you dont need to and it doesnt effect the light.

It won't affect the light, but, in your Zone, you need as much insulating effect as possible. So something beyond single pane is prudent. Are you actually using glass, or would you consider something like twin wall or triple wall plastic? And when you say "double up" the glass, do you mean laying two panes on top of one another without an air space?

yes I am using glass which has a very thin and narrow aluminium frame and I would like to somehow be able to use two panes one on each side of 4 by 4 cedar frame. Thanks again

kavik-
Having an air space, as it sounds like you are going to do, is important. However, just be aware that you will likely get some condensation between the two panes of glass, and over time you could have mold or other microscopic plant growth between the panes and hazing up the view. For that reason, if you can figure out a way to easily de-mount one set of panes for cleaning, it might be a good thing.

Thank you kudzu9, I think I will only put one pane as I did not consider the issues you brought up.

kavik-
I didn't mean to discourage you, but I did want you to be aware of potential problems over the long term with what you were describing. In your Zone -- if you are going to try to use the greenhouse for any purpose during winter -- some improvement over single pane glazing is prudent, especially if you are providing supplementary heat. Some people use a solar pool cover as a relatively inexpensive and temporary way to provide improved insulation in winter. What are your plans for this greenhouse?

kudzu9 I plan on trying to get 2 to 3 months extra growing time to grow flowers for outside,vegetables suitable for freezing which grow well in greenhouses. I apreciate your
help since I am new at this.

Thanks Again