I did an in-person inspection consultation recently. A man bought a 50-year-old home next to a ski resort. He and his family are avid skiers and were tired of renting expensive condominiums. He wanted my opinion about the condition of the house and how to schedule remodeling work that might span two or three years.

Based on the plans he showed me, this tired home requires a full facelift, inside and outside.

I discovered that the radiant heating system and most of the plumbing drains and vents are installed incorrectly. It turns out the previous owner was an avid DIYer. He knew just enough about building and remodeling to be dangerous.

The first thing I noticed once I walked into the house was the 3-inch toilet drain pipe visible in between two ceiling joists above my head. This pipe had an oversized 2-inch vent pipe. A 1 1/2-inch vent would have been sufficient and code-compliant.

The DIYer had to flat-vent the drain pipe because it was in a narrow joist space. He did the right thing by rotating his fitting. This prevents toilet water from backflowing into the vent pipe. Unfortunately, he used a T fitting instead of a Y. A T fitting allows two pipes to connect to one another at a 90-degree angle; a Y fitting makes the connection at a 45-degree angle.

Using the T fitting wasn’t his most grievous error. He extended his vent pipe about 30 inches and then went down 4 inches. He was extending the pipe to a place where he could turn it up into a wall. This horizontal length of pipe is no different than the p-trap under your fixtures. My guess is that, after all these years, the horizontal pipe had filled with water, rendering the vent useless.

Vent pipes need to be sloped at all times, like drain pipes. This allows the condensation inside the pipes to drain by gravity to the sewer or septic tank.

This DIYer also made a serious mistake on all his soldered copper water lines. I could see the green remnants of the liquid flux that had flowed down over the tubing as he soldered. He didn’t clean the flux off the pipe. This excess flux can lead to corrosion. Old towels cut up into rags do a great job of removing this soft flux once the copper pipe is cool enough to touch.

You might make a serious mistake sizing water lines. Luxury showers can gulp 10 or 11 gallons of water a minute. Half-inch diameter water lines will not suffice. In some cases, three-quarter-inch-diameter water lines may not work. Keep in mind that PEX water lines often have a smaller inner diameter than copper.

The current craze of luxury vinyl plank flooring may cause a water leak in your home. You, or the flooring installer, may remove a toilet in a bathroom, allowing the LVP to be placed under the commode. If the toilet was installed with a time-tested wax ring, you automatically break the seal when you lift it up.

A secondary problem can occur because the top of the toilet flange is now flush or below the new finished surface of the LVP. Toilets are designed so that the flange should sit on top of the finished flooring. You may have to stack two wax rings on top of one another to get a water and gas-tight seal.

Teflon tape can cause you to pull out your hair. I’ve never been a big fan of it. I prefer to use gloppy thread-sealant compound brushed onto the male threads of a pipe. DIYers often don’t wrap the Teflon tape onto the threads tightly enough, or they wrap it in the wrong direction. Teflon tape needs to be wrapped in a clockwise fashion as you look at the end of the threaded end of a pipe.

Are you thinking about installing a new garden hose faucet? Most plumbers and almost all DIYers pipe hose faucets with a half-inch-diameter supply line. You’ll be astonished how much more water you get out of a garden hose by feeding the hose bib with a three-quarter-inch pipe.

If this new hose faucet is going to be inside a garage, consider installing a hot/cold hose bib: You can have all hot water, all cold or mix them for warm water. Washing dogs, cars or any other item in chilly weather is so much nicer when you have hot or warm water.