(urban) rooftop greenhouses

[peteMc]

anyone growing in or have experience with a rooftop greenhouse? I've gotten some encouragement from my landlord to build one, was wondering if there were folks here who might have thoughts about it, tips and tricks, anything at all to share....

i'm reading up, looking around at materials, ways to heat it, etc. etc., just thought i'd throw it out here and see what anyone had to say

thanks
peteMc

[LJA]

pete, I'm not sure what your weather and climate is like out there, but my experience with urban living reminds me that rooftops can get awfully hot, especially in the middle of summer. In SoCal and VA anyway, it wasn't uncommon for temps to reach 120 and even higher on a rooftop, especially with no breeze. In a greenhouse (which already traps light energy and converts it to heat), I would imagine the temp up on a rooftop would have reached a level that no amount of cooling could reasonably have been provided that would have reduced the heat down to the (typical) 95 above which you really don't want to keep orchids.

Again, I have no idea what your particular rooftop conditions are like, so that caution may not apply. But do you have a Hi-Lo thermometer that reads and holds the hottest and coldest temps in an area? You might set one up there under some shadecloth or screen or something so you'd have a general idea of conditions before you dove into the project. Other than that, if you can provide a water and electrical source, I think you'd be able to create a really nice growing space.

[kewpie]

did anyone see the orchid documentary a while back on pbs? well, i mention it because they show an old gentleman with an orchid greenhouse on top of an apartment in new york. i dont know how he cooled it in the summer (im sure new york gets as hot as mass. in the summertime) but i know it can be done.....cuz tv told me so.

[peteMc]

I am having that concern as well; it is a black rubber roof and retains a lot of heat. however, we are regularly quite breezy, if not right windy, here - I'm not all that far from both the harbor and the Mystic River- so I think some temp tests might be in order, that's a very good idea Louis. I'll be running them this weekend, it's supposed to be pretty hot again.

the difficulty is actually twofold. to build insulated enough for some fairly cold winters, that can also be cooled for hot summers.

I have been looking into a saltbox/solar slope design, that would have polycarb only on the long slope, short slope vented. Insulation works both ways, obviously, so if the temps aren't too high a swampcooler might be able to handle it. Utilities are not a problem, both water and electricity are close by, and use of the existing roof drains for runoff. I'm a long long way from commiting to the project, I have a lot of reading and research to do, but the possibilities are exciting.

thank you for your responses.
peteMc

[Tanya]

Some of my orchids, no, most of my orchids are growing on the roof. Not a greenhouse, I can't afford to build one. It only have a black nylon netting for shade, and believe me, its really very hot during daytime. But the orchids are doing fine. The orchids are: 3 types of Vanda, 3 types of dendrobium (no nobile) 4 types of oncidium, 4 or 5 types of catt... I can't remember lol....and one brassia... the vandas are exposed to direct sun most of the day, so as the dendrobiums.... and they are all happy, much happier than the paphs that are inside the house.... Oh I forgot to mention that there are also 2 types of paph among the orchids on the roof.....one is a true specie... a native to Philippines..temp there could reach well over 40 deg C but breezy and the paphs just love it....

Tanya

[peteMc]

you were right, Louis, it's very hot up there. I'd be paying as much to cool it down in the summer as I would to keep it warm in the winter. too bad, had me pretty excited for a bit.

have to work with what i've got. still it was good to make a start on the research, never know what might happen later.


happy growing all
p

[LJA]

Glad you checked it out (I personally have a terrible history of diving into things without a second thought because I'm excited, only to find out too late that something isn't going to work....) But I'm learning not to do that quite so much.

...sort of.

[Forrest]

I wouldnt give up that easy. That is an awesome opportunity to have a GH in the city. I would start looking at energy star Air conditioners and like triple wall poly or some sort of highly insulated GH material. You would tehn need to run a humidifier to compensate for the moisture the AC unit sucks out. I would imagine that heating would not be that big of a drag if it is properly insulated to begin with.

I would go for it personally

[peteMc]

lol, thank you Forrest. this is about the response I'm getting around here from folks, about 50-50.

i'm going to continue to research/read for the winter; there are a couple people close by who are operating gh's, although not on their roofs, that i can talk to. i'm still leaning toward a no-go, having seen what I have to work with.

but i am enjoying the learning.

p

[LJA]

Well, there's no question that it's do-able, I think it's more a matter of cost. If money is no object, then sure, go for it. Our greenhouse is all double wall polycarb, and that was the single most expensive part of the whole thing. We paid over 8k for the polycarb alone. A quick search for *triple* wall poly turned up an average of $210.00 for a single 4x12 sheet. I don't know how big you were thinking, but that'll add up in a hurry--you don't want to make any mistakes when you're cutting your sheets!

As far as AC goes, 4 summers ago we had a really bad heat wave where it got to be 115-118 in the middle of the day. Our KoolCell (swamp cooler) runs the full width of the GH at one end, and with that kind of moist heat, it wasn't doing a thing. I had a 3-ton AC unit installed, just to save the plants, and I rigged it so that when the AC kicked on, the fans pulling outside air in kicked off.

The AC wasn't strong enough to compensate for the greenhouse effect, and this was a unit designed to cool a 3000 sq foot dwelling. Temps just kept rising. The only way to make it barely work maintaining temps at about 105 was to keep the fans on, exhausting hot air, *and* keep the AC going, trying to cool it. You can bet the electric company loved us those 2 months, and the AC unit cost over $2500, installed and ducted. Our greenhouse is 18 x 32, just over 500 sq feet.

In general, AC is going to pull moisture out first before it does any significant cooling. It's only when the air is already dry that it can really function at intended capacity. So if you humidify to compensate for the AC, the AC will be doing less of a job than it can, and so will the humidifier--you'll have two things running at cross-purposes, and paying more to operate both of them.

Again, it's a question of money--I guess I was imagining you building something like a 10x10 structure with a fan at one end and a swamp cooler at the other, maybe heating it with a couple of those oil filled electric radiators in the wintertime. I'm certainly not trying to discourage anyone--if there's a will and a wallet, there's a way. I'm only pointing out some of the practical things that need to be considered with a project like that, based on my experience, and I just have a feeling that, unless you're willing to go to some pretty extensive lengths, the "hobby greenhouse kit" you buy from somewhere and perch on your rooftop is going to end up being little more than an orchid-broiler in the height of summer.