Roof-ponding-deflection-limit, in roof systems that are essentially flat, provisions must be made to support ponding water. ponding is a progressive event. the more water on the roof, the more deflection you get, which means that even more water can be retained, which leads to more deflection, etc.... I would say the rafter and purlins are undersized for dead load deflection and the roof has a flat zone, the hail wouldn't have helped. i would do a model and check you deflection ratio's i think for 1 deg you should be aiming for l/500 or something like that., i know the deflection limits for each member are l/360, 240, 180...for each member. but if the rafter deflects 2 at midspan and purlin deflects 1.5 at midspan..
Design solutions for building code-permitted low-slope applications that cause ponding water. by scott d. coffman, p.e., secb, and thomas g. williamson, p.e. chapter 15 in the 2015/2018 international building code (ibc) contains installation guidelines that permit a design slope of 1/4 in 12 for certain types of roof covers. specifically, the code text typically reads, …, 154 paper the emergency discharge is always thought to be installed at the edge of the roof. it is assumed that a stable equilibrium state exists with a water level d above the support as shown in the left part of figure 2..
120 it can be derived  that z = a/π, so that the bending moment in the middle is: m va z qˆ 2 2 0 π a = ⋅ = (8) this bending moment m0 corresponds very well with the bending moment as a result of a uniformly distributed load q, since: 7.752 8 4 ˆ 2 2 2 2 2 2 0 a a qa qa m ⋅q= ≈ π π π (9) the first-order deflection in the middle of the beam δˆ0 can be determined by considering, building offsets are common and create intersecting planes that contribute to drainage issues for low-slope applications. design professionals frequently specify the minimum code-permitted slope with little, if any, consideration of the resultant valley slope created by the intersecting planes (figure 1).ponding water is commonly observed at valley intersections for low-slope roof and deck ....
The lower end of the deflection curve is also a typical location for ponding, water stains, and damaged framing members (figure 5).this opinion is based on observations made during forensic investigations., 4 4. example of a steel deck and insulated single-ply roof. 5. secondary structural member deflection limits at a 25-foot span. conventional steel framed buildings. Composite stage deflection. the composite stage is when the concrete has cured and the deck is acting as tensile reinforcement. deflections at this stage are calculated using elastic analysis, neglecting effects of shrinkage and by using the average cracked and uncracked second moment of area of the slab.