Planning a large freestanding Greenhouse in 6b zone. Need tips for best design.

[atdees]

Planning a year around orchid oriented Greenhouse that would be kept at Intermediate to cool temp range. Looking at at least 20 x 10". I am looking for ideas about wall and roof material. Snow load of 25 lbs minimum. Heating options are either propane or electrical. Need to be prepared for the occasional power outage in the winter cold. I have had a greenhouse before in So Cal but this is a totally different environment in the desert with temps down to 0F sometimes. I would love to see other peoples setups in similar conditions.

[DirtyCoconuts]

have you driven around and seen what might be in local backyards?

I am GUESSING that in your area and with your snow load there will be a lot more lean to and house adjacent models to just add strength and reduce snow load.

if you can, scope the local free standing ones (nurseries and garden centers, maybe) and copy them.

I imagine a tall A frame facing east-west would shed the snow and grab a lot of light but it would take maximum glazed material


good luck

[atdees]

The issue around here is that most local greenhouses are not for year around use. They are mostly plastic sheeting over a frame and only used from March to Oct for vegetables. Most dont seem to want to deal with heating over the winter.

[DirtyCoconuts]

I see the challenge.

Why does it need to be free standing?

I only know about how to build a foundation and a stick frame on that. There are options there, of course, but you have to just pick a construction style and the only way to do that (effectively for your area) is to talk to neighbors etc. I cannot offer that insight.

Do you have local garden clubs or orchid societies?

Even a few emails might get you some advice.

[Fairorchids]

Be careful with dimensions. There are several reasons:

Readymade greenhouse benches are usually 8' long, and 36" or 48" wide (48" is max you can reach across from one side).

You can't get good air circulation in a tunnel, so a greenhouse 10' wide, should be no more than 12-16' long.

In a greenhouse 10' wide, you can have one bench along each side, and a 24-36" aisle in the center. Making the greenhouse a little wider doesn't help, as the extra width goes to a 2nd aisle (double aisle design is not effective, unless the greenhouse is at least 20' wide).

Consider 14' or 16' wide, by 20 or 30 feet long. I have attached a diagram, showing 4'x8' bench layouts in each of the possible dimension combinations.

[Ray]

I'm going to disagree with some of what Kim stated - air circulation is no problem with properly positioned and oriented fans.

If you can make the structure square, instead of elongated, and relatively tall, you will get better temperature stability inside.

Definitely look at multi-wall polycarbonate for the covering. The thicker and more walls, the better.

Consider rolling benches, as that will give you the best utilization of space for plants.

[Fairorchids]

Ray,

While I do not have an engineering degree, I have spent 30+ years in compressed air, vacuum & liquid hydraulics industries, with 1/2 of that time in a position as Sales Engineer (they couldn't find anybody, who know what I did).

Believe me, long and skinny does not work for good air circulation (in greenhouse or otherwise), unless you put in an excessive number of fans - and that is not energy efficient.

[Steve83]

For your climate, would a foundation or kneewall help maintain temps due to the thermal mass, especially if during a power outage?

[atdees]

Thank you all for the input. The final design will be 20 wide and 24 long with Poly carb walls. The Greenhouse contractor recommends the white/opal polycarb for the light dispersion and I like the concept. I will use Propane heat so that I can keep it above 50 degrees in the winter.

---------- Post added at 06:02 PM ---------- Previous post was at 06:00 PM ----------

Thank you for the info! I am going to 20' wide so I can have room for everything including a work area.

[estación seca]

Use the polycarbonate with as many layers as you can get. Consider also for the winter tacking a layer of heavy transparent plastic landscape sheeting inside the shell on the framing to provide a layer of air insulation. Your propane bill may surprise you. The extra cost of the extra-layer polycarbonate will probably pay for itself in one winter.

And if you keep many very large water containers under the benches the water mass will absorb heat on sunny days, releasing it at night. The rest of winter it will moderate temperature swings.