We are putting a new PVC membrane over a 400 sq. ft. flat roof. I am concerned about the contractor nails and screws going through the roof deck (3/4 inch wood slats) and damaging recessed lights and electric wires within the roof (about 8 inches deep). Just below the roof deck are about 13 recessed lights and flexible wires gong to them and fiberglass insulation. The space between the roof deck and recessed light cans are 3/4-1 inche.

How does the roofer avoid hitting these things? (a) Do they just carefully select screw sizes to not extend more than 1/2 inch under the deck? Or do they locate and mark the areas on the roof above the cans so workers can avoid screws in those areas? (and how do they do this?)

To complicate matters, they are using tapered insulation (from 2 inches to 1/2 inch). Is it possible to carefully select and use different screw sizes on different sections of the roof? For example with 2 inch insulation, use a 3-1/4 inch scew (2 for insulation + 3/4 for deck + 1/2 inch under the deck). Where the insulation is only 1-inch, us a 2-1/4 inch screw. etc. Is this too much to ask a roofer to do?