Thanks, What I'm reading agrees with your recommendation for the insulation. I am starting to learn the pros and cons of the various waterproofing systems for a flat roof and so far, am leaning toward the pvc, but welcome any info on all. The roof we have in mind will include some variety of coverings, including mostly low growing ground cover, some large potted shrubs and pavers for a patio area.

PVC, TPO and EPDM are all single ply systems (1 layer). All of the laps are either heat welded or glued. If installed by a qualified professional these system will not only last their manufacturers warranties but are cost effective. Torch on is at the very least 2 layers you can make it 3 but the costs are higher. Generally speaking a 2 ply torch roof will cost 15-20% more than a single ply. The inflated cost is well worth it. Again you must make sure this system is installed by a qualified professional (journeyman roofer). With a torch on roof you rely on flame torches to weld the laps together literally melting the seams and laps together. You must make sure your roof contractor is heavily insured with this system and I recommend asking for a certificate of insurance stating their liability limits and that their policy states the use of a commercial flame clause. This system is the best regarding a flat roof application. As you probably already well know from your research flat roofs are very different from sloped. Sloped just shed water whereas flat in some cases are designed to almost hold it with a very slow runoff. Think of them as somewhat of a pool although ideally you still want to shed the very slow runoff.

Thankyou, plan on using this on my boathouse, still don't understand how they didn't have to have railing though

I have been reading that the various components (drains, insulation, growing material, etc.) of the green roof can double the life of the water proof material. Can anyone shed a little light from personal experience? The green roof would add a lot of expense to roof replacement, but would become cost effective with an increased roof life span.

The cost of installing a green roof is pretty pricey in itself let alone replacing one. You are right though the life span of the waterproofing system is significantly increased. The reasons for this is simply UV or should I say lack there of. The reason why manufacturers place a warranty on their products is for worst case scenarios. The waterproofing membranes are designed to withstand the elements and the worst element by far over rain and snow is UV. UV breaks down the membrane over time ultimately becoming a water problem, hence warranty. With a green roof system it is considered an inverted roof and the waterproofing membrane never sees the light of day. Therefore increasing the life span quite considerably.

We're joining the conversation late, however, I'd encourage anyone to look into LiveRoof systems. We are the LiveRoof grower for the Rocky Mountain region and love and stand by our product. The lifespan of roofing systems is increased up to 40 years with our product. Let me know if you have any other questions about green roofs!