permaculture sod roof

Hallo,

We have a foot-deep sod roof.  The builder loaded it, over 400 square feet, with a heavy clay soil and without any drainage or gravel layers.  We've had problems with drainage.  One half of it gets heavy sun and is quite dry, the other gets more shade and stays wetter.  Right now it grows a mix of a winter rye combined with wild seeds that have blown up on it.  Our climate gives us deep winter freezes, heavy snows, lovely springs and falls and summer heat. 

I would like to improve this soil by mulching it heavily.  It would be a great, deer-free vegetable garden addition.  It's easily accessible from the house and we have a faucet up there to help with watering.  I'm wondering about the behavior of water in great soil on a roof, though.  I know that beautiful soil will hold more water.  The roof is very strong.  Will great soil keep more water in itself and have improved drainage to the outside edge drains, or are we asking for more trouble?  Does anyone out there have experience with a great, relatively deep sod roof?

Warmly,
Lorca
Bozeman, MT

Lorca,
We are also a Montana based home.With a green roof structure.This one however was carefully designed and built to utilize a bit lighter load then what yours has been.
 A previous home passive solar home  my other half designed, built and constructed utilized a top soil depth of 2 feet.However it was removed after a gang of gophers moved in making one heck of a mess through the liner as well as enjoying the the tasty insulation package.
So let me give you a bit of information from my green roof designing and landscaping experience.
  First off I am not sure what your builder was thinking, LOL,, my opinion anyhow.Roof gardens can be very viable living and growing spaces  to utilize. We designed ours to be  another entertainment area of our home as well as beautifully landscaped very detailed out with sedums growing with in design patterns.We also have a stone patio and 2 good sized stone planting areas there as well.
 Do you know what your roof liner is composed of ? If you have a a good epdm liner? Do you know if your home roof system was built with a  pitch for drainage? Living in Bozeman you may have the insulation system built out of Belgrade that comes with a pitch for drainage.Is there drainage in place around the building such as a french drain to direct water away from the homes wall?
Do you have any idea what the bearing load for your roof actually is designed for? If I  just take of from the amount of fill that your builder placed on the roof structure I can offer some suggestions provided he was good about sticking to the design guidelines and did not push the limits..
 If this is what your roofing system is composed of I can offer you some suggestions for you to consider to turn. it into a productive space. This  is going to be work for you if you decide to change it.
 .First off find out if the clay pack is directly over your liner or if they put in some type of barrier to protect it from  stone movement or critters .Many commercial roof gardens are also covered with a drainage type system that is placed under the soils.This is important because you will be removing this  the soil from the home.Adding mulch and trying to improve the soils on the roof will not help with the drainage if your wanting to grow plants that do not thrive in a clay type base.With the amount of clay sitting on this roof  you may wish to fully remove it  and put on something that is more productive plant friendly.You may wish to also add in walking areas.If your weight load allows you may add some hardscape choices as well..Make sure your liner is protected and then you could go about replacing with an equivalent  amount of good grow mix.You can also do this with a sheet type method like lasagna gardening , the Ruth Stout methods, even the straw bale types of gardening allowing for break down over a couple of years with it as a grow medium etc...Personally myself when I design a roof garden I go the lighter custom soil mixes that I blend myself.
There are 3 types of roof garden forms to look  consider intensive, semi intensive and extensive..What you basically have  with a sod roof and are looking to establish is a semi intensive garden.You just need to trade out your growing medium and not just add to it with a weight burden from additions and more water holding capacity which could push it past your weight bearing load.
 Better soil on your roof with a proper drainage is better for the roof structure itself.The  run off into your outer drainage I assume also goes into an area of for productive growth.
The roof on our home is designed with both semi intensive usage available if I so choose to put it into affect,However my personal choice has been to keep it extensive using light growing mediums and very low care plants.
Perhaps this can offer you some thoughts to consider.
Hugs,Laughter,Light,Love
 Mary
Northwest Montana

Found a picture of our roof, for you to look at as well and see some other possibilities..Hopefully I can figure out how to post it..LOL
M&J

HappyHouse wrote:
Found a picture of our roof, for you to look at as well and see some other possibilities..Hopefully I can figure out how to post it..LOL
M&J

That is pretty sweet!!!

Do you have anything growing up there that you can eat? 

My wife and I were originally thinking about going with a larger building, but now we are considering building one of these types of homes.  I should probably order Mike O's book soon.    We may be building it this year.

Kegs,
  We have grown quite a few things up there.We have a couple semi intensive beds on the roof that have a deeper soil medium for deeper rooted plants. In the past we have grown peppers, tomato,spinach,lettuce mixes, mustard,kales, onions, cabbage,cucumbers,strawberry , many types of herbs and flowers matter of fact the kitchen cook herb perennial herb garden is moving that direction this year.Have to remove a bed of mints and lemon balms..Over amongst the stone patio we have some thyme and such for the kitchen use now.For the first couple of years I planted the heavy areas as full as possible using inter planting to get the most food from what we had there.
  When we were able to come up with a workable straw bale garden for over the only flat place here which is our drainfield.We decided to inter change out our veges on the roof garden and went with low maintenance sedum.Our roof is set up for added entertaining.
Neither of us  read Mike's book until about a year or so ago..LOL, We bought a piece of land that was listed as a rv parking area or innovative building.Mostly hillside only one flat area big enough for the drain field.Since we happen to be innovative ,creative and  the property is in a great location( in between our 8 kids).James has designed and built solar passive homes with intensive garden roof structures before.So we come into this with previous experience.
James and Mary