Friday, August 22, 2008

Vents 2.0

I am disappointed with the automatic vent openers. The few that did work would only open a few inches. I was worried about cooking my plants, or even worse, the kids' remaining fish! So I set off to go build a better mouse-trap.

I'll have to warn you, I run an IT department, so I know how to program and tinker with electronics....

I wanted to completely automate the greenhouse so I didn't have to keep an eye on it. At my disposal, I had an old laptop from work. I then purchased a couple of USB temperature cards and a relay card ( Next I found some used windshield wiper motors ( and started tinkering.

I wrote a controller program that was able to monitor the temperature of the greenhouse. Based on the temps, the vents are able to open & close on their own. It's easier to watch how they work, then to explain it, so here's a link to YouTube:
Click for Video

Here are a couple of closeup pics of the vent opener:

The controller is also able to plot a history of temperatures. Here's a 24 hour snapshot.

Red=outside temp
Green=inside temp
Blue=tank water temp
Black Up Arrow=vent opening (one set opens at 73, the other at 75)
Black Down Arrow=vent closing (one set closes at 72, the other at 74)
Yellow=amount of sunlight entering

So far, I've very happy with the results. I'm thinking about using the same controller to control a hydroponics system next year. Stay tuned for future posts!



Since I want to use the greenhouse over the winter, I needed a way to retain heat. First I installed 1.5" foil-backed foam insulation on the north wall. I'll probably make some removable panels for the northern facing roof for the winter.

I also built a 650 gallon water storage tank. It has a steel and wooden frame, with a pond liner in it. I could have put in tanks, but I can get more storage per square foot. Plus I turned it into a small water garden and put a couple of fish in there.

Here are Bob and George in their new home. They are about 9" long. Their old home was a 10 gallon tank! Sadly, George went to fishy heaven a few months later.

I put in a bench on the south side which is built out of some scrap plywood. I also made some planters out of some cedar and put casters on the bottom. It allows me to roll them under the benches to get them out of the way.

Here are some peppers, broccoli, and

<<Structural | Vents 2.0 >>

Structural Modifications

The sliding doors are very sensitive and can rack easily. After a month of wrestling with them, I installed simple aluminum cross braises on each door. I drilled a hole through each horizontal brace in the door and used a piercing screw to hold the diagonal brace to each section. This made a HUGE difference and both doors now glide open.

I really wish that Harbor Freight just made a regular door instead of the sliders...I'm sure it's all about saving a couple of bucks.

The most important addition I made was adding some extra bracing. During windy days, I could see the end wall bowing in and out...especially the entrance wall since the cross bracing is really poor. I bought some standard 10' x 1/2" conduit. I cut them in half and pounded down each end to make them flat and drilled a hole in them. I bent the flat piece at about a 45 degree angle for the wall side and then sort of held it in place to figure out the angle of the rafter side. I was able to use 2 pieces total for the 4 "corners"

I was also very concerned about the snow load during the winter. If there is a heavy weight on the roof, the walls will bow out quite a bit. (I tested this by hanging off the top rafter support beam!) I built a tie-rod by taking another piece of conduit and cut it to around 7'. (I measured the distance between the bolts of the angle braces to determine the distance of the holes in the tie rod.) I pounded down the ends and bent them to about 30 degrees. I also pounded down a spot in the center of the rod and drilled a hole in it. Just by luck, the remaining piece of conduit was just long enough to attach the peak of the roof to the tie rod. This simple structural change added a lot of additional stability and made the roof extremely rigid. The tie rods are tall enough where I can easily walk under them, and also hang a bunch of plants from them. The trick is to get the angles of the rods correct!

Another note. Some conduit can be brittle. I heated the ends with a MAPP gas torch so it was about red hot and pounded it down with a lump hammer on my vice. Also the coating on the conduit can be toxic, so do it outside.

<<Glazing | Additions>>

Glazing and Finishing up

Overall, I found that the entire frame went together well. I didn't have to do any modifications to it.

Once I started to put in the glazing (plastic panels), they didn't fit great. I decided to loosen ALL the bolts in the frame so that the greenhouse could flex a bit. This worked very well. All the panels fit in very nicely. I then tightened everything back together.

A couple of months after I finished, here's the final result. I put topsoil around it and planted some grass. You'll notice that only 3 of the 4 vents are open. I've already had 2 of the openers fail from Harbor Freight and a 3rd one is barely working. Total garbage as far as I'm concerned. See my future blog for my vent fix.

I also didn't like how lose the panels were...just like most people. A few had popped up during a light windy day. I decided to put foam insulation under all the panels and screw them through the centers into the horizontal bracing. This was a VERY good investment. I bought all the foam tape (3/8" wide), piercing stainless screws and washers from cheaper than the hardware stores. I also ordered a bag of clips from Harbor. Reference mudhouse's blog on how to put the screws in.

I was lucky enough to get some patio bricks for free so I was able to line the entire floor with them...really made it nice! Also, it may help retain some heat in the winter.

<<Erecting The Frame | Structural Modifications>>

Erecting the Frame

When you first start to put this together, you'll think to yourself "I can't believe this thing will actually stand on its own". You'll see in my picures that I added the diagonal cross-bracing in as soon as the corner posts go in, regardless of what the instructions state. It will make your life a lot easier if you do! Even if you have to remove it once in awhile to put in other segments.

When you're putting in all the studs, make sure you drop in the bolts for the horizontal supports. Check mudhouse's blog for more info about that. I had to unbolt things several times to put the extra bolts in....very time consuming. I wish I read their blog before I got to this part!

One other comment: I built this in March and it was below freezing most of the time. Aluminum and bare skin is wicked cold!

I decided to put all 4 vents on the southern root (I explain why in a future post). I also built the roof strucuture in my garage, mainly because it was too cold and windy. My father helped me carry it out and put it up. In hindsight, it probably would have been easier to build it in-place and deal with the cold weather.

<<Site Prep and Foundation | Glazing and Finishing up>>

Site Prep and Foundation

First, I had to pick a site that I could get a lot of winter sun. Luckily, I have a spot near my garden that is perfect. The only problem is that I had a cross slope of about 2 feet - Nobody likes a crooked greenhouse, so I did a little digging with my tractor and leveled out a spot.
That's one day gone - anyone who lives in New England knows that there are no such things as small rocks!

Unlike some folks, I made the decision to bury the steel foundation instead of building it on top of pressure treated wood. I wanted to be able to enter the greenhouse without kicking the base plate and to be able to push a garden cart through the door. We'll find out in 20 years if the steel rotted out.
Since I wanted to try to keep as much heat as possible during the winter, I bought some 1" foundation foam and laid it directly on the dirt, then built the foundation on top of it. I then drove rebar into the ground at each corner and attached the foundation to it. I'd hate to have my greenhouse turn into a giant kite during a storm.

This past year I put in a new sidewalk and patio and had a bunch of gravel left over...perfect fill for the inside of the foundation. I filled the inside with gravel and back-filled the outside at the same time to prevent the foundation from warping or shifting. One thing I noticed when filling the foundation was that the gravel packed into the "c" shape of the foundation and helped to weigh it down better. I'm now confident no one will see this greenhouse go flying through their yard.

<<Introduction | Erecting the Frame >>


Welcome to my blog about my harbor freight 10x12 greenhouse.

I've found a few other postings on the Net about these greenhouses. As with most people, I was skeptical about the quality of these, but with a few minor modifications (and a little blood), you can build a nice quality unit. If you're looking for some really good instructions, check out mudhouse's blog at I referenced their instructions several times during my construction.

In my blog, I think I'll step through my construction process, then outline some of the modifications I made to the structure to make it stronger, then show some of the additional features that I added.

For starters, I live in Connecticut. My goal is to be able to grow something year-round, minimizing the expense of having to heat and cool this thing. I'm sure it's a pipedream, but we'll find out how well the greenhouse keeps its heat in the winter.

Site Prep and Foundation >>