Our next project is a re-cover and new railings on a multi-level deck in Rochester Hills MI
When we get into tearing apart an old deck it gives us alot of good insight of deck construction failures or problem areas. One area I see alot of problems from is when two pieces of wood are sandwiched or sistered together and water can run in-between the two pieces of wood.
On this deck we are working on was a old cedar deck with a treated pine frame. To cover the treated frame they used a single 1x fascia board this typical in cedar and composite/pvc deck building, but is a sure problem area down the road. This deck is about 15 to 20 years old and it is easy to see why you do not do this. The gap between the fascia and the end grain of the deck boards created a perfect place for debris and water to build up and promote rot.
Fascia Boards: Stepped and single fascia boards where they cover the rim joist of a deck. In the picture below, we started by taking off the railings and fascia boards. If you notice the fascia board that is removed from the angled portion of this deck and you can see where we have not removed the fascia board yet. The fascia is covering the end grains of the deck boards and the treated frame. But what it is really doing is creating a space for water and debris to collect and rot away at the end grains of the deck boards and eventually the fascia.
You can see the treated pine frame is not rotted just the ends of the deck boards the fasia is rotted too. Another problem that results from this is carpenter ants and carpenter bees. They seem to feed off of the rotted area, we had to remove a couple of large nests from this deck 
This is easally prevent by running a border board around the outside of the deck or running the ends of the deck boards over the rim joist. We prefer the border board method because it hides the end grains of the deck boards. It does require more framing for the border picture frame but it is also a nice design feature. See in the picture below how this works
On this deck we have a 2 tiered fascia covering the outside rim joist. But notice the border board hides the end grain of the deck boards and covers the sandwiched or sistered 2 tiered fascia no water or debris can get into the sanwiched area From above the view of a picture frame border
Border board on a composite deck where it really sets a nice design feature
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