help to reduce the outward thrust of the exterior walls from the deflection of the trusses. Is there another solution that I am not thinking of that can help to eliminate the bearing walls from bowing? I am trying to evaluate the most cost effective solutions.

 

[jayrod12]

Well it's likely that now that they've moved, they're pretty much set in place. If there are some return walls you could look at turning the soffit into a plywood beam that spans between the return walls. I've used this idea successfully a few times.

 

[CANPRO]

You could use an occasional tension tie (round bar, threaded end, turnbuckle) anchored to the top plate of each wall. Might be cheaper and less intrusive than a full length ridge beam.

 

[Ron247]

Is the problem cosmetic or do you think the scissor truss has a structural integrity issue? Laying a multi-ply LVL beam flat near the eave could be a possible solution. Biggest problem with it is space to work near the eave and what pitch is may be laying on. The width of the room is a factor regardless of a ridge or eave solution.

 

[DonEee]

I thought about tension ties. It doesn’t really work because they would be located at 7’-0” above the floor because of the height of the end walls. However, it’s above code requirements for head clearance.

I don’t think there is structural integrity issues with the trusses. They might be slightly under engineered for today’s standards. Long term outward thrust on the exterior walls is my main concern. Uplift is also a concern I had, a ridge beam would solve this. Another concern is if the homeowner adds a second layer of shingles to the roof in the future.

The only cosmetic issues right now is the drywall on the interior side of the bearing wall. Exterior brick and mortar joints are in tack.

 

[Agent666]

If its just visual and not getting worst I wonder if there is a way to reset the perimeter wall to being vertical/plumb by lifting trusses off the wall and either straightening the wall or rebuilding it and setting the same trusses down again. Seems about the same amount of work as putting in ridge beam, plus ridge beam only addresses further movement and doesn't fix the current movement observed.

Internally you could just strap and line the wall and add more drywall so visually it's plumb but behind the scenes it's still leaning over, just hiding it if you like (provided the trusses work struturally still).

 

[BridgeSmith]

If CANPRO's tension ties were attached to the truss a foot or 2 above the wall (giving it 8 or 9 ft of vertical clearance), would that be an option? You'd have to check the shear capacity of the truss members around the attachment point, and maybe reinforce it at those locations.

 

[DonEee]

The more head height with the tension ties might work. Although it will require more of the existing ceiling to be torn up to access the trusses for reinforcement.

Some other details I failed to mention is that there is a level below, a basement. The floor joists for this kitchen/living area sit on a bearing wall with a footing that aligns with the centerline of the trusses. Adding a ridge beam should not require new footings for any columns, pending load calcs and evaluating the existing footing.