So I have been browsing the site for some time and gathering info on greenhouses, and now I am on the cusp of taking the plunge.

I have a small balcony on the southeast corner of my home that goes unused for the most part. It gets lots of direct sun until 3-4pm and then the shadow of the house takes over. It is currently covered with black roofing which contributes to the high heat it experiences during a sunny day. My thought is to create a greenhouse out of this space.

I recently met a carpenter who does work for a local nursery. He took a look at the space and gave me an estimate. He said he would put in a side vent plus a window and also have a roof vent that would open and close automatically with temperature. He suggested putting in a light-reducing fabric (i don't recall the type) and a fan to help cut down the heat in summer. This would be like a shade cloth that could be pulled up and down as needed. The material for the walls and ceiling would be similar to this: http://www.farmwholesale.com/panels.php3 Other thoughts I had were to put down some light-colored matting during summer so the black roofing doesn't absorb as much heat. In winter I assume the roofing would be beneficial for heat absorption. Also, he suggested using a portable oil filled radiator for heat in winter.

The area would be approx 7'Wx12'Lx10'H. I realize this is small and that cooling it in summer would be the challenge rather than heating it in winter (which may also be a challenge). I don't have room in my yard for a greenhouse of the same size and prices for kits are comparable or even more expensive than his estimate. I primarily need a place to overwinter my citrus and other plants, as in summer I can bring out all the plants into the yard for direct sunlight and better temp control. I would like this to be a place for plants to continue to grow and flourish through the winter rather than just barely survive as in my current situation.

So my questions are these:
1) Do you think there would be enough light there throughout the year to nurture citrus fruit through to ripening? Remember the west and north sides are blocked by the house. (p.s.- I also have a 400W grow light whose ballast switches from HPS to MH)
2) I am not entirely sure how well this would hold heat during the coldest months and if I would realistically be able to control the temps. I simply have no experience with greenhouse growing.
3) Do you honestly think it is worth it to go through the construction if it doesn't really gain me much in terms of growing control?

Here are a few pics of the area to help visualize what I am talking about:


This is looking down on the surface of the balcony
A look at the roof overhang
Looking North from the yard. The West side has the door to the house

Any and all advice is helpful and appreciated. Thanks.

Can anyone give me any feedback? I'm sure I can learn from your experiences with small greenhouses.

I notice when reading the link to the glazing, that the type shown was made from twin wall polyethylene. All greenhouse construction uses twin wall polycarbonate. Also it is never overlapped, rather it is held in place with an aluminum H-channels. The light transmission of polycarbonate is 82 percent. As far as the amount of heat saving it is not much as the R value of twin wall is only 1.6. My greenhouse uses twin wall polycarbonate for the side walls and end wall, and air inflated double poly for the roof. One item you must make ABSOLUTELY SURE of is whatever glazing you install, it is Teflon coated on one side for sun protection against yellowing and degrading. All greenhouse glazing are Teflon coated. The amount of light should be fine for citrus. For a small greenhouse, the use of 1/2 - 1 inch silver sided polyurethane insulation sheets (4 X 8 or 4 X 10) erected against the glazing at night greatly reduces the heat bill. - Millet

Chops
I see a problem with the window air conditioner unit. Is it possible to move it to another window in the same room? You don’t want the condenser side of the air conditioner inside the greenhouse. The AC needs a source of ambient air for efficient cooling. The heat from the AC may be a problem for the greenhouse and hotter temps will increase cooling cost and mechanical failure of the AC unit.
Karl

Hi Chops,

The panels you link are polyethylene. PAR transmittance (the amount of light radiation that contributes to photosynthesis) is usually under 80%, in the 70+% range, but this light will be well-diffused and even. The big problem with polyethylene is its LIR transmittance. In contrast to most other GH glazing materials, polyethylene is not opaque to long wavelength infrared. So what? you might ask. Well, that opacity is important, because the warmth in a GH that accumulates during the day from absorbed light (PAR) is not reemitted as PAR, but as LIR. You want the glazing to be opaque to that radiation, so the heat stays in the GH. That is the essence of how a GH works...the glazing transmits one type of radiation, then traps that radiation because the glazing is opaque to the LIR. Glass and polycarbonate are both opaque to the LIR wavelengths.

Now, polyethylene can be treated with an IR additive...the Solexx may already have this property, but I don't see any mention of this on the website. This IR additive, also available on polyethylene sheets, will make the PE glazing relatively opaque to LIR and help control your night time heat losses as well. Something to check on...

I don't really think Millet was saying that all GH are built of PC...there are, of course, a variety of available glazing materials for greenhouses, including polyethylene, glass, polycarbonate, even PVC in some areas of the world. My GH is all glass.

Now, is this proposed GH attached like a lean-to structure, attached to the house? What is underneath this little deck? It may be helpful to insulate the floor, esp if the area underneath is not heated. If attached to the house like a lean-to structure, then your north wall is already insulated. I don't think that heating this structure would be too burdensome, really. You may still need a ventilation fan, because small GH spaces heat up quickly, and passive ventilation is often not adequate.

I think it is a neat idea.

SB

Robert, very good thread. As far as I know, at least in commercial greenhouse construction, double air inflated poly is the most cost effective heat savings glazing, without limiting the light available to the plants. By far the most valuable commodity in any greenhouse is always the usable light. - Millet

I might have missed it in the posts or photos, but is there something under the balcony or is it just hanging out into space?
Even polycarbonate is very heavy and a greenhouse structure on that balcony might be just too heavy for it. You might also think about where any extra water from your plants might be going.
I'd try to get the greenhouse on the ground if possible.

Thank you all for your replies.

I left a message with the guy who gave me the estimate and I plan on asking him questions on the topics all of you brought up. I do not know what the glazing that he uses is actually made of, I only used that link to the Solex as a reference of what it looked like to me. I will make sure to ask if his material is polycarbonate and if it is coated.

As far as the balcony, think of it as a rooftop. It is on the second floor and it is over a closed part of the house (like a cube with a notch cut out of the corner). The room below is heated but with a small radiator. (In winter that room hovers around 60F.) The greenhouse will be like a lean-to structure but closed in and attached to the house on all sides. To my knowledge there will be no overlapping of glazing- it will be built like a wall to a room. He mentioned he would match the angle of the roof of the greenhouse to the roof of the house itself. Any weight to the structure would be amply supported by the house. Putting a greenhouse on ground level is not an option given the small yard space. The air conditioner would move to another window altogether. I will have to try that idea with the insulation for winter.