Garage - Greenhouse Conversion

14 years ago

Greetings all ... I am kicking around the idea for a greenhouse project that I'd love your collective input on. I need a GH; I need storage. Our HOA is very restrictive and not interested in small outbuildings or poly structures being on the property. As a compromise I'm planning on a ~400 sq ft garage, heavily windowed on the north and east with skylights to augment. I'll do a full on concrete foundation with drainage and the exterior will be stucco and composition shingles. Aside from general suggestions, anyone with experience might help with:

- best skylights for this purpose. I've looked at 2X4' standard, simple units for ease of replacement later.

- Ventilation. I'm looking at powered vents similar to what you would normally vent the attic with. Concerned that this may be insufficient with all of the windows

- About 1/3 (west side) of the structure will need to house equipment (mower, edger, tiller, etc) for the rest of my outdoor projects. Any specific concerns here.

Thanks in advance for any thoughts you may have. Aside from the expense, Im really looking forward to getting started. Will post updates as the project progresses.

Featured Answer

bcfromfl

14 years ago

Just a couple of impressions from scanning your post:

I'm not sure exactly where you will be getting most of your light. None through the north wall, morning sun through the east wall, and the rest through skylights? Skylights will let through some ambient light, possibly a few minutes of direct sun depending upon the pitch of the roof and the angle of the sun, but the given amount of bright light on any square footprint of gh space (for plants) would be relatively small.

Would your HOA object to twinwall polycarbonate for your roofing material? Compared with the expense of shingling and skylights, I think you'd come out way ahead, too.

If you let in more light via a twinwall polycarbonate roof, those attic vents won't be enough. You said ~400 square feet...including peak I'm going to assume a 12-foot roof space. 20 x 20 x 12 = 4800 cubic feet. Cooling and airflow is going to be your greatest concern. You're going to need heavy-duty greenhouse exhaust fans, with a combined output of at least 6000 CFM. These will most likely be noisy -- don't know if that'll be a consideration or not.

A method to reduce some solar gain is shade cloth, stretched over polycarbonate panels at a distance of about 6" or so. This is something else that might not be looked upon with favor by your HOA. It would have to be secured very tightly to make sure that one of your spring thunderstorms wouldn't carry them into the next county!

Achieving the right balance between growing plants and storage is going to be your first hurdle. What you must do right now is decide what you want to grow, and how much space dedicated to that purpose, and then design the greenhouse around that goal. Trying to make a "bright grow space" work, after the fact, almost never produces the results you're looking for. For example, if your plan was to grow plants on the south side of your garage/gh, they wouldn't get enough light because of the wall. Adequate light would only be found in the center and north side. (If this is the case, then the south side could be your pathway to access items in your storage area.)

If growing plants is not part of your plan, then forget everything I said above!

-Bruce

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Comments (6)

bangell
14 years ago
my 8x16 shed walls are built out of 6 over 9 lite "french doors"with plenty of light. Garage doors on both ends allow plenty of ventilation. My greenhouse is an 10x12 hfgh. check your salvage yards first. bangell
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My greenhouse has insulated kneewalls. Less glass needed (although the cedar tongue and groove boards were pricy!) and safer in case you bump something into the wall like the lawnmower which resides in the garden shed to the left of the greenhouse. The knee walls work without impacting light levels as all plants are either on a bench in front of the windows or on the ground at the back so get plenty of sun that angles down from above. Here's a closeup - let me know if anyone wants some details of how these are constructed.
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There is some variety in local codes related to garage conversions, so before you get too much further, see what you're up against there. If you do convert the garage are you going to want to build another one next to it or in front of it for the car? If so, another code question as to how close you can get to the lot line. To answer your question about putting in a window where the door is, all windows are really custom because they have to fit a specific opening size which isn't the same from house to house or even sometimes in the same house. So there are multiple configurations you could get, but it won't be cheap. Do something in the same style and scale as the other windows on the front of your house or else it will scream garage conversion. If you want specific advice you need to post a picture of the front of your house.
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eaglesgarden
14 years ago
I don't have a greenhouse, but I am considering one...if you are going to be making it a combo garage and greenhouse, wouldn't it make sense to make that the design all the way around?

What I mean is, don't include a lot of windows in the area that you plan to use as a garage (for storage), but increase the windows in the area that you plan to use as a greenhouse. I would also encapsulate the area used as a garage with walls (complete with insulation, for both summer and winter) to keep the heat out of the garage in the summer, and the heat in the greenhouse in the winter! This smaller greenhouse space would require a much smaller exhaust and cooling system.

Secondly, I don't understand why you would have the windows on the NORTH side. They will offer you no heating or light intake, but only be a source of heat loss in the winter. The SOUTH side will provide you with a much higher light intake, but at the same time, that will be a problem in the summer. Limiting the cubic feet of interior will limit the power exhaust fan you will need.

Personally, I am considering a combination greenhouse tool/potting shed. I don't want a lot of windows in the storage area, because that will heat up tremendously in the summer. (I don't want/need a 12 month greenhouse, just a 6 month greenhouse.) In the summer I plan to use on the tool shed, so the cooler the better! So, less windows is best there and I can use the door to ventilate as I need to go in there for items. Conversely, the greenhouse section will need to be designed to allow for maximum light in the winter and minimize heat loss at night. Insulating between the two will keep the tool shed cooler in the summer and the greenhouse warmer in the winter.

Well, I hope this helps.
cawyer
Original Author
14 years ago
First off, thanks for the input. In looking over the previous post, I mistakenly listed East and North, meaning East and South walls being "heavily windowed".

I've since obtained the approval for a 24X24 ft structure which must match "the architectural and cosmetic" appearance of our home. This will mean stucco and shingles. To the front (North) I'm planning on a garage door to the right (West) and French doors with a fancy entry to spruce up the curb appeal a bit.

In terms of utility of the GH, I'm looking to extend the growth season (veggies) and keep some year round growth. Hobby use at-most; I'm no pro. I may even build a small indoor pond for water plant growth.

Location detail: Well drained, no shade. We live on a hill with airflow that varies from heavy breeze to 40 mph winds at all times. This has proven problematic for growth outdoors due to lack of shelter but I'm planning on this helping tremendously on ventilation.

My thoughts on windows are to find the least expensive 3x6 windows for the East and South walls and place them just far enough apart to make this structurally sound. The West half of the South Wall and the West wall will have only enough glass to balance the appearance a bit. For skylights I am 100% open to suggestions. This will be applied on a composition roof. Aside from that I'd love input from you guys on #, spacing, sources, etc.

Any experience with sources for plans for the building itself? I'll be contracting the concrete and stucco. The rest is DIY.

Thanks again, J.
brandond
13 years ago
I have a 10x10 greenhouse. Im having overheating issues on these 70 plus degree sunny days. IM venting adequatly. I have a rainbarrel watering sytem setup with the guttering on my greenhouse. Its a 55 gallon barrel. Now here comes the question part. I want to use a transfer pump to irrigate my greenhouse and for cooling purposes. I bought some fancy misting nozzles, 3 are a very fine mist for watering and one is more for cooling. Would a 115 volt transfer pump do the trick. The one I have my eye on is at lowes, the water ace for 88.00 bucks. If I set it up on a timer, would it do the job. This pump will pump out 300 gallons and hr, or 5 gallons a minute. I just want something for soft misting seedlings and for watering my propagtion table. I would use pvc. I got my nozzles at AFC greenhouses.They use 1/2 in pvc. I do have a 12 volt transfer pump but I cant figure out how to use a timer with it. Its pretty much an on or off pump. Anyways IM wanting to try and make this work. Would it?
lilydude
13 years ago
Check out the link.

Here is a link that might be useful: carport to greenhouse conversion

Garage - Greenhouse Conversion

bcfromfl

Comments (6)

bangell

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Garage - Greenhouse Conversion

bcfromfl

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bangell

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