Hi. I'm rebuilding an old porch that has tongue and groove decking that has started to rot due to plastic sheets that were placed over top of them. I will be replacing the tongue and groove with new T & G yellow pine decking. The porch is bounded on three sides by brick walls and it is not a covered porch. My question is, "How much of a gap should I leave between the new decking and the brick walls to allow for expansion?" Also, I must make this new porch so that no rain leaks below it since we use the space underneath to store things. I will be soaking the ends in sealer/waterproofing prior to priming and painting with a good porch floor paint. I appreicate any tips or techniques in doing this job. Oh yeah, I do not want to use pressure treated wood. The old decking (most likely more than 60 years old) would have lasted if not for that plastic that was laid down on top of it. Also, I don't want too much buckling to occur, any suggestions on that issue too would be appreciated.