Tune in to almost any HGTV show and you’ll see episode after episode of people flipping houses and making some serious bucks. You can make a pretty penny by taking a run-down property that no one on the market wants and turning it into someone’s dream home.

But before you sign your name on the dotted line, there are a few things in your fixer-upper home you need to check. Here are six common problem areas in old houses that could make flipping it for a profit more costly than you’d first think.

The Roof

Replacing a leaky and deteriorating roof can be one of the most expensive renovations for people who want to flip a property. Roofs usually last up to 25 years before they start to break down—if your fixing up an old home, you’ll want to check how old the roof is and when the last roof inspection was done. If you buy a home with a damaged roof, you can spend on average up to $40,000 for a new roof.

Some signs your potential fixer upper will need extensive repairs include:

Loose or missing shingles
Smooth shingles
Curled shingles
Moisture in the attic or ceiling
Cracked or rusting flashing

You’ll also want to see whether or not the current homeowner’s roof warranty will transfer to the new owners after the purchase—some people assume it automatically does but that’s not always the case.

The Plumbing

Water damage is one of the worst issues that potential homeowners can find in their prospective property since it’s hard to tell just how serious the damage actually is at first glance. If there is a significant plumbing leak, a clogged pipe and plumbing vent, or overflowing drains, there could be a much more serious issue with the home’s entire plumbing system. It could cost thousands of dollars to fully replace the faulty plumbing, leaving you in the red for the rest of the renovation.

Make sure your home inspector or plumber checks for these common plumbing issues:

Broken thermostats
Rusty pipes
Clogged sewer line
Polybutylene or polyethylene piping
Galvanized pipes
Sediment build-up

The Flooring

One of the first things home inspectors do is search for signs of wood rot and insect damage. Carpenter bees, carpenter ants, powder post beetles, and termites destroy wood, making the flooring structurally unsound and can force new homeowners to cash up for entirely new flooring if they buy before having it carefully inspected.

Prospective buyers can quickly inspect the flooring by using their feet to detect any weak, soft spots in the wood—this is a clear indication that there is internal structural damage. If there is also a moldy or musty smell coming from the flooring, this could also be a sign of wood rot. The National Institute of Certified Floorcovering Inspectors can inspect your floors before you buy to make sure there aren’t serious issues that could be dangerous in the near future.

Gas

The U.S. Environmental Protection Agency (EPA) recommends that all homes be tested for radon—a radioactive and carcinogenic gas that is difficult to detect since it’s colorless, odorless, and tasteless. Even if the home has been tested for radon in the past, it’s a good idea to do another test before you close any deal. The test results only take a couple of days to be processed and can make your entire renovation happen without having to worry about faulty gas pipes leaking noxious gas into your home.

Asbestos

Fixer-upper homes are often built before 1980—making the presence of asbestos extremely likely. Asbestos was a common home insulation material for many years until it was found to be hazardous to human health. Even old floor tiles, paint, and roofing materials were made with asbestos. Thankfully, asbestos is only harmful if it’s released into the air, so undamaged asbestos doesn’t pose a threat.

Home sellers can still sell a home if it has asbestos, but they need to fully disclose it before selling or else they run the risk of being sued. If you’re considering buying a home that has asbestos, you can remove it, but most home inspectors recommend simply containing it rather than fully removing it and risking it becoming airborne.

Electrical Wiring

Problems with a home’s electrical distribution system is the fourth most common cause of home fires. It’s important to check a house’s electrical wiring before buying a home—if there are significant safety issues it could cost upwards of $30,000 to rewire the entire home depending on the size of the house the extent of the repairs. At that point, it may be more cost-effective to keep searching for a different property.

Some common electrical concerns to have checked by a home inspector or electrician include: