Plastic Free Timber frame addition – GreenBuildingAdvisor

My Partner and I have a 3 story brick house in Philadelphia (4A) and we’re adding a room above the single story kitchen. Demo is all done and we’re just waiting for permit amendment approval. She has a green architectural coating business (linseed oil paint and pine tar) and we’re both obsessed with greener building materials. Our goal is to avoid the use of plastics or petroleum based products when possible. We don’t think these materials are appropriate for a building we want to last 100+ years. 

The addition is going to be Timber framed out of big green red oak beams. with tongue and groove sheathing, Pine coated in linseed oil on the sides and Red oak T&G on the roof. this will also be visible in the ceiling. The roof will have exterior rockwool insulation and the walls with have 2″ of  continuous exterior rockwool board and 3.5 of R-15 batts between the studs. We’re doing a standing seam metal roof, its is fairly low slope 12/2. We will have 2″ of vent space between the metal and insulation. We think we’ll have a Layer of Ice and water between the metal stand seam and the sheathing it attaches to but we’re not sure where and if we should put a layer of something else like wax paper directly on the Oak Tongue and Groove to help with air tightness. 

attached is a cross photo section of the assembly that we’re thinking of doing. Also included a photo of the floor of the addition timber frame room that we’re so excited about!  So is there anything wrong with this or are there better green products we could use? Are we being foolish?