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I live in Sunset climate zone 17 (San Francisco), so their were a lot of things I'd like to grow, but could not owing to the climate. My basil was scrawny, my eggplant shriveled... I was lucky to get 2 or 3 tiny tomatoes per plant. I always wanted a greenhouse but all the prefab ones that seemed large enough were beyond my price range. Then one day perusing the Harbor Freight flyer I found a 10' x 12' greenhouse for less than a thousand dollars. I spent some time googling reviews of said greenhouse and out of the box it seemed awful. One person described it as a box kite as it merrily sailed out of her garden one day ala wizard of oz. But then I found more instructions to re-enforce the structure. So late one hot August afternoon I drove north the closest HF store. I walked out with the greenhouse for less than $600.00 (using a common 20% off coupon). I choose the sunniest part of the yard with a southern exposure to site the greenhouse. From breaking ground to finished greenhouse it took about 20 man days.

Step 1: Tools and Materials Required for the Basic Construction

Tools

Skillsaw

Clamps (helpful to hold greenhouse parts during assembly)

Framing square, tape measure, level

Drill and drill bits

Power screwdriver

wrenches

vice (to flatten the emt bracing)

hand saw

Materials

10x12 greenhouse kit from harbor freight

Extreme weather foil tape (to seal the ends of all the polycarbonate panels)

12 tubes of clear Alex plus latex caulk (to glaze and seal the plastic greenhouse panels)

200 Hex Washer Head, Hex Drive, No. 10, 1 Inch Long, No. 3 Point Size, Self Drilling Screws and 200 #10 fender washers. to fasten the plastic panels to the greenhouse frame.

As needed depending on your configuration, 1/4 inch x 1.5 inch T bolts for adding interior gussets (I made mine by grinding the head down on a regular 1/4 20 tpi x 1.5 inch cap screws)

Pressure treated lumber 2 - 2x12x12', 2 - 2x12x10', 4 - 4x4x8'

1/2 x 7.5" galvanized machine bolts, nuts and washers

3" deck screws

8 sacks of concrete to set the posts

6 - 20 in. x 13 in. Gray Heavy Duty Shelf Brackets (cross bracing)

3 - 3/4"x10' steel emt tubing (cross bracing)

Optional materials

decomposed granite for flooring

Wood, screws and liner for hydroponic water culture trays.

Pump for recirculating water culture hydroponic system.

Sink and stand

Solar panels and 12 volt fan

Step 2: General Foundation and Construction Notes

For my particular installation on a hillside, I also Incorporated a retaining wall and a deck. the foundation for the greenhouse consists of pressure treated 2X12s on edge tied to the retaining wall on one side and pressure treated 4x4x8' posts set in concrete 3' in the ground on the other side to form a 10'x12' box in the ground with one 2x12 in the center running crosswise. on top of the 10'x12' box I attached pressure treated 2x6 flat-wise. on top of the 2x6 I set the steel base that comes with the greenhouse that the instructions say to "bury in the ground. I then proceeded with the very good instructions provided with the greenhouse. Until I reached the Polycarbonate panel installation part. There is an excellent instructable here for building the Harbor Freight 6x8 greenhouse, The same principles apply to the 10x12 I built.

Step 3: Polycarbonate Plastic Panel Instalation

I read a lot of reviews that talked about panels flying off and landing miles away.first I sealed the ends of all the panels with the best aluminum tape I could find I used Extreme weather aluminum tape, this prevents algae and gunk from getting in and messing up the panels. When installing the panels, I bedded all of mine in clear Alex plus caulk and used the funky clips provided to hold the panels in place until the caulking cured, then I used hex head self tapping screws with fender washers (bedded in Alex Plus caulk) to screw the panels to the aluminum cross pieces (I made 3/4 wide x 1/4 thick wood furring strips to put behind the Polycarbonate panels in some parts of the greenhouse. I have not lost a single panel so far.

Step 4: Roof Vent/windows

Save the hinge pieces that slide into the peak of the roof and throw the rest away. The windows are designed to leak. Go out and get 4 oversize pieces of 1/4" Plexiglas about 2" larger than the window/vent opening. make a 1/2" spacer out of hardwood and attach the plexi to the hinges using the spacer . I used automatic openers on the window/vents to prevent overheating (Univent Automatic Vent Opener Standard - Lifts 15 Lbs).

Step 5: Additional Bracing

I used the shelf brackets and EMT tubing to provide 3 cross braces. T bolts fasten the brackets to the greenhouse. I also used some scrap aluminum to add backing at each gable end. I used angle brackets to attach the hydroponic trays to the walls of the greenhouse, this has the added benefit of re-enforcing the greenhouse walls. The T bolts come in very handy for attaching brackets wherever you want after construction is completed. Also be sure your steel base is securely fastened to your foundation.

Step 6: Solar Powered Ventilation

Simple concept, solar panels are directly connected to fan, sun comes out fan goes on.

I added 2 sets of solar panels (shown in the first picture) directly connected to a 12 volt fan for ventilation. the fan sits over a box I framed in the floor with 2x12 that is open to the outside. I bolted 2 4x4x12' posts to the retaining wall next to the greenhouse and attached the solar panels to them.

My theory behind it is the outside air may be cooler in that low shady spot. Fan is an Endless Breeze from Amazon. Solar panels are from Harbor Freight, but with a little research you can buy better panels elsewhere.

Step 7: Hydroponics

Their is a vast number of instrutables on this site that go into a lot of detail on the subject of hydroponics. So I'm just going to touch on a few details of my system and at the middle of the page a few details that don't get mentioned enough.

The hydroponic system is a recirculating shallow water culture system, based on airstones in the reservoir, the beds are 5.5 inches deep with a water level of about 3 inches. I used a 275 gallon IBC tote for a reservoir, the large capacity reservoir provides a buffer to a lot of hydroponic problems, PH and temperature swings for example I don't change the water during the season I just add to it and watch the PPM nutrient level, pump 620 GPM Harbor Freight, Liner EDPM pond liner 40 mil, drains between beds are 2" ABS bulkhead fittings - pipe nipples cut from 2" ABS pipe set the water level - nipples are sealed with lanocote (Lanolin) to facilitate removal and replacement, with mini towers under each between bed drain. Netpots are 3", grow media is Hydroton expanded clay. I cut the netpot holes, in the redwood tops, with a hole saw and saved the rounds to make plugs for unused holes. I use JR Peters nutrients. I've had great success with Cantaloupe, Basil, Eggplant, Tomatoes and Watercress. Seeds are started in a little bit of rockwool (available from http://mcmaster.com).

One thing I will be doing is insulating the reservoir. to keep it from getting too cold. The pump and airstones provides some heat.

Hydroponic Important points

Filter your reservoir water when you fill. I use an RV charcoal filter. I'm (Camco 40043 TastePURE Water Filter with Flexible Hose Protector from Amazon).

Watch your PH with litmus paper. This affects nutrient uptake. anything lower than 5.6 will result in lockout. Shoot for a PH of 5.7 to 6.2.

Watch your water temperature. the ideal temp is 68 F. but a range from 65 to 75 F will work, mine often runs at 64F I can get 11 ppm dissolved oxygen at that temp .

I use a simple PPM meter to measure my nutrient level. The high dissolved oxygen level in my system allows me to keep the PPM under 600. Less oxygen will require more nutrients.

Watch your dissolved oxygen. Make sure your plants get plenty of oxygen. any time water is splashing, bubbling running it's absorbing oxygen. High oxygen levels promote aerobic bacteria which protects your system from all kinds of nasty things My airstones keeps mine at 9 mg/l according to my oxygen test kit (Hach 146900 Dissolved Oxygen Test Kit)

One exception to the "needs lots of oxygen" rule is lettuce... It would probably grow in orange juice.

Step 8: After 4 Years

The polycarbonate panels have no UV protection. the walls are still clear for the most part but the roof has yellowed and will need to be replaced in 3 or 4 years. the rest of the greenhouse has been great and problem free. I don't grow anything in soil in the greenhouse anymore as I've have huge whitefly infestations in the past. I'm pretty sure the wet soil is the breeding ground for my whitefly's.

<p>Try Diatomaceous earth for soil under your tables, and predatory wasps for the whiteflies. Break the cycle.though they'll be back as they live in the region in the first place, &amp; you've provided warm lodging and a cafe, also you can use sulfur smoke to really clean up bacteria.-best of luck. Of course, check with other growers in your region what they use. In greenhouses, you need to be super aware of concentrations of poisons as you too are in an enclosed space, breathing it in. This is true of the rest of the planet, but greenhouses concentrate problems.</p>
<p>This season I using yellow sticky traps, a spray bottle full of soapy water, to wash the aphids off, and a tray of pine tar under the fan no poison in my greenhouse. </p>
<p>&quot;In greenhouses, you need to be super aware of concentrations of poisons as you too are in an enclosed space, breathing it in.&quot; ABSOLUTELY TRUE!!! I was an active member of local orchid society for quite a few years. For a while I was kinda jealous of members who had a greenhouse. However, over the years 3 different greenhouse owners died, before their time, in my opinion. I know at least one of them used a quite high end respirator when he sprayed in his greenhouse and would afterwards try to stay out of it as much as possible for a week after spraying. He still died in his early sixties. BEWARE of pesticide use in your greenhouse!</p>
<p>HF Greenhouse</p><p>I built and used identical greenhouse for many years. Mine was anchored on a concrete slab with moly bolts. The slab had formerly served as a base for an above-ground pool. Unless you reinforce and seal the panels at their edges, as you did, they will blow away. In a high wind, the air pressure inside the greenhouse increases relative to the outside pressure causing it to &quot;balloon&quot; blowing out the panels. I was able to save my greenhouse on several occasions by opening the doors during major storms equalizing the pressure. I made several &quot;flapper&quot; openings that equalized the pressure for gusts to about 30 mph. To my knowledge this greenhouse is still being used after 9 years!</p>
<p>Going on our 3rd year with this. Got mine for a little over $500 on sale with coupon. Ignore the negative reviews. There are a number of blogs that show how to make it as good as the $1500 ones. Great idea about replacing the roof vents with oversized plexi. I will look into that. The only shortcoming is winter here in western Kentucky, as the polycarbonate is not a good insulator. Thanks for the post. It's given me some new ideas.</p>

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Bio: 1979-1983 Chief Engineer On a 1927 117 foot motor yacht in the Pacific Northwest. 1984-2000 General Building Contractor, Sausalito CA. 2000-Present Sr. IT Administrator , Comcast ... More »
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