Renovating for ROI: Plumbing Systems

DWV systems

DWV stands for drain, waste, and vent, the system of piping that carries wastewater and sewer gases out of the house. This section will briefly outline the common types of waste lines and their typical issues, but the guiding philosophy is simple: if it ain’t broke, don’t fix it. Different eras of construction used different materials, and every one of them has its own set of quirks and means of failure. Your job is to recognize what’s installed, identify any problems, and design repairs early in the process to avoid hassle later.

Clay tile: Clay tile sewer lines were common in homes built before the 1970s, and while many are still functioning today, they come with predictable issues that you should assume are present until proven otherwise. Clay is durable as a material, but the joints between sections are the weak point. Over time, those joints shift, separate, or degrade, and they become natural entry points for tree roots. Roots don’t just clog the line, they break the joints further as they grow. Clay pipes also tend to develop bellies, sections that sag and hold wastewater, because the soil settles unevenly around them. Those bellies collect debris and grease, slow the flow, and eventually lead to backups. Cracks, missing sections, and full collapses are all common failure modes as the pipe ages. If you’re dealing with a house that still has a clay sewer line, plan on a sewer scope. If the inspection shows moderate root intrusion or joint failure, replacement is usually the only good long term solution. Clay sewer lines aren’t automatically deal breakers, but they’re rarely trouble free, and you should budget accordingly.

Cast iron: Cast iron waste lines were the standard for decades because they’re strong, quiet, and resistant to intrusion, but age eventually catches up with them, and the way they fail is different from clay. Cast iron corrodes from the inside out. As it rusts, the interior becomes rough and scaly, which slows the flow and traps debris. This buildup eventually narrows the pipe to the point where even normal household waste can cause backups. Corrosion also creates thin spots that turn into cracks, leaks, or full collapses, often starting at the bottom of the pipe where moisture and waste sit the longest. Horizontal sections are more prone to splitting and failure. Once the pipe is heavily compromised, replacement is the best solution. Cast iron doesn’t always need immediate replacement, but if it’s original to the house and shows moderate degradation, you should assume it’s near the end of its lifespan and budget for partial or full replacements. Higher value markets will naturally have higher standards for what is acceptable, whereas older home markets may be more forgiving.

Copper waste lines: Copper waste lines can fail in several predictable ways. The biggest concern is with rolled copper and seam splitting. Many mid century rolled copper drains were made from flat sheet that was formed and welded into a tube, leaving a longitudinal seam that corrodes and fatigues faster than the rest of the pipe. Over time, internal acids, external oxidation, and thermal expansion concentrate stress along that seam, eventually causing long, straight cracks and slow leaks. Even rigid copper waste lines, which don’t have a seam, can develop pinhole leaks from internal pitting corrosion, especially where water chemistry is aggressive or where pipes stay wet. Once copper drain lines start failing, they tend to continue failing. For most renovations, discovering seam splits, pinholes, or widespread pitting is a strong signal that the entire copper waste system is nearing end of life and should be replaced rather than patched.

ABS waste lines: ABS waste lines are generally reliable, but there are known issues of failure in certain batches manufactured in the late 1980s and early 1990s. Several companies produced defective ABS during that period, pipes that became brittle, warped, or cracked prematurely due to resin and manufacturing problems. These failures often show up as long, clean fractures, usually at the hubs or along the length of the pipe, and sometimes entire sections bow or deform. Even outside those defective batches, ABS can develop problems from poor installation. Common issues to encounter include improperly supported runs that sag and create low spots, and solvent weld joints failing when installers use the wrong cement or don’t fully seat the pipe.

PVC waste lines: PVC is the go to choice because it’s easy to work with, resistant to corrosion, widely available, and has predictable long term performance. For most houses, it’s the best balance of cost and reliability. The problems with PVC tend to stem from installation rather than the material itself. Poorly glued joints, like using the wrong cement, skipping primer, or failing to fully seat the pipe, are the most common failure points and can leak years after installation. PVC can also sag if long horizontal runs are not properly supported, creating bellies that trap water and waste, eventually stressing the joints. Temperature is another factor. PVC becomes brittle in extreme cold, making it more prone to cracking if it’s struck or stressed.

What to inspect with the DWV system:

• Leaks: If it hasn’t become obvious, the single most important thing to check for is leaks. Any leak is a problem and requires repair or replacement. Run all the fixtures while inspecting the pipes with a flashlight, paying close attention to joints.

• Venting: While running all the fixtures, pay attention to any bubbling, gurgling, or slow draining, which can indicate poor venting. Fixtures that struggle to drain often lack adequate venting. Think of it like a straw in a glass of water, if you cover the top with your finger and lift it out, the water stays trapped because air can’t flow in to equalize the pressure. DWV systems operate on the same principle, air must be able to enter and exit the system to allow wastewater to flow freely.

• Negative slope: Check for sections of pipe that are pitched backward or sagging. This is especially common with DIY ABS and PVC installations. Because these materials are easy to work with, homeowners often install them incorrectly, creating low spots or reverse pitches that trap wastewater and cause slow drains, backups, and other problems.

Water supply systems

  Water supply systems include the supply piping, shutoff valves, and the water heater. As with DWV systems, the materials used vary based on the age of the installation, and each material has its own characteristics, limitations, and common failure points. If replacement of all or part of the water supply lines is necessary, the best return on investment is achieved by using PEX piping. PEX is the current standard for new construction and remodeling because it is significantly less expensive and easier to install than copper. Installing more costly materials typically provides no added functional or resale value and can place you at a disadvantage from a cost standpoint. As with other sections, the following material reviews outline what is commonly found and the issues you should expect to encounter.

Galvanized steel water lines

  Galvanized steel water lines are typically found in older homes and are well past their intended service life. Over time, these pipes corrode from the inside, restricting water flow and reducing pressure at fixtures. Internal rust buildup can also cause water discoloration and uneven pressure throughout the house. Galvanized piping is prone to leaks, particularly at threaded joints, and failures often occur suddenly once corrosion has advanced. When galvanized steel is present, full replacement should be expected rather than spot repairs, especially when there is access to do so while performing other repairs.

Copper water lines

  Copper water lines have been widely used for decades and generally perform well when properly installed. They are durable, resistant to corrosion, and capable of lasting many years under normal conditions. However, copper is not immune to problems. Pinhole leaks can develop due to water chemistry, improper electrical grounding, or long term internal erosion, so careful inspection for active or past leaks is important. While copper piping is ideal, it is significantly more expensive than modern alternatives and is no longer the most cost effective choice for full system upgrades. Partial repairs can be made using copper, though it is often easier and more practical to transition to PEX using appropriate fittings. It is common to see copper systems partially converted to PEX where newer renovations have been completed.

Polybutylene (PB) water lines

Polybutylene water lines were commonly installed between the late 1970s and mid 1990s and are now considered a known defective material. PB piping degrades internally when exposed to oxidants in municipal water supplies, leading to brittle pipe walls and sudden failures without warning. These failures are often catastrophic and can occur even if the piping appears intact externally. Repairs are not reliable, and the presence of PB piping is a strong indicator that full replacement is necessary. Many insurance companies will not insure homes with polybutylene water lines still in service.

CPVC water lines

  CPVC water lines are a rigid plastic piping material used primarily for hot and cold water distribution. While CPVC does not corrode like metal piping, it is prone to becoming brittle over time, especially when exposed to temperature fluctuations, ultraviolet light, or mechanical stress. Cracks and failures often occur at fittings rather than along straight pipe runs. Repairs must be done carefully, as excessive force can cause additional damage. CPVC is generally considered a functional but less forgiving system compared to newer flexible piping options. When CPVC is present, inspect carefully for leaks.

PEX water lines

PEX water lines are the modern standard for residential water supply systems and are widely used in new construction and remodeling. PEX is flexible, resistant to corrosion, and less prone to freeze related failures than rigid piping materials. Its flexibility allows for fewer fittings, which reduces the number of potential leak points. PEX systems are faster to install and more cost effective than copper, making them the preferred choice for full system replacements. When properly installed and protected from prolonged UV exposure, PEX provides a durable, long term solution for residential water supply systems. There are several types of PEX and connection methods in common use, and understanding the differences is important. PEX-A is the most flexible and is typically installed using an expansion fitting system. This method allows the tubing to expand and shrink back over the fitting, creating a very secure connection with minimal flow restriction and an excellent long term reliability record. PEX-B is stiffer and most often installed using copper crimp rings or stainless steel cinch clamps. These systems perform well when installed correctly, but improper crimping, poor tool calibration, or inconsistent clamp placement can lead to leaks. Early plastic crimp fittings and some low quality fittings have also proven problematic and should be viewed with caution. Overall, expansion type PEX systems and high quality crimp or cinch installations using brass or approved polymer fittings have shown the best performance. Most PEX failures are installation related rather than material failures, making proper technique, approved components, and quality control critical to long term reliability.

Shut off valves

  Anytime you are working with older water supply systems, you can expect to find at least a couple of defective shutoff valves. Valves may be seized, partially closed, leaking at the stem, or completely nonfunctional due to internal corrosion and mineral buildup. Older gate-style valves are especially prone to failure and often do not fully stop the flow of water even when closed. Defective shutoff valves should be replaced when upgrading or replacing plumbing fixtures. 

How to Inspect Water Lines

• Inspect any transitions between different materials, as these are common failure points. Trace the visible water lines from the point of entry through the distribution system, paying close attention to exposed piping in basements and crawlspaces. Look for active leaks, oftentimes you will see mineral buildup where there has been a slow leak..

• Check for adequate water pressure and consistent flow at multiple fixtures. Low pressure or uneven flow can suggest internal pipe deterioration, restrictions, or partially failed shutoff valves.

• Inspect shutoff valves at fixtures and at the main supply. Verify that valves turn smoothly and fully stop the flow of water. Any valve that is seized, leaking, or ineffective should be considered defective. Pay close attention to older valve styles, which frequently fail even if they appear intact.

Hot Water Tanks

Hot water tanks, also referred to as water heaters, are a critical component of the water supply system and have a limited service life. Most conventional tank‑style water heaters last approximately 8 to 12 years, although older units installed before 2004 sometimes lasted 15–20 years or more. One reason for this difference is that modern water heaters were redesigned to meet federal energy efficiency standards implemented in 2004. These standards required improved thermal efficiency, which manufacturers often achieved by adding insulation and, in many cases, slightly reducing the thickness of the steel tank walls and glass lining. While the thinner walls help reduce heat loss and improve energy efficiency, they can also contribute to a shorter overall lifespan, particularly in areas with corrosive or hard water. Regular maintenance, such as flushing the tank and replacing the sacrificial anode rod, can extend the life of any water heater, but once corrosion begins at the tank walls, replacement is typically the most reliable solution.

Because hot water tanks are relatively inexpensive, it is often worthwhile to replace an older unit before it fails, especially for the sake of marketability. For example, on a recent project, I was able to purchase a tank for around $500 with a bulk-order discount. In my jurisdiction, no expansion tank is required for private water systems, and the plumber installed it while completing other water line work. A capable homeowner could even handle the installation themselves, limiting the cost to materials alone. Anytime you can add a functional improvement with clear market appeal for under $1,000, it is usually a good value play. Appraisers generally give some credit for a new water heater compared with an older unit showing visible wear, deterioration, or deficiencies. If your tank is over 25 years old, it is wise to plan for replacement. While it is always acceptable to retain a functional unit regardless of age, a hot water tank is one category where proactively replacing an older but still working unit is rarely a waste of money. You can always leave the older functional unit and wait for a buyer to ask for it to be replaced as a concession, since this can be done at any time without affecting other projects or finishes.

How to Inspect hot water tanks:

• During inspection, check the tank for active leaks, corrosion, rust staining, or moisture at the base, all of which can indicate imminent failure. Check for leaks around the water lines. These leaks can occur at the connections where the cold water inlet and hot water outlet join the tank, often due to loose fittings, deteriorated gaskets, or corrosion at the threaded connections. Even minor drips can lead to water damage and accelerated corrosion of the tank itself if left unaddressed.

• Check the ground around TPR valve discharge. A leaking TPR valve should never be ignored, because it’s a safety device designed to prevent catastrophic tank failure. First, confirm the water temperature and system pressure are within safe limits. If they are, the valve itself is likely defective and should be replaced. Persistent leaks can also indicate a water heater approaching the end of its service life.

• Evaluate the venting and fuel source if the unit is gas-fired, confirming that vent connectors are properly secured, sloped correctly, and free of corrosion or backdrafting. For electric units, inspect the electrical connections, disconnect, and any visible wiring for signs of overheating or improper installation. Expansion tanks, when required, should be securely mounted and free of leaks or corrosion.