When re-roofing your home there is always the chance that you may need to replace wood on the deck surface (ie: sheathing). If you have an older home then you probably have plank board. Otherwise, you will be looking at plywood as the decking surface or sheathing. Whether due to water leaks, delamination or from an impact, that damaged section will need to be replaced. This is the number 1 reason why “roof overs” are not a good idea. Why put a band aid over a weakness in the top of your home? Sure, save money now but pay for it ten fold later. Regardless of the type, you have choices as to what you can use as the replacement. Most homes built in the 80’s have 3/8″ plywood. This choice is thin and has little tensile strength. OSB is particle board with little to no tensile strength and if saturated by water for any extended time virtually turns to mush. The best choice over all is 4 ply to 5 ply 1/2″ plywood. These two choices have a very high tolerance to impact, do not bow or sag in between rafters that are wider than 16″ on center. If a home has 3/8″ plywood and a few pieces are replaced with 1/2″, the difference in thickness will not be seen once the underlayment and shingles are installed. When looking for a roofer to re-roof your home, choose a factory certified roofing contractor and make sure you are receiving the best choice of materials for wood replacement.