Post Installing Roof Diaphragm Blocking

[jlleiber]

I have a contractor that has installed the roof and shingles on a 5 story apartment. However, they forgot to install the diaphragm blocking. Obviously, it's costly to rip the shingles off to be able to get the appropriate nailing through the sheathing into blocking below. Are there any methods of attaching the sheathing to the blocking from the underside?

 

[sandman21]

Honestly, I would make them install per plan, but you might be able to use an A35.

 

[KootK]

You could screw blocking into the deck from the underside. My main concern would be compromizing the roofing above with the screws. How far off are you on shear capacity with an unblocked diaphragm?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jlleiber]

sandman - that's what I'm thinking. I do like the A35 clip idea as a potential though. I'll explore that further.

KootK - the contractor submitted a request to nail through the underside, which is no good. I agree that screwing through the roofing puts the roof above in jeopardy.

There may be a compromise in terms of finding how much of the roof can go without blocking and the rest of it needs the roof torn up and adequately blocked

 

[MotorCity]

What if you don't attach the blocking to the sheathing? The load would still find its way into the blocking via the truss chord. This condition is similar to providing blocking that is not full height which I have seen done many times at the eaves because of the need for ventilation.

 

[KootK]

What if you don't attach the blocking to the sheathing? The load would still find its way into the blocking via the truss chord.

I believe that, without attaching to the sheathing:

1) You haven't increased the number of fasteners transferring shear from one panel to the next and;
2) You haven't braced the panel edges against shear buckling.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[msquared48]

Apply the blocking flat, nailed (with 6d nails) and glued to the plywood or OSB sheathing, and toenail the ends to the truss top chord.

Not the best option, but better than nothing.

Mike McCann, PE, SE (WA)

 

[MotorCity]

Maybe ignore the diaphragm all together and add a few more members to create a truss in the plane of the roof?

 

[Tmoose]

How thick, and what material is the roof sheathing?

 

[DaveAtkins]

I would do everything possible to make the diaphragm work unblocked. For example, if wind controls, can you reduce the Exposure Category?

If there is still a problem, I think I would try to get comfortable with gluing the blocking--no screws or nails! I would be afraid that in the process of "trying to get your numbers to work out" you end up creating a bigger problem--a leaky roof.

DaveAtkins

 

[jlleiber]

The material is 19/32" Plywood.

I like the idea of flat blocking, but like Dave said, a leaky roof using nailing/screws is a bigger concern.

And I'd rather not reduce the design of the building to meet the as-built condition.