A rooftop lawn (or at least the idea of one).

Discussion in 'Small Space Gardening' started by rossferguson, Aug 10, 2005.

  1. rossferguson

    rossferguson Member

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    Hi all,

    We're in a rooftop apartment here in Burnaby that's got full south and west exposure, and we want to use the 18 x 16.5' empty space of the roof next to our deck for something a little greener than the tar-and-gravel that's currently there.

    We were thinking of setting up some sort of lawn arrangement up there, using an elevated base (perhaps shipping pallets as a base), then landscaping cloth, then a layer of topsoil a few inches thick, and then laying sod.

    Does this sound feasible? Or are we right out to lunch? Information on setting up rooftop gardens seems to be relatively hard to come by - most of it seems to be geared towards container gardening, which I've got down pat.

    Thanks for any suggestions you might have!
     
  2. Daniel Mosquin

    Daniel Mosquin Paragon of Plants UBC Botanical Garden Forums Administrator Forums Moderator 10 Years

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    I suspect this is the resource you are looking for:

    Green Roofs for Healthy Cities.

    Incidentally, we were hoping to get some green rooftops here at the garden as replacements for our current roofs, but the structures are not built sturdily enough to handle the weight. I think the consensus, though, is to have green rooftops on any new construction if/when that happens.
     
  3. Carol Ja

    Carol Ja Active Member 10 Years

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    You also might want to get a stuctural engineer to make sure that your roof can hold the extra weight. There are a few books out there on the topic though.
    Carol Ja
     
  4. whistler

    whistler Member

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    Hi,
    Total green roofs or eco roofs are a sort of sustainability concept. Total buildings under a green roof benifit from keeping heat in and staying cool, but primarily aid in absorbing and detaining rainfall. [This is a vague meaning]. Soil media is very different, from the say normal container plant medium. Very light weight, lots of pumice and has to have a impermaeable membrane that protects the building.
    As for plants, grass is a no!! U want something that doesnt require alot of water,has fibrous roots, spreads fast. Try Low growing Sedums,Thmyes, Snow in summer
     
  5. Puddleton

    Puddleton Active Member 10 Years

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    Check out this website for some amazing and effective technology that will help your roof garden quest. I have no affiliation with this company, some colleagues have used it with excellent results
    http://www.fytogreen.com.au/
     
  6. Diane W.

    Diane W. Active Member

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    Not sure of the ins and outs of roof gardening regarding weight, watering, etc. but
    you might think about scree gardening - virtually no watering required and you can
    grow a variety of plants, much more interesting than just grass and no mowing required!
     
  7. Chris Klapwijk

    Chris Klapwijk Active Member 10 Years

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    Location:
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    logistics

    To cover your area with one foot of soil:

    Soil weighs app. 80-120 lbs. per cubic foot, depending on constituent materials.
    Water weighs 62.416 pounds per cubic foot at 32°F

    18' x 16.5' = 297 square feet (= 42,768 square inches) of roofdeck

    18' x 16.5' x 1' = 297 cubic feet (= 11 cubic yards) of soil

    297 cubic feet x 100 lbs. per cubic foot of soil = 29,700 lbs

    Allow 25% by volume for moisture: 297 cubic feet x 25% = 74.25 cubic feet of water

    74.25 cubic feet of water x 62.416 lbs. per cubic foot = 4,696.804 lbs

    4696.804 + 29,700 = 34,396.804 lbs. (nominal 17 tons of raw materials)

    34,396.804 lbs. / 42,768 square inches = 0.8(0426496445940890385334829779274) lbs. per square inch

    Most roofs would be able to support 0.8 lbs. per square inch in additional weight, provided it is evenly distributed.

    Your pallets would re-distribute the same amount of weight over a smaller area, double-faced pallets are not 100% covered on either side.

    Macroscopically, gravel has an uneven surface, with some of it higher than others. Microscopically, gravel has very small surface areas for direct contact with a pallet. All the weight would be carried by small surface areas of only some of the gravel, making for very uneven distribution and sure to inflict damage to the roof deck.

    Container growing is your best bet given your situation.

    Attached are some pictures of a 2,000 square feet rooftop garden overlooking Coal Harbour.

    To support the weight of 10 tons (2,000 gallons) of water in the 3 koi ponds, 30 tons of soil, another 10 tons of water in the soil, the rockwork, and the plants themselves, the roofdeck was re-designed to be able to withstand 250 lbs per square foot from the original specification of 100 lbs.per square foot.

    Biodegradability of the soil is another major consideration.
    Most organic material decomposes fairly rapidly, however, the coconut fibre soil mixture used in this garden is showing good resistance to decay.

    This garden is the only private Canadian garden to be featured in "Green Roofs: Ecological Design and Construction", 2005, Schiffer Publishing, Ltd., ISBN: 0764321897.
     

    Attached Files:

  8. Puddleton

    Puddleton Active Member 10 Years

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    Compliments to Chris for the time you've provided and information you've delivered.
    I can see nothing but major nightmares using pallets. We use a product called Atlantis drainage panels or cells. Google "invisible structures" for some excellent concepts on drainage and load dispersal. By no means am I trying to plug or sell this product below. The links provide some excellent tips and will compliment Chris' information
    http://www.fytogreen.com.au/docs/saturatedweights.pdf
    http://www.fytogreen.com.au/docs/Roof Garden Tree Planting.pdf
    http://www.fytogreen.com.au/docs/Paddington Roof Garden.pdf
    http://www.fytogreen.com.au/docs/hydrocellhardfoamrg30.pdf
     
  9. Candy

    Candy Active Member

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    I worked in a building with a rooftop garden. We had constant leaks into the boardroom below the planted area. After twice replacing the non-permeable coating, the garden was eventually re-designed using containers.

    I believe the green roof idea has to be part of the original design of a building, or at least a major engineering retrofit.
     
  10. Ralph Walton

    Ralph Walton Active Member 10 Years

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    0.8 lb per square inch = 115 lb per sq. foot, definitely a structurally significant load! I would not encourage anybody to add this load to a roof without an engineering inspection and assessment.

    Ralph
     
  11. Chris Klapwijk

    Chris Klapwijk Active Member 10 Years

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    Ralph, kudos to you.

    I noticed the mistake I made after Puddleton's reply, but decided to leave it to see if anyone else would notice.
     
  12. Puddleton

    Puddleton Active Member 10 Years

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    Chris, seeing that you wrote it with such confidence & the fact that Maths is one of my weaker points, you still win gold
     
  13. Carol Ja

    Carol Ja Active Member 10 Years

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    A friend of mine here on the island is building a hemp bale house, he is going to put in a 'green roof' as he called it. As his walls are hemp bale width thick along with post and beam roof, I'm sure he'll be fine with the wieght (he has already talked to the engineer) My concern would be more about the moisture, with all those bales, and West Coast rain, holding water up close to the house. Would molds not be a problem.
    Carol Ja
     
  14. Ralph Walton

    Ralph Walton Active Member 10 Years

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    Moisture is a concern here for a bale house whether or not you have a sod or other green roof. A bale structure in a drier climate will average out to have less moisture in it. The type of roof cover will have much less effect than for instance the size of the overhangs and the the orientation to and shelter from prevailing wet season winds. I'd say go for the green.

    Ralph
     
  15. Ian J. Egloff

    Ian J. Egloff Member

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    Sounds like a lot of good advice already. Get an engineer or keep it simple and small.
    I do green roofs for new buildings.
    I've thought about retrofits. It is not easy.
    You may want to look at lots of small pots that can be rested on pavers so you can see if the roots are trying to get into the roof membrane.
    Maybe float a wood deck on pavers every 48" to allow drainage.

    Do not to put wood, soil or plants in contact with the roof.

    I have always wanted to do a low water use garden bed with a layer of EPD roofing under a drain matt under sand under filter cloth under soil with plants. The idea is to slope the water proof membrane to a collection bucket and re-circulate the water to minimize waste. It would take a lot of effort to do this or any garden bed on a roof.

    Any thing you do on an existing roof must be raised to alow water to flow under it & removable so you can clean and inspect for damage once a year.

    Good luck
    Ian
     
  16. Weekend Gardener

    Weekend Gardener Active Member 10 Years

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    Those calculations are made without considering the weight of the occassional, but not insignificant, snowfall that we might get in the Lower Mainland.
     
  17. stargrass

    stargrass Member

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    After all that has been said, i'm going to feel like i'm going off on a real tangent here, but...
    What about some bamboo in containers, variouse sizes from extremely tall to ornamental additions to other containers, plus a variety of shrubs, trees and miscellaneous containers, river rock and some stepping pavers... et voila! A virtual sanctuary with out the worry of damaging an unsuspecting structure ( I first thought 'leeks').
    Your idea(s) for a green roof are fantastic! I offer alternative considerations...
    Have Fun!
     
  18. Puddleton

    Puddleton Active Member 10 Years

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    Heya Stargrass
    Your ideas sound wonderful. If the roofgarden was my own, I would use bamboos also. When I recommend plants for balconies or roofs for clients, I always suggest plants that will survive if allowed to dry out completely. Imagine three days of heatwave conditions and the irrigation system happens to break down during. Bamboo is quite expensive and stresses very badly when it hits wiilting point (massive leaf fall with ratty looking surviving leaves). Bamboo regardless of whether its invasive or non invasive has a very busy root system. Your drainage system will definately become fouled and blocked with bamboo roots which will lead to significant remedial works in the future.
    If you are being paid to develop a roof garden or any other garden for that matter, your duty of care is to ensure that all species thrive without causing detrimental effects upon the garden and building infrastructures
     
  19. stargrass

    stargrass Member

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    [If you are being paid to develop a roof garden or any other garden for that matter, your duty of care is to ensure that all species thrive without causing detrimental effects upon the garden and building infrastructures[/QUOTE]

    Would you not be able to keep the root systems contained in larger containers? Large containers over a healthy layer of river rock? Would this have similar impact as a 'green' rooftop on an older (1970's) low rise building? Especially in terms of the degeneration of buildings integrity, leaks, etc.

    Yes, bamboo is choice, especially when it is tall, strong and healthy!!!
     
  20. karms

    karms Member

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    I know nothng about the technical aspects of turning roof-tops into planters, but a word of caution. After 15 years, we just replaced our roof-top lawn with wood decking. The lawn was part of the original building design, but eventually there were issues with water leakage and great difficulty in determining the source of the leakage since the lawn can't be lifted to take a look. I'd say do thorough research and consider the long-term implications.
     
  21. stoneangel

    stoneangel Active Member VCBF Cherry Scout

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    http://www.answers.com/library/Conversions-cid-2011316081

    Hope this might be helpful when trying to figure out weights. I also asked a lot of other questions concerning weight and rooftops. Also found the site useful for figuring out the actual weight of my aquarium.

    A note about using river rock for drainage: perhaps you could substitute packing peanuts or vermiculite.
     

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