Nail withdrawal capacity for wind uplift
Nail withdrawal capacity for wind uplift
(OP)
Is this allowed under the IBC? There is an(2005)NDS table that shows nail withdrawal values. I remember under the old UBC, it's not allowed to rely on the withdrawal of the nails for support.






RE: Nail withdrawal capacity for wind uplift
Garth Dreger PE
AZ Phoenix area
RE: Nail withdrawal capacity for wind uplift
RE: Nail withdrawal capacity for wind uplift
RE: Nail withdrawal capacity for wind uplift
Typically and what I have done in the past, the supporting legs would be installed directly on top and along the existing joist or truss lines for support.
The manufacturer provided sealed calcs stamped by a Civil PE showing their justification. The way they did it is that each leg reaction (gravity or uplift) approximates a man weight (200-250 lbs), which I get. The part I'm skeptical with is the use or reliance in the existing plywood nailing into the existing joists/trusses to keep the system in place.
So let's say the legs of the panels are screwed into the existing plywood sheathing, between the joists/trusses. The plywood is supposed to span between the 2 joists/trusses to support the legs then the plywood nailing transfers the uplift force into the joists/trusses.
This is for a location with no snow load consideration. I'd like to hear what you guys think of the mfr. claim?
RE: Nail withdrawal capacity for wind uplift
Garth Dreger PE
AZ Phoenix area
RE: Nail withdrawal capacity for wind uplift
RE: Nail withdrawal capacity for wind uplift
BA
RE: Nail withdrawal capacity for wind uplift
RE: Nail withdrawal capacity for wind uplift
Garth Dreger PE
AZ Phoenix area
RE: Nail withdrawal capacity for wind uplift
When you attach something to the sheathing, between trusses or other structural support, the sheathing then has to transmit the load to the structure through...nails.
I would not allow any equipment subject to wind uplift or overturning to be attached to only the sheathing. Two problems exist...one is the fastener pullout of the fasteners attaching the device to the sheathing. The second is the secondary effect of the additional load on the sheathing fasteners. Attach such devices only at the support and make sure the fasteners have length and capacity sufficient to handle the pullout from the support level.
RE: Nail withdrawal capacity for wind uplift
So just what kind of uplift is there from the solor panel?
Garth Dreger PE
AZ Phoenix area
RE: Nail withdrawal capacity for wind uplift
RE: Nail withdrawal capacity for wind uplift
RE: Nail withdrawal capacity for wind uplift
RE: Nail withdrawal capacity for wind uplift
"screw" anchors into plywood and rely on the withdrawal values of "nails" at the framing members below into which the plywood is anchored. My response to that would be yes, if the screws used have sufficient achorage values into the plywood to resist uplift at the PV system anchorage points. You are not changing the overall uplift pressure on the roof by adding PV panels -- you are only changing the distribution of the loads from uniform wind uplift to concentrated point loads at the standoff leg anchor points. By the time the uplift force at the standoff anchor points is distributed through the plywood sheathing into the trusses and/or framing members below via nails, the nails can't tell if the forces are coming from concentrated standoff point loads or uniform wind uplift.
RE: Nail withdrawal capacity for wind uplift
The change is most likely cladding-related, rather than MWFRS, but needs to be considered for both.
RE: Nail withdrawal capacity for wind uplift
between the plywood and the truss/joist members to provide the uplift resistance (assuming a complete load path). I wanted to bounce it off to other engineers to get a feel if some of you guys share my concern. Thanks again.
RE: Nail withdrawal capacity for wind uplift