What is the difference between kiln dried redwood versus other redwood for decking
My question is whether it is wise to use kiln dried redwood versus other grades of redwood for the deck flooring in a area that is exposed to a lot of fog and rain.
This is an interesting question. Kiln dried lumber is intentionally dried and the moisture content removed as low as possible. The usual moisture content for redwood and other softwoods at the time they are milled is usually 15% to as much as 25%.
So when wood is that wet it has expanded and will shrink gradually once placed in the field where it will remain. A deck board that starts out at 25% moisture content will very soon reach equilibrium with the ambient moisture of the air. That means it would settle somewhere around 12%-15% on average.
Kiln dried lumber is usually no more than 8%-10% m.c. This is very dry. And lumber that is kiln dried is best suited for indoor uses such as paneling where it can be installed tightly and will not move much.
Kiln Dried Redwood As Decking
Be sure to pre-drill the deck boards before screwing them to the joists as the wood will be more prone to cracking particularly at the ends. Also, if you live in a wet area you should plan expansion of the boards as they get wet.
You should not place them any closer than 3/16". Doing so runs the risk of the boards expanding and squeezing into each other if rain were sufficient to really soak the boards.
Other than that, kiln dried or non kiln dried redwood will perform well as decking.