Dear James: I am building a large new L-shaped deck. I am not sure about how to position and attach the decking boards because of the L shape. Do you have any tips? — Greg S. Dear Greg: Fitting and attaching the decking boards is usually the easiest part of a deck building project. An L-shaped deck makes it a bit more complicated, but still doable. Locating the posts and the joists properly is particularly important for a strong, stable deck with no sagging. Once you have the posts and joists installed, protect them from rot and insect damage prior to laying the decking. Even though the lumber for the joists should be pressure-treated, the pressure treatment may not have fully penetrated the wood. This is often true with lumber made from fir. The nails or screws, which attach the deck boards, slightly split the top of the joists and …