Insulating Wall Between two Different Slab Elevations
I have a basement with 2 different slab elevations with 2′ differential between the two. There will be a stair with 3 risers connecting them. I am insulating the basement from the inside. We are getting ready to pour the slab next week and in preparation I have placed 4″ of EPS on top of the sub-slab stone. I am trying to decide how to best insulate the concrete wall between the 2 elevations where the stair will be. While I am planning on using 2″ of roofing polyiso for the basement walls, I am am thinking I would be better off using something with a higher compressive strength where the stair will be. I am trying to avoid XPS, I do have a 25 and a 60 PSI sheet onsite that I can use for this application. I am using GFRC without wire mesh for the slab and I want to avoid placing the concrete is a compromising position. I am thinking I should adhere the XPS to the wall between the slabs and have it extend 4″ above the top of the EPS I have already placed on the upper elevation to match the final height of the upper slab. That way the edge of the upper slab stops at the edge of the concrete wall dividing the two as opposed to extending 2″ over and resting on the wall insulation.