What Happens When… There is a Knot in a Truss Web Member?

Posted by in What happens when ...?, Wood | May 07, 2018

Here we have a truss web member that is fully fractured.  Close examination of the fracture discloses a knot that extends from the top face down to the bottom face, nearly the full width of the member (Figure 1).  The knot is so big in this member that it should have been discarded during fabrication, but apparently somebody was not paying attention.

Large knot extends full depth top to bottom and nearly full width

Figure 1 Large knot extends full depth top to bottom and nearly full width.

Such a large knot renders the 2×4 extremely weak in bending side to side.  The pattern of the fracture indicates that it probably occurred when someone pulled the 2×4 sideways for balance or lifting oneself into the attic.

I know by experience. I had one like this in my own attic.  It fractured when I pulled on it to lift myself into the attic.  It did not take much sideways pull to fracture it.  I repaired it by clamping it on either side and bolting the new sister members to the existing web.  By the way, I still use it to lift myself into the attic.  It is stronger than ever.

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