RJ Elder Design There is a waterproofing membrane installed over treated wood 1x2 sleeper strips that are nailed to marine grade plywood decking which spans over your joists system. The sleeper strips are what your finish tongue & groove decking will be fastened to. The waterproofing membrane should be self healing so that the penetrations from deck screws will not create leaks. It should be run under the sleepers as well and roofing tar should be applied to all screw penetrations and seams. In the end, there should be a watertight air cavity underneath your finish decking and in between your sleepers that allows any water to flow to the outer edge of the balcony instead of leaking through the porch ceiling below. Also, the balcony should have metal flashing at all edges that fits under the lip of the waterproofing membrane. The deck should have a slope of 1/8" per foot as well to help water drain. The sleepers should be run parallel with this slope to allow the water to move.

Your level of comfort on the second floor balcony should not be impeded at all since you will be able to use the deck without fear of puncturing the waterproofing. This type of installation is quite involved and really takes a competent carpenter to ensure that it is installed properly. It is also very hard to describe without proper section drawings to help explain.

I hope I've answered your question.

Barn Light Electric Company Those look like the Round Nautical Marine Bulkhead Light. They measure 7 1/2 inches in diameter. Here's a link to the listing for more information: http://www.barnlightelectric.com/discount-lighting/marine-lighting-docks-decks/round-nautical-marine-bulkhead-light.html

Hope that helps!