I just did a house and used the "H" channel to cover the seam however it needs to be put in at the time of installation. The plastic strip is shaped like an H if you view it from the end. so when installed it covers the seam and makes the panels line up. Call Hardie. There may be a "T" channel that can be installed after the fact but there still needs to be room in between the panels to insert it.I installed using screws in case I needed to remove the panels. I counter sunk each screw and covered in with a small dab of caulking.