Washer head structural screws on skirts and girts: Sink the heads flush?

[rbstern]

Is it acceptable to flush-sink the heads of a washer head structural screw for skirts, girts and plates on a pole barn? I was thinking, for those exterior surfaces, I would use 16D galvanized, ring shank nails, with perhaps a couple of flush sunk deck screws added for additional pullout resistance, to avoid the protruding head of a structural screw. But then I saw a video where a builder was sinking structural screws to be flush with the girt/skirt surface. Seems like that would hurt the pull-through performance of the structural screw. Another approach would be to shallow counter-bore the holes for the structral screws to avoid crushing the wood.

Am I overthinking this?

Input appreciated.

 

[WranglerX]

Considering the the resiliency of a wood structure, I think you are over thinking it.... Only real danger may be at end of board/timber and causing it to split...

 

[Rustyiron]

I sink them flush and switched from the GRK RSS to Simpson. Bigger and flatter head.

 

[herm0016]

run them flush and call it a day. overthinking it.

I have always used the fasten master ones and they have been great. I am sure simpson and GRK are good as well.

 

[rbstern]

Flush it is. Thanks.

 

[s219]

I use GRK screws extensively for pole buildings. For the RSS (washer) heads, I just drive them until the washer is flush, not the entire head. To make the full head flush you'd be driving them in quite a bit and crushing the grain, which is not the point if that style. If you need the screw head to be flush, get the GRK R4 head screws, which have cutters on the under side of the bugle-style head so the wood won't split. They work well.

For #10 and below, GRK makes RSS and R4 in most sizes and lengths. It's only when you get to 1/4" and larger that only RSS is available.

I rarely use screws for wall girts since vinyl-coated ring shank nails from an air gun have such good holding power (try to take one out, it's a chore). But I often use the GRK screws for roof purlins because it's easier and more surgical working with screw gun up on the roof, and depending on the wind load, I might want the extra pullout resistance for uplift. Two #10 R4 screws in each purlin/rafter connection gives a lot of pullout resistance.

 

[rScotty]

I use the GRK for work where I think appearance is important. I sure do like the torx head drives and the wide washer head.

And recently for a pole shed I have been using the Simpson large washer head. They are great where strength is what I am after. I use two portable drills, always pre-drill to the minor diameter or a bit over, and generally let the head just lightly crush the wood ..... maybe for about 1/3 to 1/2 of the washer head thickness. I keep a block of wax nearby & sometimes lightly wax the screw.... it depends on the wood.

My goal is to balance the required compression of a strong joint with the natural elasticity of the wood.
So just how tight to sink the head varies. For soft pine I might sink the washer half way or more. For oak or ash, hardly at all.

RB, ....No, I don't think you are overthinking it at all. The fact that you ask the question says a lot about what kind of builder you will be.
rScotty

 

[rbstern]

Appreciate all of the replies. Thought I'd add another question here, since I have the attention of experienced builders.

Is there a practical consideration for number of girts? The plan I am working from doesn't have details for girts. I've looked at a lot of images of unskinned pole barns, and see a lot of different choices. I plan on using a 2x6 PT skirt. The side outside plates are 2x8 (inside as well) for rafter support. I figured I would put a pair of 2x6 girts between, but I have an opportunity to do it less expensively if I use 2x8s for the middle girt(s). Any reason I can't get away with a single 2x8 girt between the skirt and the plate? I don't have to worry about metal fastening issues, since the sideing will be vertical pine board and batten, of a thickness of my choosing.

 

[Rustyiron]

I think some of your terminology is different from mine. If I understand you, your "plate" is basically a tall wall girt or purl in and you'll have 2, one outside and the other inside. This is in effect the beam for the trusses. These sound small, are you using some type of "kit"?
As for the wall girts/purlins, I'd use something between 24"-32". Basically a length in that area that gives you a even nailing pattern for the siding. (Divide the wall height by X to get it in that 24-32" range. These are important beyond just holding the siding on and actually helping to "rack" the building and attach an actual diagonal brace to.
You need to visually separate all the other Lumber in these pictures, but look for the diagonals. VERY important to have at both sides of every corner if possible.

What's your post spacing and how long are the trusses?

 

[rbstern]

This is the plan: http://web.utk.edu/~ggrandle/Programs/Plans/T4161.pdf

Only mod from that plan is we are building 36x36, instead of 36x48.

I'm using their terminology. "Plate" is how they describe the split member rafter support beams on the plan.