We're needing to replace our basement sill plate. We recently noticed a very large gap between the top of our block foundation and the sill plate. It looks like the walls are leaning backwards. This was noticed right after we had a new roof put on. Upon a thorough examination, we noticed what looks like possible termite damagein the sill plate. Our walls in our bedrooms and dorway have large cracks in them. How hard is it to have the sill plate replaced and is this something we can do or should we leave it to a professional, This has to be done because it seems as if its getting worst since we noticed it.