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Gayle,
There are as many different opinions on this subject as there are warehouses for bourbon. I personally think that the best whiskey is aged in iron clad warehouses where the extreme temperatures do take effect. But then again I am pretty damned fond of the Old Forester Signature and that whiskey is aged in heated brick warehouses. I simply look at the different styles of warehousing as another step in the final recipe for the bourbon.

Gayle,
I would say that light is not important in any way other than a source of heat. Air flow is much more important than whether the warehouse is dark or not. The ricking system was designed to increase air flow around the barrels, preventin musty whiskey by keeping the barrels dry. That is why they open windows in the summer - to increase the air flow in the warehouses.

Masonry warehouses are often heat-cycled. They don't stay at the same temperature year round. They are heated and then alllowed to cool before being heated again, to simulate a natural cycle.

People with masonry warehouses heat-cycle for two reasons. One, because they can, due to their superior insulation. Two, because they don't get as much of the natural cycling, also due to their superior insulation.

You will find most masonry warehouses in cities. They are masonry for security more than any other reason. The walls of a steel clad warehouse are just thin corrugated steel. You can break in with a pair of tin snips.

In the city, warehouses also have to be built close together and close to other buildings, due to the cost of land. In the country, they can be built on hill tops, exposed to plenty of sun, with lots of land around them so they get good air circulation.

It's no coincidence that the first use of heat cycling was at what is now Woodford Reserve which, although it is in the country, is in a river valley where it's very humid, they don't get all day sun, and the air doesn't move much. Contrast that with the Heaven Hill, Barton and Maker's Mark warehouses (the ones in Loretto, not the ones at the distillery).

Chuck,
I don't think that you can break into an iron clad warehouse with tin snips. All of the iron clad warehouses I have seen are tin over a wooden board wall. There were also a lot of iron clad warehouses in Louisville at one time. The Stitzel distilleries at 26th and Broadway and on Story Avenue had iron clad warehouses. Hill and Hill had both brick and ironclad warehouses. Yellowstone had ironclad. Glenmore in Owensboro also has ironclad.

With that said, Chuck does make some good points about brick/stone warehouses. They are a better security in the city and the theory was they would contain fire better should they catch fire. They don't reach the same extremes of temperature, but do get pretty hot in the summer. I think the type of warehouse is mostly dependent upon the distiller and their theory as to what makes their whiskey taste better.