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Green roof becomes perfect spot for aquaponics grow bed  RSS feed

 
Dale Hodgins
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      My green roof plans and gardening plans have evolved dramatically in the last couple of days.

    I was  working on the plan for my green roof and realized that I have no use for sedum, hens and chickens,dry grasses and other succulents that thrive on green roofs in my area during our dry summers.

       Then it occurred to me that this surface contains all of the components required for an aquaponics grow bed. It contains a growing medium, has an impermeable membrane, has a gentle slope which brings all of the water, back to a collection point and it has plenty of sunlight.

    The additional cost to make the roof work as a grow bed is far less than if I created a separate space specificly for that purpose.

   Rooftops get quite hot and in my area that's a good thing since it will make the perfect spot to grow peppers, tomatoes, eggplant's and other crops which often suffer from lack of heat in the mild summer conditions of Vancouver Island. I could even see throwing a big plastic sheet over everything to stretch this season. My property sees very little wind in the summer.

   There will be quite a bit of water loss due to evaporation but I have plenty of water year-round. On hot summer days this evaporation will work like a giant swamp cooler which will moderate temperature within the house and around the rooftop deck.

    I will need to put up a good railing and I'll go with an extra thick liner. Flat boards or inset stepping stones will prevent foot traffic from damaging the liner. The roof will be somewhere around 3000 ft.². At some point a barn and implement shed will be built. I expect over time to have somewhere around 10,000 ft.² of roof area. By spending as little as one dollar per square foot more on my roof it will become one of the most productive areas rather than just a benign umbrella. And since the roof will have attractive plantings and a safety railing this leads to it being used for entertaining and other purposes.

    Although the property offers spectacular views from the ground it is often blocked by bushes and other growth. From the rooftop there is a view of the river valley and the rolling hills beyond. Until yesterday I only planned on going up there occasionally to check on the sedum and dry grasses.  Things change
 
John Abacene
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I might suggest that (A) A good Aquaponics setup is in a greenhouse of some sort, and that (B) A lightweight greenhouse on your roof would be naturally kept warm in winter.
But if there is a slop to your roof, ans especially if you are just growing stuff directly on the roof, it may be problematic, but I would be more concerned about the gradual damage that growing stuff on any roof, even a concrete one, results in. Tiny roots are tenacious at probing and picking into any substrate, even concrete, and if it ever goes below freezing, then the 'freeze and thaw' phenomena starts in as well.
I think Aquaponics is best done in its own grow bed, but that if you use a mix that reults in a very lightweight growing medium, and learn/design ways to continuously cycle the smallest dribble of water, it can work.  If your roof has a slope, maybe think like terraces or overlapping grow beds, so everything is level, yet still using the slope and gravity to bring the water everywhere it needs to go.
Keep in mind that with Aquaponics, one grow bed only needs to be slightly lower then the previous one, and that is properly designed and built, the water can be brought back up to the start again with just a bubble/air lift.
 
                        
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If I might suggest..you keep the fishtank on the ground. Water temperature can be an issue with most fish  and it would be a whole lot easier to manage it there than on the roof.  Might need a bigger pump to lift the water but that likely could be managed fairly easilly.

Sounds like a great idea!! the circulating water will also help to stop the roots from baking on those occassional really hot days. In many warmer countries flat roofs are used for all sorts of things. Here we tend not to think of roofs as anything but "hat" assets. Will you take some photos and keep us up to date?
 
Dale Hodgins
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  I definitely plan to keep the tank on the ground, not because of heat but because my tank is likely to weigh 20 tons.        That alone is reason to keep it firmly planted on the ground.
 
Dale Hodgins
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Dale Hodgins
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   Green roofs with plants on them are the longest lasting roofing material which I could possibly afford. This is not experimental. Millions of roofs use these materials. They're usually rated for about a 75 year life and the vast majority of these roofs have slope. The roots don't damage the liner. I'll use EDPM  liner and a good-sized pump since I'll want to move lots of water.        Any sort of light greenhouse would be crushed under heavy snowload in winter. On a large roof like this,some areas will be 20 ft. from the edge. This would require an extremely well built greenhouse.    I'll build several of these but not on my roof.    There's no shortage of great greenhouse sites.    The rooftop aquaponics is being implemented in order to utilize the grow bed that a green roof already provides.
 
Neal McSpadden
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I'm really curious how you'll set up the beds. Are you going to install baffles in the bed to make sure the water level comes close to the surface?
 
Dale Hodgins
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  I'll probably go with half-inch or three-quarter inch rock. Smooth glacial till, not the crushed variety. The media only needs to be deep enough to support the plants. Seedlings will be set with their roots, 1/4 inch from the membrane and I expect that roots may cause some damming of the water flow. I like the little terra-cotta balls which are sometimes used in grow beds, but I fear that they would be destroyed when exposed to hard freeze conditions.

    In order to get good saturation and not miss any spots I think some sort of sporadic flooding would be preferable to a slow trickle, which may channel and leave some areas dry. I don't want to get into placing any sort of baffle to interfere with flow since the roof needs to drain well during heavy winter rains.

  I expect the aquaponics system would be active March through October. Flat roofs get quite hot, so the roof will effectively be a trickle solar collector, which will warm up the fish tank much earlier in the season than would happen with a tank simply exposed to ambient temperature. In both early spring and late fall circulation will be curtailed until the roof warms up sufficiently in the morning. This will keep the water warm and extend the season at both ends.

  In summer, if I find that the return water is to hot, I'll have it dumped into a cooling tank, which is set above the fish tank. Water from the upper tank will spray into the lower in order to affect maximum aeration.

  During the winter, the fish tank associated with this system will be maintained within a greenhouse. Stocking rate will be greatly reduced, and I will use fish which are less temperature sensitive. The water will be slowly circulated through a bed containing cold tolerant vegetables.

  The rooftop grow bed will function much like any other gravel roof during the winter. I may try some kale or other hardy vegetables as a filler. On warm days, I may reactivate the pump, but would use it sparingly so as not to create a temperature shock for either plants or fish.
 
Tyler Ludens
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Rough or porous media, as opposed to smooth river gravel,  is supposed to harbor larger numbers of beneficial bacteria in an aquaonics system.   Smooth rock is supposed to work, but rough rock is supposed to work better.  

More info:  http://backyardaquaponics.com/forum/viewtopic.php?f=8&t=398&hilit=media

 
Dale Hodgins
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  That's a compromise I'm willing to make since it will be less likely to damage the membrane. One positive about glacial till is that there are many different types of rock which contain micronutrients.Some are absorbent,others arent.  I'll probably use some brick waste because it provides an amazing surface area for bacteria.
 
                        
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Maybe I'm misunderstanding something here but.. 1/4 inch for the roots seems pretty shallow...even lettuce will produce a lot of root to support the top growth..surely you mean to have the grow beds a little deeper than that? The least I have seen suggested is about 6 or 7 inches and even that seems to raise screams from the traditionalists who are convinced that a foot is the limit. I personally don't see why less  wouldn't work..people are growing stuff in roof guttering after all. but even those are considerably more than 1/4 inch deep!.

I'd lay money that the shallower the beds the more tweaking you will have to do to get the thing to function as well as you'd like it to.

Obviously weight can soon become an issue if using gravel in roof growbeds..something you might consider is what Green Power uses, i.e a mix based on coir. It seems this will discolour the water some but it's a lot lighter than gravel. It would handle the freezing without any problems but no idea how often or even if it needs to be replaced from time to time.  

As far as rock is concerned..it seems that some sorts will be a constant battle in terms of maintaining the correct ph. so you might want to be aware of/avoid those...
 
John Abacene
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For what its worth - I have been deep enough into Aquaponics that I have to start coming up with my own terms for things - one of those terms has been "Pseudo-Hydroponics" or in this case "Pseudo-Aquaponis"
Where this thread is concerned, what I would like to suggest is having a certain mix of media that has some qualities of soil for several reasons.
In Hydroponics, if the mix added to the water is wrong, a person can literally watch their plants start to die - usually this can be attributed to accidentally putting in way to much of something, usually by a new employee at a professional operation or something like that.
Also, in both Hydroponics and Aquaponics, if something happens to the water supply, whether that is a failed pump, a leak, or any of at least a dozen other possible problems, and you do not have contingencies to cover it, or are away from home for some reason, plants can also suffer or die.

In the concepts/terms I mentioned above, I have put together a couple of systems (my own hobby set-ups) using a pseudo-soil out of a careful mix of ingredients that will provide for minimal moisture and 'food' in case of some kind of system failure.  I tested it and found that with total system failure plants did well, or survived twice as long; and where worms were a part of the system, they too did well.  Just the right mix of media is not only beneficial, but can save your whole system if things somehow go wrong.

You mentioned the tank on the ground, pumping water up to the roof - this sounds great and will obviously work as long as you have the right method or equipment for pumping, but also keep in mind the stresses and pressures involved, which might not seem to be much, even if you pull the line and let the water run out and it seems to just run out, but does increase the actual stress on all components, especially the water line - if it is plastic type.  (forgive me if I have not remembered/read all your details) If you use copper line or any copper components, they also have impacts on the system that may either prevent future changes or kill something off.  I got pretty exotic with one of my set-ups, and it included fish and fresh-water shrimp that were sensitive to anything copper in the system, so I had to put it together with no copper anywhere, which was not easy with what I was doing.  However, once copper has been introduced into the system over time, later changing it out for something else still left the fish at risk because of all the traces of copper having become incorporated in the system in various ways and places - and even though they were only trace amounts, that can still have effects.
 
John Abacene
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Re: Rough or porous media: It is mostly about "Surface area", and also relates directly to the size of the system or growing beds.  One thing that can both be fantastic or a curse is lightweight lava rock available at many places where you would buy truckloads of gravel, etc.
On one hand, this stuff is pretty cheap, and has enormous surface area, and can work great;
However, the downside is that some places sell lava rock that was previously used for "Industrial filtration" which can mean toxic trace amounts. If you know where it came from, you know if you can use it or not.
May people have had a lot of success with just plain pea gravel. one thing that makes pea gravel better than larger gravel or smooth stones is that if you go probing around in the growing media with larger stones, and you have earthworms incorporated into the media, its easy to stress, injure, or kill the worms. This may not seem to be much of a concern, but it certainly doesn't help things at all.
With pea gravel, the plants come up easy, the media is easy to work with, it is far less likely to injure the worms if/when you are working with it, and has enough weight to hold the plants firmly. -andis also fairly cheap.
 
Dale Hodgins
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Pam wrote:
Maybe I'm misunderstanding something here but.. 1/4 inch for the roots seems pretty shallow...

I'd lay money that the shallower the beds the more tweaking...

Obviously weight can soon become an issue if using gravel in roof growbeds...

As far as rock is concerned...
 
Dale Hodgins
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  I didn't mention anything about building the bed one quarter of an inch deep.

      The roots of the plants will be placed 1/4 inch from the membrane so as to make adequate contact with the thin layer of water, which will flow down slope. The bed will be whatever minimum depth proves successful in their cultivation. Glacial till is the only readily available rock. Its benefits far outweigh any downside. It's also dirt cheap. The majority is igneous rock, some of which give off needed nutrients. If I find things are too acidic I'll mix in some oyster shell. If too alkaline I'll use rotting wood.

    The roof will be built to whatever standard is required for this weight. Wood costs me very little so I'll use whatever is required.

  The only aquaponics program at any Canadian University is one at Vancouver Island University, which is 8 miles from my door. I'm pursuing a partnership with them so minor issues like pH will be dealt with.

  My land has plenty of available resources none of which are coconut-based, so I'll pursue every avenue available with the resources at hand.

  Ultimately, I'd like to cover up to 3 acres with aquaponics greenhouses and hugelkultur beds, so I'm going to definitely try to use the least expensive, most readily available resources. After I've ironed the bugs out. It's quite likely that I'll offer my services to others and I want this unique roof to be one of the major draw cards to bring green building and agri-tourists to my farm.

  This particular roof is simply a pilot project for many more to follow.
 
sam12six Hatfield
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My major concern would be the fact that the relatively thin, loose layer of soil would not provide enough support for plants exposed to wind and rain.

Because of that, if it were me, I'd probably opt for a traditional sod type roof, just one that incorporated plants that can do the job of binding the roof and are useful to my personal situation.
 
                        
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well..... seems to me that it's an idea well worth trying..if it turns out to have too many hassles, really not out anything except time. It's not a bad thing to (in that case) end up with an over engineered roof The fish tank can always be hooked up to beds on the ground if necessary and the gravel reused in those beds or elsewhere. 

OTOH if it works, what a genius idea to have things doing double or even triple duty as roof, garden and entertainment area.
 
John Abacene
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Maybe consider this:
If you can seriously consider putting Aquaponics on the roof, then you can put them anywhere the sun will shine sufficiently. Think: What can you do or put on the roof that is better there than anywhere else?
A roof potentially has a lot of surface area, and a lot of exposure to sunlight, and is higher than the ground.  I would think the best things you can do with a roof would be solar panels and solar water heating, etc. but that is obvious.  A roof can make a great deck.

I've always liked the idea of an observation deck, enclosed with large panes of glass, like using sliding glass door panes, so that I could watch lightning storms with a great view while staying dry and comfy, or for watching meteor showers or the northern lights.
 
Tyler Ludens
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I had a small amount of limestone pea gravel in my aquaponics which appeared to make the system far too alkaline.  So I personally would avoid pea gravel unless you know for a fact it isn't limestone.  I'm using granite gravel which seems to be doing ok.   

Personally I love the idea of an aquaponics roof.  I love the idea of green roofs and multi-purpose green roofs would have to be just that much more terrific.  What about an observation platform surrounded by plants?  That seems pretty darn cool to me.  You'd want a place where tourists could stand around observing the aquaponics roof anyway. 

 
Dale Hodgins
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creteman wrote:
Maybe consider this:
If you can seriously consider putting Aquaponics on the roof, then you can put them anywhere the sun will shine sufficiently. Think: What can you do or put on the roof that is better there than anywhere else?
A roof potentially has a lot of surface area, and a lot of exposure to sunlight, and is higher than the ground.  I would think the best things you can do with a roof would be solar panels and solar water heating, etc. but that is obvious.  A roof can make a great deck.

I've always liked the idea of an observation deck, enclosed with large panes of glass, like using sliding glass door panes, so that I could watch lightning storms with a great view while staying dry and comfy, or for watching meteor showers or the northern lights.
 
Dale Hodgins
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There will be a rooftop deck, and I intend for it to be surrounded by a vegetable garden.

    I don't post my plans with a view to being talked out of them. Instead, I seek constructive ideas on how it can be done better.  The rooftop aquaponics thing is a done deal for me. It's how I plan to construct at least one roof. I won't start off with a 10,000 ft.² roof  and I won't invest my life savings into it. But I do intend to build a roof in this manner. That's a given for me, when I have a good idea I carry it through to some sort of conclusion. 

  I was saving this for my gravestone, but have decided to share it here.

    "The most abundant and easily accessible information available to us are all the reasons why it can't be done". Dale Hodgins - Inventor.       
 
Dale Hodgins
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  I won't be attempting to grow anything tall, although as stated earlier, I receive very little wind. There are days when I could stand a sheet of plywood on edge and come back to find it there an hour later. . When I use my chainsaw I have to keep walking to avoid breathing the fumes since they don't blow away some days.

  Rain is relatively rare during the growing season. Most of our rain comes in the winter months when the roof would be planted out in kale or some other crop that thrives on neglect. And I could just leave the roof empty in the winter. A rubber lined roof with gravel cover can last for generations.

  I'm probably going to favor things like squashes, tomatoes which are allowed to sprawl, chard, eggplants, peppers, cucumbers, melons, sweet potatoes and other plants which appreciate heat.

    Many of the fruits from these plants will rest directly on the growing medium and will be less likely to puncture under their own weight when resting on smooth stones. So I won't be trying to encourage deep flooding of the bed as this would not benefit the various fruits. I hope to produce most root growth in the zone 2 inches from the liner. The remaining rocks would work as a mulch and serve to separate exposed fruits from the moisture below.

  The pond water may be run through a much deeper gravel bed, which would sit beside the fish tanks prior to being pumped to the roof. Worms and other beneficial creatures could break down fish waste before it is sent to the plants. It's likely that bacteria will do well throughout the system, but worms may not appreciate the thin moist layer and possible temperature swings which are likely in a rooftop environment.

  If I find it difficult to grow certain crops, then I won't. I've always preferred a survival of the fittest policy when gardening. Most of the crops I've mentioned do well without support. I'll try everything, but I'm not worried if I end up, finally settling on only a few types of vegetable and fruit since this would still be far more productive than producing dry grass.

    A flattish garden like this is not as efficient to harvest as steeply sloped hugelkultur beds or other raised beds, so I will steer clear of things like peas, beans, and other crops, which require lots of fiddling and searching during harvest. Large things like melons, beefsteak tomatoes, squash and eggplants are easily identified. I'll even choose varieties noted for bright colors so that they don't blend with the foliage in what is likely to be quite a thicket.

    I created a thread in the permaculture section concerning the use of hugelkultur beds in an aquaponics system. I'll try this on either a portion of the house roof or on the roof of a small outbuilding.  hugelkultur beds would only be run from top to bottom on the slope and not across slope, since I don't want to create a situation where the bed becomes an ice dam in winter. The valleys between beds would allow for snow melt and drainage.

  Very occasionally, maybe every 10 or 20 years, we get a huge snowfall with six or 8 feet accumulation of wet snow. Therefore, our buildings must be built strong enough to support this load. By comparison, the loads imposed by the gravel and plants are not that great. The actual increase in weight is probably 25% of the weight of this snow load. I'm going to build a safety margin of up to 100% so that  the large quantity of gravel on the roof never becomes an issue structurally.
 
John Abacene
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-P.S.- I knew someone who built a small greenhouse on the side of his home where his vent for the clothes dryer was, and ran the vent for that dryer though the floor of that greenhouse on its way out, which gave an occasional boost to the warmth there, which saved a little on utilities, as he had some kind of thermostat for the greenhouse, which was able to compensate for the added warmth.
- Just a random thought.
 
                        
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Strawberries apparently do well in an aquaponic system and  might be tough enough to spend the winter  up there. Certainly they do in the ground, not sure how that would translate to the roof situation.
 
sam12six Hatfield
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dale hodgins wrote:
There will be a rooftop deck, and I intend for it to be surrounded by a vegetable garden.

    I don't post my plans with a view to being talked out of them. Instead, I seek constructive ideas on how it can be done better.  The rooftop aquaponics thing is a done deal for me. It's how I plan to construct at least one roof. I won't start off with a 10,000 ft.² roof  and I won't invest my life savings into it. But I do intend to build a roof in this manner. That's a given for me, when I have a good idea I carry it through to some sort of conclusion.   


No one's said, "That's crazy!! It'll never work!!", just that going with the green roof you originally planned and searching for a plant that would be useful to you might make more sense than shifting to a different system altogether.


dale hodgins wrote:

   I was saving this for my gravestone, but have decided to share it here.

     "The most abundant and easily accessible information available to us are all the reasons why it can't be done". Dale Hodgins - Inventor.         


While I agree with thinking outside the box, if I had to pen a quote in rebuttal, it'd be something like:

"The people least likely to process new information are the ones convinced they already know it all." sam - rebutter

Anyway, philosophical people can exchange "Nothing ventured, nothing gained." and "Look before you leap!!" all day. The point of people posting possible concerns isn't to keep you from doing it. It's just to be sure you've thought of a solution before those concerns become a problem. Good luck with it.
 
John Abacene
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Interesting point.
I have learned through a lifetime of designing things that the most important part is anticipating Murphy's law - figuring out anything that can go wrong, and re-designing to compensate.
 
Dale Hodgins
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  Thank you gentlemen for your input, I think we've all agreed to agree to disagree on certain points. That was a cathartic little exercise,glad I got that off my chest . And we did it all without receiving a scolding from Paul.

  Now let's get back to reinventing aquaponics.  I plan to eventually do a few acres of this, so I'm not worried about going too far wrong on any given project. This project is probably better suited to a small shed during the first year. Then, if all goes well I'll do a grander version.

 
Dale Hodgins
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  I learned a good lesson today which could have affected this thread. I decided to Google rooftop aquaponics. And I got lots of hits. As it turns out, none of them were even close to what I'm suggesting here. They were all tank and grow bed situations on top of big commercial buildings  so were simply using the available space but not using the roofing membrane as the base for a system.

    Just imagine if everything we've talked about so far were there for the taking. Wouldn't I be a dummy?    From now on I'll Google any new idea before going through all the mental gymnastics of imagining it from the scratch.

  I quite often see new threads started on this forum which relate closely to another that was posted a few months back. So it makes sense to have a look at all of the topics going back several months before posting some idea as being original. Before I got into using a computer last year I thought I had invented cordwood/cob. I had been working on a design for a Russian fireplace which looks a lot like a rocket stove without a heat riser and several years ago I called my daughter to inform her that I had invented a new drink combining coffee and hot chocolate. She said "dad, it's called mocha" and you need to get out more.    

  So from now on I plan to Google  and to check old threads before posting a new idea. If I post something that's been covered please direct me to the other thread. Unless my idea is significantly different I will immediately remove it and save the forum from redundancy.

  This post should probably be in a different section called forum guidelines or something. I've only put it here because I discovered the error of my ways while searching  rooftop aquaponics.
 
Neal McSpadden
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Due diligence is always a good thing .
 
Dale Hodgins
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I have a couple of natural amphitheaters which are facing South. One appears to be totally natural perhaps created during a landslide and the other is obviously the result of gravel extraction. Both are areas with very little wind and full sun exposure. One of these will be the site of the first greenhouse and at the rear, Northern edge I'll build a living quarters with a green roof. This will be where I'll test out everything I've posted so far. The biggest amphitheater sits above my entry road. I may install some sort of stage in this area since it's a perfect spot for hosting entertainment and it is central to the area being developed as a public park. I think an aquaponics greenhouse in this area would make an excellent educational facility as well.
 
dave brenneman
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Dale Hodgins wrote:several years ago I called my daughter to inform her that I had invented a new drink combining coffee and hot chocolate. She said "dad, it's called mocha" and you need to get out more.


Thank you; I got a very good laugh from that one. You were right; it is a tasty combo, regardless of who invented it.
 
Casey Halone
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I like that these grow beds could draw heaps of the heat into the fish tank which the fish might enjoy and save on water heating vs letting the heat enter your house THEN attempt to cool the air in your house. Stacking functions like this is very permaculture.
 
Dale Hodgins
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Air conditioning is not much of an issue here on Vancouver Island except for a few weeks in the summer. I complain bitterly if the temperature goes over 80 Fahrenheit. But in the process of thinking anything like this through, helps consider those in other more harsh environments. The air-conditioning effect could really come into its own in hot humid climates where the roof would effectively be a giant swamp cooler.

Places like the American Southwest would not benefit so much from any air-conditioning effect because the need to conserve water would result in design changes which would reduce evaporation. But still the huge thermal mass of the growing medium on the roof would prove to even out temperatures in areas with a large diurnal range.

For me it will be important to bring water up to 75 or 80°F in the spring and to maintain those temperatures into the fall so as to create an acceptable environment for fast-growing warm water fish. By adjusting water flow according to roof temperature I'll be able to extract heat from the roof and move it to my water tanks during these seasons.
 
Dale Hodgins
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Unfortunately the continuity of this thread has been ruined by deletions. Too bad, some of it was classic mental ward stuff. Mostly dire warnings to avoid innovation.

Although immediately enthusiastic, I haven't heard from anyone at the university since the original call. Our fisheries studies are often corporately funded. A system like this might be a hard sell because it is more archetectural than fishy. So, I'll build it and in time they may come on board.
 
Andrew Parker
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Dale,

I researched green roofs when I was planning my second story addition a few years ago. I didn't do it because of added cost.

You might want to look into expanded clay. It serves the same purpose as perlite. It is still lightweight, but it won't blow away. It holds water and liquid nutrients. Biggest drawback compared to the materials you listed is that it isn't free. You might also put a layer of rigid mineral wool just above your membrane, to facilitate drainage -- also, not free.

I live in a high risk earthquake area and I get a little paranoid about roof weight. I think that a green roof is a viable option, if the weight can be kept down.

In the neighborhood I grew up in, there was a house with a flat roof sloping to a central drain and rimmed by two foot high parapet walls. The idea was that in the summer the drain would be closed and the roof covered with water. Evaporation would cool the roof, as well as eliminate solar gain. I don't know if it worked. Sometime in the past 30 years it was covered with a conventional pitched roof. My guess is that newer owners decided replacing a worn membrane was too expensive, or they were also paranoid about roof weight.

I don't think that a green roof would use more water than an evaporative cooler, which are fairly standard in the arid areas of the Western US. They do use a lot of water, but they keep the house cooled for far less expense than central air. A green roof here where I live would probably not be enough to keep a house cool without some help. In your area, it should be enough to keep it more or less comfortable, if the roof is the single largest source of solar gain into the house during summer.

What would be the power use of the recirculation pump? Could it be run with photovoltaic panels?
 
Dale Hodgins
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Strength concerns are not a huge issue for me since I have an endless supply of cheap wood. Every 20 years or so we get hit with 6 ft or more of wet snow. The additional weight of the green roof adds less than 25% to the design weight. I'm going to build strong.

I'm going with EPDM rubber, well protected from puncture and other damage. The growth medium will be mostly gravel. Rubber roofing covered with pea gravel is a proven durable technology. I'm simply adding some plants and water flow on top of it. Over time my gravel may clog up with organic debris. It can be carefully gathered and screened if desired.
 
Andrew Parker
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It sounds like it should work. I look forward to the pictures.
 
Dale Hodgins
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I agree. Here's the link: http://stoves2.com
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