Mark Simmons

I am glad I finally decided to ask questions about my greenhouse project.  I would never have thought there was so much involved in insulation.  I have spent the last few days reading articles on greenbuildingadvisor.com, I found it interesting that polyiso which is rated at R6 actually performs worse that XPS which is rated at R5 in cold climates. (http://www.greenbuildingadvisor.com/blogs/dept/musings/cold-climates-r-5-foam-beats-r-6)
(http://www.greenbuildingadvisor.com/blogs/dept/musings/how-install-rigid-foam-sheathing)
(http://www.greenbuildingadvisor.com/blogs/dept/musings/calculating-minimum-thickness-rigid-foam-sheathing)

Also when placing foam insulation on the outside of your sheathing you have to make sure you use a minimum amount based on your climate zone so the sheathing will remain warm enough from interior heat to prevent condensation issues.  I had thought of placing foam board on the outside of my sheathing and another layer cut and block on the inside of my sheathing but that may cause an issue with drying condensation which likely would cause mold/rot.  From what I understand, and I may not actually understand it properly, I think I am going to use an open cell spray foam between the studs/joists with foam board on the exterior of my sheathing.  Open cell foam is much cheaper and apparently is not a vapor barrier which should allow for "drying to the interior".  All in all its much more involved than I had originally thought just for insulation never mind every thing else.

Mike I like the idea of possibly growing tropical plants year round, I recently went to an event in Holyoke MA help by Jonathan Bates and Eric Toesmeier.  Eric is the co author of Edible Forest Gardens and Perennial Vegetables. Jonathan and Eric also wrote Paradise Lot which is about their experiments in edible forest gardening on their 1/10th acre lot in Holyoke.  Anyway they have an insulated hoop house in which they are growing, among many plants, a citrus fruit which I can only describe as cherry sized lemon.   Jonathan states that his green house has never gone below 25 degrees with out any active heating.

Troy thanks for the info, I purchased that book and have started to read it.  

While researching foam board insulation I noticed a link installation instructions and also found in a question forum on a review for foam board where I learned that apparently the best place to put foam board is on the outside of our studs/joists as it keeps them from becoming thermal bridges.  I am thinking if I put a 2" foam board on the outside of my walls with a 2"foam board with radiant barrier in between my studs/joists I should get close to a R25 on the walls and greater on the roof depending on how thick of foam I use between my joists.

I had researched movable thermal insulation, mostly by mistake a few years ago.  Which is why I am planning on have a thermal blanket to attach to the underside of my glazing.

I plan on having Koi for my fish as my wife is a vegetarian and would never allow me to eat the fish I raise for my aquaponics.  They can withstand water temps in the 50s and still be fairly active.  Plus they live for a long time.

Why perennial shrubs, is this for hobby or income?

Mike
 It feels as though i have spent an eternity researching, it never even crossed my mind to call an actual insulation company.  From what I understand Styrofoam will not give me a very good Rvalue for the thicknesses they offer so think I may be better off with 3.5 inches of spray foam which should hopefully gain me an Rvalue of 24 or so not including what I will gain from the radiant barrier which appears to have a double layer of bubble wrap in its makeup, though I am sure its Rvalue is minimal every little bit helps.  As for the IBCs my fish tank is also going to be below grade, from 3 feet below grade, which is where my floor is going to be, to about 6-7 feet below grade.  This is to save space and use ground surrounding the tank as a thermal mass to help regulate the water temp.  I think the barrels stacked up in 3 rows of 9 along the north wall would save me grow space.  I agree tall plants will likely block sun and thus reduce thermal gain to the barrels but i think it unlikely i will be able to maintain big plants through out the winter, likely just cold hardy greens which are typically rather short in my experience.  For a blanket I am thinking of taping together more of the radiant blanket material and attaching it to the inside structure of my south wall.  I am thinking of using a pulley system similar to that used in window blinds to raise it up and then find a way to lock it against the wall to minimize air leaks.  Still working on that, but seeing as I am just now filling my hole in after laying in the first layer of earth tubes that is a looong way off.

Mark

Thanks Ed and Mike, I had despaired of getting any advise.  I was hoping to build 2x6 walls to gain a R value of 35+ but the cost is stupidly expensive for a backyard greenhouse, so I am going to stick with 2x4 walls with an added gap of 1" for a radiant barrier placed on the inner wall.  Plus since the radiant barrier is reflective it should bounce the sunlight around.  I like your idea of circulating water through my thermal mass barrels to maximize heat gain, though I am not looking forward to figuring out the plumbing to circulate water through 27 barrels.  I am hoping to create a thermal blanket that i can use to cover my glazing at night in the colder months and just roll up during the day.  This should hopefully reduce the BTU loss through my glazing.  I had planned on placing 2" foam insulation on the outsides of my below grade walls, would putting them on the inside be better?

Thanks

Mark

Hello all I am new to this forum and am hoping the communities collective knowledge can lead me in the correct direction.

I  have designed and hope to be building soon a passive solar greenhouse to be located in MA.  I am hoping to gain some insight as to what type/R value of insulation I need for my walls/ceiling.  My thought is to use closed cell spray foam which is supposed to provide R7 per inch.  I have also been readying recently about Radiant Barrier insulation.  Would a combination of the two types of insulation allow for less foam insulation?  The greenhouse itself will be 12' x 24' and the lower 3 feet will be below grade.  From 3 feet to 8 feet below grade will be my fish tank and earth tubes.  My back wall will have a recessed area for (27) 55 gallon drums of water for thermal mass.  For the glazing I am hoping to get triple wall polycarbonate.  I do not know what kind of temperature I can maintain with out any added heat source but I am hoping to at least keep tomatoes alive.  Any recommendations/advise would be greatly appreciated.

Thanks

Mark