Truss loading and deflection math.

You need to determine the max height of the wall - in all probability the truss
is designed for deflection of l/360 - take the span in inches and divide by 360 -this
gives you the lay down of the truss under dead load - then add to that the live load
factor - and finally creep - and your there.

For a truss with a 26' span that would be (26*12)/360 = .87" - then for a 10psf DL and
a 40psf LL - (50/40)* .87 = 1.09 - and finally the creep - creep is 1/2 of the total
deflection allow by dead loads - so that's .87/2 =.44".

So total max deflection would be .87 + 1.09 + .44 = 2.4".

But - now comes the fun part - in a new house - from the point where you begin to live
in it - it should already have reached it's dead load lay down which leaves you 1.53" for
live loads and creep. And in a house 20 years old you have proably reach your creep load
which would leave just the 1.09 AND - to top it all off - you said that you increased the
load by roughly another 2.5 psf by adding a layer of sheet rock - and plan to add another
load to it with plywood and drywall.