Redoing all the plumbing in a home is certainly one of the larger, messier projects one can undertake. In the absence of a basement or crawl space, one frequently has to cut out wall sections to access the pipes. In the case of a home built on a slab you may even need to remove sections of the interior floor. So you not only have the expense of the plumbing, you have to repair the damage you did to get to the plumbing.
In terms of normal plumbing failures, the biggest problem these days tends to come from older homes outfitted with galvanized iron pipes. These pipes tend to rust out over a period of 30 or so years and develop leaks. While a pressure patch can be put on an individual leak to temporarily control it, the only true remedy is to replace the pipe.
A second problem in hard water areas is the formation of calcium deposits inside the pipe which restricts the water flow. It is very much like "hardening of the arteries" in a human. Eventually the flow is so restricted that it is impossible to get an adequate flow.
Other problems occur when a safety device (such as a pressure valve where water enters the house is regulated to keep the pressure from getting too high, or a pressure/temperature safety value on a water heater, which opens if the heater gets too hot) has not been properly installed or malfunctions.
With leaking or calcified galvanized pipes, the only real solution is to completely re-plumb the house. If you have more than two leaks in your galvanized pipes, re-plumbing is probably indicated. The reason is that once the old galvanized iron pipes start to leak, they can go quickly. I've seen old pipe that had so many holes in it, it looked like Swiss cheese.
If all that's wrong is that there is no pressure valve on the house or your water heater needs a new pressure/temperature value, you or a plumber can likely install either of these in an hour or so.
What Are the Typical Costs?
Plumbing work is generally the most expensive you're likely to find on a house. That's because you may need the services of a skilled professional. Re-plumbing entire house even where there is an unfinished basement can easily cost upwards of $10,000 or more. If it is legal in your area and you are able to DIY, you can save ninety percent or more of the project cost. Well worth getting your hands dirty in my opinion.
What Are You Likely to Recoup?
The simple, very painful answer here is nothing. The sad truth is that when it's time to sell, most buyers will expect the home to have a working plumbing system. Most will not be impressed that you spent $15,000 to re-plumb the house. They'll just expect it to be there and in good shape. There are a few buyers that will appreciate it, but they are few and far between and even they will think you spent too much money doing it. On the other hand, if you don't do it, buyers will probably subtract the cost of doing it from the price they offer.
This is one of those situations where you don't do the work in order to make money or recoup money. You do it because you have to in order to live in the home, and to eventually sell it.
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