I got the basic info on the web, found the most suitable area on my site and started building. My glass was free and huge! and between that constraint and the site shape I ended up making something quite different! In using it, I have found out that a considerable amount of direct sunlight in summer comes from NORTH of the east west line!
So a typical south facing lean to greenhouse will fail to collect this light!
Perhaps you can learn from my successes and mistakes and the tools I found online while trying to explain what went right.
This explains what I did, why I did it and why it works so well.
Information has come through during this project that makes a compelling case for lean away greenhouses.
Step 1: Why Is It Lean Away?
The only thing I bought for this greenhouse was the silicone to put the glass in frames and the screws to hold the wood together. Everything else, I had on site and was determined to use. The glass was 4 ft by 6 ft, 5 sheets and my wood meant that I could do 2 large frames and one small one. The glass was so heavy that I was afraid if I leaned the big pieces, it could fall over as i worked with it. It had the unusual shape so that it lined up with the fence at the side. Once I put it on blocks to keep it off the soil, it was pretty high at the front. Lean away was the only solution.!
Step 2: I Had a Few Unusual Construction Methods.
Biggest new thing I tried was buckets in the ground for some of the posts. This is mainly to prevent termines and water from destroying them. When i am happy with placement, I can add concrete or roadbase in the buckets to keep everything steady.
Step 3: Evening Sun!
Because it leans away, the sun hits the plants over the fence rather well from the north east and northwest. Recently I did a model that suggested that less than 12 hours of sunlight per day comes from the south in summer. The CR4 engineering user "Usbport" initially thought that it was 12 hours exactly but he checked with " starry night" and found around 10 and a half hours in late June comes from the south in his city! (Nottingham). Over 7 hours comes from the northern half there!
This happens in the morning and in the evening. It is this light that is far more effectively used by a lean away greenhouse.
I Include screenshots from sollumis from about 15 June, 15th September and 15th November to show how this is especially useful in summer!
Step 4: Lean-to Versus Lean-away. Angle of the Sun, Transmission and Reflectance
This is one of the big ones! Here the lean away wins really well. Glass transmits about 96% of the light if it hits it straight on but if it hits it obliquely, more and more of the light gets reflected instead of going through!
I have taken a graph from wikipedia and heavily changed it to try to show this effect. Note that it is NOT a linear effect! This means that the lean away greenhouse is way more effective than a lean to at taking in the evening light.
Step 5: Internal Reflection!
One of the really big surprises is that the north east wall of the greenhouse gets light in the evening when the sun is coming from the north west! Some of the light bounces off the angled east wall and some the front wall and hits the north east back wall from about 5 30 pm until about 8 pm.
This is an important and unexpected bonus.
Step 6: Gutters Behind
I improvised gutters and they are behind the greenhouse. Some panels of plywood is easily removed to clean them out, etc. The water is stored in a barrel in the corner of the fences.
Step 7: Easy Door
The door presented a special problem to me because there were so many ways to do it! I really like the idea of a sliding door but I just didn't have the hardware to do it. All you need for an ordinary door is 2 hinges and the door itself. But I had a sliding shower door instead of a real door. I ended up turning it upside down, taking off the sliding rollers and attaching it to a piece of 1 by 4 (that was not long enough) with just 2 screws. through the only metal that didn't contain glass on that side. I had to add another piece of wood (an off cut with a little v shape to it to contain the bottom of the door. Then I cut perspex (plexiglass) to fit the contour of the top and screwed that on too. (makes the door that tiny bit sturdier and I got one more screw in at the far side. The final act will be to add silicone rubber where the shower door meets the 1 by 4 and that will keep it solid as heck! Solid as a rock in fact! (Maybe)
Step 8: The Latch (most Primative Ever!) But It Works.
Just 2 screws and a piece of bent wire hold the door shut. Again I had the special problem with the stupid shower door. If I drill into the glass, will it break? Anyway, this is an interim method to keep it shut until I think of something better. It actually works pretty well. One more screw or an eyehook would probably make this long lasting. It can be opened or locked from inside too/
Step 9: Extreme Growth!
Things sure move quickly in a greenhouse! Today is 22nd of june, On may 9th, I sowed the stringless runner beans. The first of them were planted out on june 12th and the last ones about 5 days ago. One was already over 4 ft tall when I transplanted it! They were where the squash seedlings are now. 22nd june. The lazy housewife beans were transplanted out yesterday.
Step 10: 7th September Update. Productive!
Just a few screenshots from a little camera movie to show how well it is growing plants. This is largely irrelevant because I do not have a "control" greenhouse that is lean to to compare it to. Bur never the less. Here it is anyway. I don't feed my tomatoes or fertilize them. They get water once or twice a day if they are lucky. Sorry the pics are so blurry
Step 11: Watering
I had intended some amazing windowfarm type continuous watering system but so far it is watering can and buckets. I have used large clay pots (these have one hole in the bottom) and I just add some soil to the bottom of them. The water has stayed for up to 4 hours. My soil has a high clay content. I think metering out the water like that will help the plants get over the highs and lows of normal watering.
Step 12: Seasons and Greenhouse Design.
I expect to use this in winter too but some people live in really harsh climates and would have to abandon their greenhouse over the winter. Note if your winter is dull and cloudy (like mine) or sunny . This matters because direct sunlight is not so important then.
Maybe wind shelter is more of a factor in some places, maybe double glazing will help some in winter but not others.
I think greenhouse design is much more of a niche thing that I had expected when I started!
Step 13: Learned and Noted and for Discussion!
First off, I never intended doing anything unusual. Most of this was 'accidental design". Windows high and unwieldly and available wood a certain size so upright was easy and lean back was the only option. Pie shaped lot so to have usable space beside it, I had to have the side of the greenhouse at an angle. But it worked! And seems to be working rather well.
On google images, there are thousands of lean to greenhouse which lose out in the summer. There are also greenhouses beside fences where you need to crouch to get into the darn thing!
Hopefully people can learn from this mistake of mine.
Hopefully we can be more openminded about greenhouse design. make something that works well for YOU not someone in a different climate or at a different latitude.
We can use sollumis to better place our greenhouses and use a lean away design if you find it works in your place.
Step 14: Credits, Thanks for Help Offered and Given, Further Questions, and Doing More!
First of all a big thank you to "Usbport" on the CR4 engineering forum for pointing out the wikipedia graph that my graph is based on. This was the first step to getting the whole thing taken seriously. I have been looking into how much direct sunlight comes from north of the east west line and there is stuff to clarify. First of all the degrees of sunlight and the amount of daylight/nighttime hours does not tally. Also, if you look at the sollumis screenshots, they have "rays" of sunlight. I presumed they are 20 minutes of sun travel but they might just as easily be 5 degrees of sun travel and they are bunched closer in the morning and evening than at midday. I am pretty sure that the sun does appear to be going faster at midday and slower in the evening. I could easily check this if I had not destroyed my model http://www.youtube.com/watch?v=R67f2v4yio4 This really matters because we need a decent idea of how much light we are gaining.
Finally a shout out for art of illusion. It is a free cross platform modeling software that is easy to learn. I firmly believe that this is the best hope to personalize the greenhouse design. The only extra thing that is needed is a Sun engine Scene file. Scene files are downloadable and anyone can make one. (I am crap at it but even I have made a scene file). http://www.artofillusion.org/contribute if you want to talk to the guy who made art of illusion. Here is how it would work. You import or copy your elevation, plan and endview into art of illusion, add the scene file. input the date and run it. It will show the light and shadows from any angle for your entire site for that day! Any decent physics or computer guy could do the scene file, it would look great on your resume and it would be used all over the world for greenhouse, and garden design.