Truss blocks above porch overhang 2

[met33]

I have a couple of questions about truss blocks (aka drag blocks or shear blocks). This is my first time doing them, and they are uncommon in my area. The blocks will go between roof trusses above the exterior wall of a single-family home, adjacent to a porch overhang.

1) Is it advisable to order the truss blocks slightly undersized (e.g., 1/8" less wide and 1/4" less tall) than the nominal dimensions of the opening in which they will be installed? To prevent the roof truss spacing from "growing" horizontally due to tolerance stacking, and to ensure that the roof sheathing can lay flat above them, in case the adjacent trusses are slightly shorter than their nominal dimensions.

2) Does anyone have experience with alternate connection methods, other than A34 or A35 framing angles, which I assume are most common? I'm considering SDWS framing screws in a face screwed or toenail configuration for connecting the truss block verticals to the adjacent roof truss webs, and SDWC truss screws for connecting the bottom horizontal of the blocks to the wall top plates.

Below is an example of a truss and its corresponding truss block. Some other areas of the roof near hips have shorter blocks.

Below is a relevant detail from Mitek:

 

[RontheRedneck]

They're called "blocking panels" here. But names for most construction-related things varies a lot by region. There is not technically correct name that I know of.

You mentioned possibly making them undersized. I strongly recommend that. The lumber in the trusses isn't perfectly straight. And you have to account for the plated. I'd suggest making them 1' 10 3/8".

I also like to hold the verticals in 1/2" if the EOR will allow it. More clearance for crooked lumber and such.

The things are expensive. Both to buy and to install. So if you can get by with one every other truss or something like that, it will save the customer a lot of money.

If you can make X-bracing work that's better still.

BTW - Don't assume there will automatically be a vertical above the bearing. There's no practical reason for it. If you want one there, I'd suggest specifying it.


Also - If I were designing the above truss in your example I would "idiot proof" it. i.e make it symmetrical so it can't get set backwards.

When framers set trusses, they're not thinking about engineering. They're thinking about how much the crane is costing them, how tired they are, getting off early enough to get to their kids' soccer game, etc. Setting trusses backwards is a constant problem we deal with.

 

[met33]

Thank you for confirming that undersizing them is preferred for installation purposes.

Great idea to make them symmetric to prevent installation errors! I'll do that. The truss plates on the bottom two corners are currently larger than the top two corners, so the upper two plates will need to be enlarged.

Yes, the installation will be expensive, especially with A34 or A35 framing angles (so many fasteners to install...). That's why I'm looking at using a combination of SDWS framing and SDWC truss screws as an alternative. Total hardware cost will be similar, but installation should be faster.

Most of the truss verticals line up over this wall, I assume the truss designer did that on purpose. A couple of them are off though and need to be moved.