I have discovered wood root at the bottom of the laundry door door jams. It affects the bottom 100-150mm on each side. I have both a solid laundry door that opens in and a 3 point security door opening outward.
I have watched multiple YouTube videos on how to repair and fell that I know what to do but I have a few questions.
1. In Australia can I just cut out the damaged portion and replace it or do I have to replace the full verticals on both sides.
2. In undertaking this job I am concerned that the tiles have been put on after the timber. This appears to have provided the scope for the water to be trapped between the timber and tiles and therefore root. I was wondering if it would be better to tile and then insert the timber, this way the waterproofing would between the tiles and brickwork and the timber would sit above that so as not to create a pool of water.
I have provided photos of the damage below.



PS. There is no step actual outside this door, just a drop of 250-300mm to pebbles and the occasional concrete pavers used a stepping stones. I need to address this also but that is a later project.