1 hour ago, 8_Hussars said:
Sure, it could be looked at as an "odd" and different mechanic.
IMHO, crafting cobble or concrete to upgrade blocks is close enough to crafting an iron hatch to upgrade a hatch. The mechanic of "upgrade materials need to be available in inventory" covers it sufficiently for me, YMMV.
Yes, but building materials are an obvious need for building or upgrading. Having a fully constructed door or hatch to use to "upgrade" an existing one is not. At that point, you aren't upgrading... You are replacing, which is different from other upgrades. Granted, the idea that you are upgrading from wood to steel on anything without replacing it doesn't exactly make sense but it is there for gameplay reasons. I don't see why they can't just have steel in your inventory to use to upgrade the doors or hatches like you would any other upgrade. That is why I say it is odd.