I am in the Houston Texas area. My house was built in 1978. A roofer told me that code for rafter spacing in my area (Deer Park) is 18 oc. Some of mine are much more, like possibly 28 in a couple of places. The roof was replaced less than 10 years ago (I think), has 3/8" decking, is wavy and leaking. The roofer recommended that we remove the shingles, replace any rotting 3/8" decking (with 3/8), and then add a layer of 1/2" decking over that. He said the rafters would support it ok, and it would work. Is this a sound recommendation?