Multi-ply Sill Plate/6x6 on Top of Tie Beam

[kmart30]

Contractor needs to put a new roof/trusses on an existing CMU structure with a continuous reinforced tie beam at top of the bearing walls. He wants to raise the new ceiling/roof about 6" above the existing tie beam. He doesn't want to add an additional course of block but he mentioned installing (4) 2x sill plates or (1) 6x6 and anchor bolting to the top of the existing tie beam to make up the height difference. Besides making sure multiple plies get nailed and spliced correctly does anyone see anything wrong with this? I know its outside conventional practices but I couldn't find anything in the code that doesn't allow it.

 

[KootK]

I can't think of a reason to veto this. I'd give some thought to how out of plane wall loads will make their way from the top of the tie beam up to the bottom of roof trusses. There's some meaningful eccentricity there and you'll not want rely on bending perpendicular to grain in the sill assembly. Especially so when it would be bending perpendicular too ply interfaces.

 

[skeletron]

How was the original roof constructed? More labour involved with the sill plates. When will they call for anchor bolt inspection? After the first plate, or the last one? Which is better for inspection purposes? Bearing values for 2x versus 6x6 should tied to the species. Maybe better quality wood with 6x6. What is the availability of the wood pieces? What is the contractor's preference? Less shrinkage with the 6x6 potentially.

 

[kmart30]

Original Conventional framed roof damaged beyond repair so it is a complete tear off and they are going back with trusses. Contractor wants to avoid adding extra course of block because its a different sub then the framer who will more than likely install the plates and bolts. All thread rod drilled & epoxied thru plates/6x6 into the existing tie beam to resist out of plane shear and uplift. Species will both be SYP No. 2 pressure treated.

I am leaning towards the 6x6 due to ease of construction, less shrinkage, and less fasteners. Anchor on each side of splice with a horiz. flat strap across the splices? Similar to what the code calls for when you have a single top plate at the splice...

 

[KootK]

All thread rod drilled & epoxied thru plates/6x6 into the existing tie beam to resist out of plane shear and uplift.

A fair bit of bending on the bolts, no?

Anchor on each side of splice with a horiz. flat strap across the splices?

Does the tie beam not function as the chord/strut? I would normally expect so and, in that case, there would be no requirement for sill splicing.

 

[jayrod12]

Wait, if you're going with trusses, why can they not just build the different bearing elevations directly into the trusses? I get them to do this all the time. They can provide you the extra 4.5" (or whatever is required) moment connected to the trusses with their plates and you just have the contractor either leave the original sill plate in place, or install a new single/double as required.