Re: Bees Are Not Building New Comb
1:1 sugar syrup is for drawing wax, 2:1 sugar syrup is for building stores. The most common cause of lack of wax drawing is lack of nectar flow. You also need the bees to be crowded enough to need to draw wax in order to store incoming nectar. You do also need warm temps and a good population of younger house bees. From all you've stated so far, I'd say primary cause is lack of nectar flows in your area. That's just a guess as I can't see your conditions in the hives and the environment from here. Also, have you checked for varroa mite populations in the hives? Starting in July, and increasing into and throughout the fall, varroa mite populations tend to increase as a percentage to the bee populations. Varroa mites will cause the bees to slow and dwindle late summer into fall, and could be part of your problem.
I've been keeping a few hives for the past 20-25 years, and no longer treatment free as I got tired of the losses.