I'm exploring the possibilty of building a green house and wanted to bounce some ideas around. The size would be around thirty feet deep by twenty four feet wide with a height of twelve to fifteen feet.

The entire green house will be under high Live Oak Trees and will be more for Winter protection than having a tropical growing zone. I just need it to maintain what goes inside in the Fall till Spring. In my climate that is usually mid November through mid March.

My first question is the back wall (North wall) I really think I should just build a thick insulated, maybe spray foam, wall since very little and no direct light will come through it.

My second question is the side walls at least up to the four foot level. I feel the same way about them as the rear North wall. Very little light coming through them at that level.

The area I wish to put this has flooded once in 45 years but I feel due to more construction likely the chances may increase. Because of that I intend to pour a concrete footer and have a 1 1/2 foot concrete bottom wall.

What thoughts do you have on this?

In your mild climate you don't need insulation unless you plan to maintain a minimum above 40F. I maintain 38-40F at night because that's ideal chilling temperature for high chilling fruits. It's also good for citrus and figs. My heating bill for 1728 sq ft (32x54x16) is about $300 per winter with very high fuel prices ($14/mcf) and ave winter temps of 30/60F.

I also wish I'd have built about 12ft tall rather than 16ft. Don't know why you'd need over 12ft especially in winter. Taller just adds to your heating bill. In summer the extra height can lower plant level temperatures depending on your cooling system.

I use tropicals as annuals and would like to greenhouse them to get larger specimans. I would probably go for a 45 degree minimum.

Average winter lows in your area are 40-45F. So you'd only be heating on the colder than average nights. Heating to 45F shouldn't cost more than $100 per year if the greenhouse is decently sealed. I don't see how that justifies much investment in insulation. If you were heating to 60F it would be another matter.

Its not that clear north walls don't add much light, they actually lose light in a greenhouse. The north wall should be solid, and painted white on the inside to reflect light back onto the plants. Like your intentions for the side walls, I have solid side walls up to 3 feet in height. The reason greenhouses have high ceilings is to maintain cooling at the plant level. In my greenhouse I have three ceiling fans which blow the warm air back down during the winter months. If the top of your greenhouse is going to be poly it is nice to have air inflated double layer poly. - Good luck with your new venture. - Millet

Your biggest concern should be cooling in warm weather. You need to be able to take the sides off for 10 months of the year. Your weather is almost the same as where I live in SE Texas. You only need a greenhouse a few nights of the year!

If you insist, make one out of treated lumber and 5 year poly. Get some chain link fence tubes and bend them for roof supports. Put a storm door in one end. Some removable black cloth for the roof will also help to keep down summer heat.

I once used a black shade cloth to help lower the greenhouse temperature during the summer months, and it worked OK. I have switched to a 30% aluminium shade cloth called Aluminet, mostly on the recommendation of a commercial nurseryman using the screen name Turtleman, a member of this forum. The aluminium color reflects the sun's rays away and cools the greenhouse much better. Shade cloths are manufactured to produce various amounts of shade, depending what is being grown. The most popular is one that provides 30% shade. - Mllet