I was poking around in my garage this weekend and noticed that the bottom cords of my trusses have sagged 1/2″ lower than the gable trusses(measured mid-span). Is this normal? I haven’t stored anything up there in the 19 years I’ve lived here. Don’t know about the previous owner. All of them appear to have sagged the same amount.
Trusses span 32′, 3:12 pitch, 3/8″ sheathing with 3 tab shingles. Cords are all 2×4.
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I wouldn't have expected a half inch, but some deflection is normal. Any building material will have some "give" in it. The chords of the truss are in either tension or compression, and will compress or stretch a bit with those loads. So some deflection is normal.
In your case, the low slope probably contributed to it. A higher slope wouldn't have quite as much force in the chords, and wouldn't deflect quite as much. Lower slopes have more force in the chords.
With a low slope, every milimeter the chords compress or stretch is amplified, and results in proportianately higher deflection. With a high slope, the compression or stretching doesn't result in as much deflection. (Not a perfect description, but the best I could off the top of my head)
But basically I'm saying I wouldn't lose any sleep about it.
The beginning of wisdom is silence.