my house has an exterior door that was infilled. There was a large amount of air coming in from the exterior where it was infilled, so I decided to open it up to see what the problem was. I found out that no air sealing was done which explains the draft, but I also found out that the old wood threshold and sub-sill are rotten. I can see through to the top of the foundation. See pictures here: http://imgur.com/a/wM9Aw (forum won't let me post pictures). How would you go about fixing this? I'm covering it back up, so it doesn't have to be pretty.