Replies

1. GBA Editor
   Martin Holladay | May 02, 2017 12:13pm | #1

   Kurt,
   The easiest question to answer is the last one:
   Q. "Will south facing single pane glass loose heat on cloudy days?"

   A. Yes, unless you limit your definition of "days" to mean "the part of the day between 10:00 am and 2:00 pm" and unless you limit your definition of "cloudy" to mean "with only a very thin layer of translucent clouds."

   Q. "What is the best glazing option for balance of heat gain/loss on cloudy days?"

   A. There is no easy answer to your question. You will need to compromise. Glass with a low U-factor (for example, triple glazing with two low-e coatings and argon gas fill) will have less heat loss on cloudy days, but most types of low-U-factor glass also have a lower SHGC. High-SHGC glass (a single layer of low-iron glass) has a high U-factor. There is no magic glass with a very high SHGC and a very low U-factor.

   For more information on this issue, see All About Glazing Options.

2. 
   kaf2303 | May 02, 2017 04:05pm | #2

   Thanks for the quick reply Martin,
   Since It will need light for the plants and heat for the fish I'm probably better off with 2 or 3 layers.
   Any suggestions for sourcing glass units in the 6'to 6-6 tall range?
   Thanks again, Kurt

3. GBA Editor
   Martin Holladay | May 02, 2017 04:12pm | #3

   Kurt,
   Back in the 1970s, we were all using IGUs sold as "patio door replacement glass" -- the size was standardized and the price was cheap -- to build passive solar homes and greenhouses. You could ask local glass suppliers if they have any low-cost units.

4. GBA Editor
   Martin Holladay | May 02, 2017 04:16pm | #4

   Kurt,
   I used to buy these IGUs in boxes of 10 -- they came in a wooden crate. I still have a few in my basement -- just went down to measure them. They are 34"x76".

   I'd say "Make me an offer," but I really don't think you want them.

5. 
   STEPHEN SHEEHY | May 02, 2017 04:20pm | #5

   Kurt: If you plan on building a greenhouse from scratch, I'd look into polycarbonate panels.

6. 
   kaf2303 | May 02, 2017 05:46pm | #6

   Thanks guys,
   I will look into those options .
   Martin how many do you have? Are they 70s vintage?location? I'm near Burlington,VT.
   Stephen what is the life cycle of the pc. Insulated panels
   Kurt

7. GBA Editor
   Martin Holladay | May 03, 2017 04:42am | #7

   Kurt,
   My IGUs aren't for sale. They've been in storage for 40 years, and you don't want them. Get something manufactured more recently -- ideally, some IGUs with a low-e coating and argon gas fill.

8. 
   STEPHEN SHEEHY | May 03, 2017 06:51am | #8

   Kurt: I don't know how long polycarbonate panels last, but they are quite a bit cheaper than insulated glass. Since they are also much lighter, building a greenhouse should be easier. I'd go visit a local commercial greenhouse and see what the pros say about polycarbonate. The panels are available in a variety of sizes and thicknesses.

9. 
   kaf2303 | May 03, 2017 07:07am | #9

   Thanks a lot for the advice Martin & Stephen.
   Best, Kurt