I'm using a farm house as my home base and am trying to upgrade the exterior doors and walls. I was able to upgrade the exterior doors. When I point the upgrade tool (nail gun in this case) at a wall, it makes this clanking sound and displays a red X and the icon for wood. I am carrying 500+ wood in my inventory, so I'm wondering if am I able to upgrade the walls?
Edit: attached screenshots showing the nail gun trying to upgrade a wall with the wood icon popup in the lower right, and the second showing 542 wood in my inventory.