how heavy is a green roof?
 

Sitting in the hillbilly hot tub this evening (heated with WVO) I was working out the loadings for the roof for the house abuilding. Normally in this neck o the woods they figure 50lbs/sqft, for snow loading. So if I take the 50lbs plus the roof structure plus 12" of wet dirt, I think I may be looking at upwards of 200lbs/sq ft. Any thoughts?

Before you go any further with the idea of having a green roof I think that it would good to know that area that you are in and what the current construction of your roof is.

What are your goals for a green roof?

It depends on what style of living roof you want to go for, the old way was to put down a layer of gravel for drainage then just plane dirt on top of that creating a very heavy layer of soil, but if you use some of the plastic egg crate type stuff that they use for drainage along brick walls you can skip the layer of gravel and if you mix some foam packing peanuts perlite or straw, anything that gives a little bit of air space in the soil and mix in a bunch of compost or the additive that you can put in potting soil to help the soil hold water will prevent you from having to have as deep of soil, compost is ideal as it will add nutrients as well, but anything that will hold moisture will help, from what I've seen, if you fallow these ideas you should be able to bring that foot of soil down to 3-4 inches.

Thanks for the answers, my thinking is that the next owner of the house (I'm a geezer & dont have that much more time to spend on this cool green sphere) may go nuts and add a bunch of weight. So I best be very conservative, since stone is about 150lbs/cuft, I was using that as a baseline. Will probably put a concrete roof on rigid foam. I have a year to work it out.
Tony

I think, it also depends what kind of plants you would like to have, drought tolerant ground cover types would require different soils than vegetables would (I recently came across an article about producing rooftop vegetables, but can't for the life of me remember where!)