I have a 25 year old log cabin with cathedral ceilings. I would like to add another layer of foam insulation and then cover with barn board. This will still leave exposed beams and keep the overall look the same. Any helpful ideas for this project?

Here is just an idea for you to consider. At 25 years old you may be in the market for a new roof just down the road. Eagle systems makes a insulated panel you can add to your old roof and then shingle over it. This is likely not a good DIY project but barm bopards and insulation on the inisde is way more work than you might think. I have tried it. Eagle Panel Systems: What's New