So, I have this cantilever deck that was built in 1979. The deck floor joists extend from the interior, which also holds up the floor in two rooms and the gable end structure walls off the foundation/block. I have numerous exterior floor joist portions that have rotted and need replaced. It appears these joists/boards are NOT treated lumber, and were sealed and painted with something. I think I have a good plan to replace, but I don't know what kinds of boards to use. I have access to the full length of all boards, drive in garage ceiling is not finished.
Now, wondering how to attack this.
1. If I use treated lumber, it will shrink as it dries. Since the floor joists actually holds up interior gable end walls, and interior walls, do I need to worry about using pressure treated wood and it shrinking and causing problems?
2 - If I were to use interior wood, how would one treat the interior wood to prevent rotting on the exterior?
3. KDAT lumber - should this be a consideration? Expensive, but......?
4. How would you attack this?
5. I was thinking about sistering the floor joists. Coming in with the exterior joist by 6', then using 3' on either side of the the joist's butted ends. I would add a board on both sides of the joist's mating ends, and bolt together with the use of construction adhesive. Obviously, securing back to floor, bottom plates, etc.
What say you?