Please help,I need advice from greenhouse experts

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Forum topic by a1Jim posted 07-15-2013 06:07 PM 1691 views 1 time favorited 26 replies Add to Favorites Watch
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07-15-2013 06:07 PM

Topic tags/keywords: question

Hi Gang
I have posted this on garden tenders also. I was hoping I could get some advice on Green houses ,I have a customer in southern Oregon that wants a 10’ x 40 greenhouse and I’ve been doing research on line and there seems to be two schools of thought what’s best polycarbinate vs glass as to whats best and hold heat best. I also seem to be getting conflicting stories as to it’s best to use fans or automatic vents. Lastly I would like to know a good source for buying a kit that large and perhaps companies that are not desirable to purchase from.

Even though I’m a contractor with 25+ years experience I have never had a greenhouse nor am I a gardener so I really could use your help.

Thanks Jim

-- wood crafting & woodworking classes

26 replies so far

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Jim Jakosh

21501 posts in 3277 days

#1 posted 07-15-2013 06:27 PM

I’m not a greenhouse builder either, but I found this link for you:

Cheers, Jim

-- Jim Jakosh.....Practical Wood Products...........Learn something new every day!! Variety is the Spice of Life!!

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#2 posted 07-15-2013 06:29 PM

Thanks a lot Jim that looks very informative,I’ll look it over very closely .

-- wood crafting & woodworking classes

View CalgaryGeoff's profile


937 posts in 2653 days

#3 posted 07-15-2013 07:05 PM

Jim sounds like a big project. What do you think you will use glass of polycarbonate windows?

-- If you believe you can or can not do a thing, you are correct.

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117270 posts in 3748 days

#4 posted 07-15-2013 07:15 PM

It’s hard to tell at this point Geoff,that’s part of why I asked for help here .

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View MtnMystic's profile


19 posts in 3206 days

#5 posted 07-15-2013 07:15 PM

We have a greenhouse that was built before we bought our property. Some things we would recommend: Keep with a dirt floor not concrete as concrete sucks the greenhouse heat away in colder weather. Use one of the plastic woods where there is contact with the dirt to avoid rotting wood. Automatic vents with fans are important and enough are needed to actually circulate the air so there must be an adequate outside source for air to come in as well. Our greenhouse was insulated and green wall board used with plastic between the wall board and insulation but the wall board should have never been placed near the ground or concrete. Double or triple wall corrugated polycarbonate instead of glass (Tek Supply), and a door that lets in light plus a screen door so you can use it for cross ventilation. If it is used year round and heat will be needed to supplement in winter, plan for that and add lighting into the design plus lots of wall outlets. Don’t make the whole building polycarbonate, just the south wall and add a some windows to the east and west. The south wall can have a short solid wall for the first two feet but if you insulate it, use plastic wall sheeting at that lower level. Then start the polycarbonate. Another layer of corrugated Polycarbonate on the inside south wall rafters above the short wall will create an air pocket that keeps the greenhouse from getting so hot and will reduce it losing heat when it is cold. We installed a greenhouse bubble wrap (Tek Supply) to reduce loss of heat but would have rather had another layer of the polycarbonate. It was just to hard to do since it wasn’t designed for that. We use our greenhouse year round at 9,400 ft elevation. It can be above 90 degrees in the winter so venting must be a year round option. At night in winter when it is 30 degrees below zero and with high winds, the challenge is keeping it warm enough that it is above freezing. We have used some oil filled heaters to do the heating but would like to install a 220 electric heater. We have grown banana trees, tomatoes, grapes, an olive tree, pomegranate, citrus trees, a fig tree and many vegetables year round in the greenhouse with success. In fact the banana trees grew so well they got too big, so they had to go so we could have more space for other vegetables. Keep the roof a solid shingled roof as you won’t gain enough light to warrant the heat loss from the polycarbonate if it is placed up top. They made that mistake with our greenhouse. You sunlight is lower in the winter and you gain enough sunlight in the summer like a sunroom. Hope this helps.

-- MtnMystic, Colorado,

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117270 posts in 3748 days

#6 posted 07-15-2013 07:24 PM

Wow that’s great info many things I might not of thought of, Thanks Mtnmystic

-- wood crafting & woodworking classes

View Don W's profile

Don W

18988 posts in 2739 days

#7 posted 07-15-2013 07:32 PM

Jim, I built 2 green houses about 25 years ago about 200’ x 300’ each. We used Russian glass. (I don’t remember why) The structure was all glass and steel with drip tubes approximately every 6” apart. The building inspector decided we needed a sprinkler system. I had to go to the state to get a variance so we didn’t need a sprinkler system in a building were absolutely nothing was combustible.

I’m sure it doesn’t help, but just something else to think about.

-- - Collecting is an investment in the past, and the future.

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117270 posts in 3748 days

#8 posted 07-15-2013 08:35 PM

Wow those were some big greenhouses Don,sometimes those inspectors can make it tough. Thanks for your input.

-- wood crafting & woodworking classes

View Elksniffer's profile


101 posts in 3569 days

#9 posted 07-15-2013 09:16 PM

Hi Jim. I just built a greenhouse 16’ by 40’ using 2” PVC for the hoops. I purchased a ventilation package(fan, automated louvres, thermostat control) and film from Greenhouse Megastore and they were very good to deal with. Vents might be nice as primary cooling, because you won’t have to listen to a fan, but if you have very high summer temperatures I believe a fan would be necessary. I don’t think the heat holding value of glass or polycarbonate is enough to keep much heat in the greenhouse at night or winter months. Mass that can absorb heat during the day and release it at night or a heater of some sort probably would be needed depending on ambient night time temps and what temperature you want to maintain.

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117270 posts in 3748 days

#10 posted 07-15-2013 09:23 PM

Thanks for your advise Elksniffer

-- wood crafting & woodworking classes

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2689 posts in 2448 days

#11 posted 07-15-2013 10:15 PM

a1jim....I have nothing pertinent to add about greenhouse building, but am looking forward to seeing this as a project post when completed…good luck

-- Measure "at least" twice and cut once

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2328 posts in 2599 days

#12 posted 07-15-2013 11:15 PM

Hi Jim,
Our green house which is on a much smaller scale uses both auto vents and a fan, here in the Seattle area. On hot days we leave the window and door open. Pollinators need access to the plants!

Regards Vince

-- Love thy neighbour as thyself

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2822 posts in 2859 days

#13 posted 07-15-2013 11:17 PM

cant help on your quest but i can wish you all the best

-- Stelios L.A. Stavrinides: - I am not so rich to buy cheap tools, but... necessity is the mother of inventions !!!

View teejk's profile


1215 posts in 2856 days

#14 posted 07-15-2013 11:31 PM

Please keep us posted on this one. Dad always said “mow it or hoe it” and I have a spot for a small greenhouse. And when you get done with the greenhouse, let’s move the discussion to smoke houses (the old fashioned ones where a small pile of green wood smolders for days with meat hanging overhead). I have room for one of those also.

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117270 posts in 3748 days

#15 posted 07-15-2013 11:57 PM

Thanks everyone.

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