You have probably heard the expression, “I’m all thumbs today,” meaning someone cannot seem to do anything right. He or she drops things, hits the wrong keys on the computer, and has trouble buttoning a shirt. Nothing seems to work right when you are all thumbs. Rules of thumb are exactly the same thing, trouble waiting to happen.
You might hear that painting will cost you $1 per square foot of house, for example. That does not take into consideration high ceilings, substantial molding and trim work, water-based versus oil based paints, or the need to protect finished floors. Painting is a messy business. Normally, you schedule painters before the flooring people because of all the drips. But, if you have hardwood floors that do not need refinishing, your painters have to be extra careful. It adds to the cost.
Even fencing, which is normally priced on the basis of number of running feet of fence line, can hold surprises for you. If you have a lot of turns, or your lot is not level, or local restrictions require black or green powder-coated chain link instead of galvanized aluminum, the cost will go up.
All the rules of thumb have the same deficiencies. A rule of thumb should be used for initial screening purposes only. They are extremely valuable for that purpose, so you should learn the rules used in your community. If you are thinking about a house that can be purchased for $75,000 and sold for $150,000, but your rule of thumb says that repairs will cost $75,000, that house is probably a bad investment and you should not spend any additional time on it. On the other hand, if your rule of thumb says the repairs will be only $20,000, then it makes sense to invest the time for a detailed analysis.