Budgeting for CapEx

[Max T.]

So I've finally got around to creating a spreadsheet for CapEx budgeting and want to make sure I'm not missing anything. For each component I've estimated the cost to replace, the estimated number of months of remaining lifespan, and divided those numbers to arrive at an amount per month for each component. I've done that for all of my properties and totaled it up to show me how much I should be saving each month for that rainy day.

The components I am tracking are: roof, furnace, water heater. What am I missing? I don't have central air conditioning in any of the properties.