I'm planning on building a garage/shed/barn type building and thought I'd put a green roof on it. I have a proper engineering degree and have read quite a bit about green roofs. But I'm not sure how to approach getting this approved by the building inspector. Do I have to figure out who will be doing the inspection and talk to him before sending plans? Should I just make detailed plans and send them in with the permit application? Anyone have experience getting a residential green roof approved?
Well first, I'm not a huge fan of "Living" or "Grow" roofs. Don't get me wrong, I think they are beautiful, but the lifespan of most is under 30 years the way I see them done. I would strongly recommend doubling up on everything, and also create an air space with small spacer purlins. Also possibly a "cold roof" system as well. With this arrangement, (more $$) you could expect the same lifespan as a good standing seam or slate roof.
Now for the inspector, it may seem a bit clandestine or surreptitious, but a grow roof from an engineering or architectural/design perspect isn't a grow roof, it's a rubberised multilayer roof very similar to (if not exactly like) whats on most commercial buildings with flat roofs. You are just upgrading materials, beam and purlin systems and possible (recommended) venting system, such as the cold roof. I would not even approach that you may (or may not) put a few plants up there, it's not germane to the design or engineering since you have already done those numbers yourself. All they need to know, and understand is you have built an extremely well engineer and strong low pitched roof, that could take way more load than other roofs for you given region. Don't ask questions you really don't need answers to.