I have 6" channel siding around my 20 year old home. the south side that has absolutely no shade has weathered severely in the middle portion. A lot of the wood on the south (back side) of the house shows very little weathering and I would like to replace just the bad portions. How doable is this? What would the costs be to have it contracted? One contractor told me he would only do the entire side, to make sure everything "lined up" better.