Underslab Plumbing Advice for Selling and Buying a Home

Home / Underslab Plumbing Advice for Selling and Buying a Home


There is a lot to consider when buying or selling a home. And there is a lot of bad advice out there for both.

While I can’t speak to everything involved in the sale of a home, I can make recommendations when it comes to the plumbing systems for both buyers and sellers.

The Different Perspectives of a Buyer and a Seller

Before I get into what buyers and sellers should do, I want to quickly explain a theory I came up with to make selling and buying a home better for all parties involved.

Anyone who is selling a home wants to get out of the sale doing and spending as little as possible. The goal is to do nothing more than what is absolutely necessary, preferably nothing. Then when that seller goes to buy a new home, as the buyer, they want the seller to do everything.

So the seller wants to do nothing and the buyer wants to do nothing. But it’s rare that either one of those scenarios plays out whether the seller and the buyer are the same person.

It is my belief that if everyone approaches the sale of a house from the buyer’s perspective — which the seller themselves might soon be or already is — theoretically everything works out better for everyone in the long run.

I would love to see this shift in seller mindsets. If everything is paid for on the seller’s side, it will be a better situation for everyone as well as all the houses that are bought will be in better shape.

Underslab Plumbing from the Buyer’s Perspective

OK since we don’t live in that ideal world just yet, this is what I recommend for buyers when it comes to the underslab plumbing of a house they are looking to purchase.

Cast Iron Underslab Sewer Systems

For any homes in the Dallas/Fort Worth area built before 1985, it’s likely the sewer pipes are made of cast iron. While it’s possible some homes built around that time have PVC pipes, most were built with cast iron sewer pipes.

As I’ve talked about before on the blog, cast iron pipes were designed to last, at most, 50 years. Since many of the cast iron systems around today are at least 35 years old, it’s likely the pipes will need to be replaced soon, if not immediately.

Because of this, if you are looking to buy a house with a cast iron sewer system, I don’t recommend a sewer leak test. It’s a waste of money at this point, in my opinion.

In fact, not only do I not recommend a test with cast iron sewer pipes but we have changed our policy and will no longer perform these test on cast iron at all. It is such a waste of time and money, we will no longer do any repairs on cast iron, only replace.

With this in mind, I recommend you get an estimate to replace all of the pipes. And you should be able to get a free estimate. (We do free estimates for cast iron replacements.)

If you’re planning on buying a home with a cast iron sewer system under the slab, be prepared to replace that whole system. This is not a question of if, it’s a question of when. So either have the seller replace the system before you buy it, or get the money from the seller to do it.

And if you plan on getting the money from the seller to replace it after you buy it, I recommend getting a significant amount more than the estimate. For example, if the estimate is for $20,000, try and get $30,000.

As the buyer, you are assuming all of the risk and responsibility for the work after the house is sold. So if you don’t get enough from the seller, the additional cost comes out of your pocket.

One quick note, even though I don’t recommend a test in this case, it’s possible you may need to get one to justify this to the seller.

But, I repeat, never buy a house with a cast iron system without preparing for a replacement.

An Example

Several years ago, we worked with a seller in a situation that influenced why I give the advice I give today re: cast iron sewer pipes.

By the time we started working with the seller, there was already a contract on the house. After a leak isolation test, we found five leaks. The estimate to repair the leaks was $7,000 and to replace the system $12,000. (You can read this blog post to see why we no longer do repairs on cast iron systems with three or more leaks.)

The seller being the seller, had no interest in spending the money to replace the system despite our recommendation to do so and opted for the repairs instead. But once we got under the slab to make the repairs, we found there were actually 10 leaks, not five. And after giving the seller multiple discounts, we ended up doing a $15,000 job for $10,000.

But that’s not the end of the story. Because of our one year warranty, the buyer called us about a year later saying the insurance company came out and found 10 more leaks in the system.

We compared that information with ours from the previous year. There were five new leak areas and five that were in the same areas we made repairs earlier.

As I’ve explained in previous posts, when you attach a piece of PVC pipe to cast iron, the deteriorating nature of the cast iron means you will soon end up with two leaks — the spots on each side where the PVC was attached.

While we did get the system to where it wasn’t leaking after the repairs, we had to piece it together. We did what the seller wanted. But the bottom line is the pipe was bad to begin with. And because of that, we recommended to the buyer to replace the system as we did with the seller.

Pay Now or Pay Later

However, by this time, we were in the middle of raising our prices. We hadn’t changed our pricing in a long time so it was a steeper increase than it would have been had we been making incremental changes throughout the years — another very important lesson we learned from this job.

So the $12,000 replacement estimate was now $17,000.

“Technically” the seller did what was required of him, fix the leaks. But he also did a horrible disservice to the buyer and would no doubt not want the same done to him. What could have been $12,000 and taken care of a year before was now $17,000.

And we did a horrible disservice to both the seller and buyer. We should have refused to do the repairs and insist the seller replace the system. And if the seller was determined to only make the repairs, we should have walked away from the job and let him use a different plumbing company.

PVC Underslab Sewer Systems

Always, always, always insist on a test if it’s a PVC system no matter how old the house or the pipes.

We’ve seen houses with zero leaks and houses with 15 leaks in the PVC pipes. We’ve even tested a seven-month-old house and found three leaks.

Now, you might get some resistance from the seller and the seller’s agent. There is a lot of misinformation floating around that hydrostatic testing damages pipes. It does not. It only finds problems if there is a problem. The test itself does not cause damage. In fact, we have an entire blog post about it here.

You must verify the underslab situation, whether it’s cast iron or PVC, BEFORE you buy the house. Don’t just hold your breath and hope everything is OK.

Never Assume with Cast Iron OR PVC

We recently gave an $80,000 estimate to replace a cast iron system. That’s not common but it does happen. We’ve also given estimates for anywhere from $5,500 to $15,000 and $42,000.

What I’m getting at here is don’t try to guess what the cost will be because you did it before or know someone who did it on a house before. This is a common mistake with house flippers.

Every house is different. There are potential obstacles, where the system exits the house is a factor as is where the plumbing is inside of the house. There are so many different scenarios, you have to look at each house on a case-by-case basis. Make sure you know what you’re dealing with rather than going with or accepting a “guesstimate.”

So buyers, get tests and estimates. Finding out a house needs thousands of dollars in repairs after purchase can send someone into bankruptcy and foreclosure. And not only are there the cost of repairs but also the potential for damage to the house’s foundation because of the the leaks.

The cost of a test or a no charge estimate could save you from bankruptcy.

Underslab Plumbing from the Seller’s Perspective

As the seller, you are only responsible for fixing what is leaking at the time — and most sellers usually believe that’s all that’s necessary. But I suggest (again) that you approach this from the buyer’s perspective, or at the very least, consider the buyer.

Take the example from above. What I should have done — and recommend doing now in situations like this — is to get the buyer involved.

The seller from the example insisted on only spending the $7,000 on repairs and not the $12,000 to replace. So instead of wasting $7,000+ on repairs that will soon need to be repaired again — remember one leak on a cast iron system repaired will soon be two leaks — at this point, let the buyer know the situation. Give the buyer the opportunity to pay the additional $5,000 to get the entire system replaced.

Best case scenario, have the system replaced. But if you refuse to do that, DO NOT waste money on spot repairs for a cast iron system. I cannot stress this enough. Any money you spend on repairing cast iron is a waste. Give the buyer some money toward the replacement.

One, you won’t be causing more trouble for the buyer down the road. (Imagine this had been the case for you when you bought the house.)

And two, the buyer gets the replacement at the current prices. Any company you deal with could raise their prices like we did. So it’s better for everyone to pay the current rate rather than chance it a year or two down the road since you know it needs to be done soon anyway.

Fresh Water and Above Slab Plumbing Issues

Fresh water leaks are very rare. If there are any fresh water leaks, you’re looking at a couple thousand dollars at most.

And above slab problems like a leaky faucet or a running toilet aren’t going to break the bank. These typically run a few hundred dollars max.

Sellers consider going ahead and fixing these issues. And buyers if you can, get a seller to cover these but otherwise, it’s highly unlikely finding out about these later will break you financially.

Pressure Reducing Valves and Sewer Camera Testing

I don’t recommend having a pressure reducing valve installed if there isn’t one already. I explain why these valves aren’t necessary in most cases in this post.

So if you’re the seller, see if you can get by without having to pay for it or just give the buyer the money for it. Don’t go through the hassle of having it installed yourself.

If you’re the buyer, I recommend getting the money for the cost of having one installed, about $1,000 to $1,500. Put that money away or be prepared to give that amount to a buyer if you sell the house later if they insist on having one installed.

Some plumbers recommend getting a sewer camera inspection. I do not. I’ve gone in depth about what sewer cameras can and can’t find on the blog here and here.

Sewer cameras are to find stoppage hazards. (They cannot find leaks.) And it’s very rare to buy a home and suddenly discover a stoppage issue. It’s not a bad idea to get a sewer camera inspection but it’s not necessary in my opinion.

A home inspector is going to try and backup the system during the inspection by running all the water in the house and flushing the toilets with a lot of toilet paper. And if that doesn’t cause it to back up, there’s probably no issue. (You can also do this yourself.)

If you can do both a sewer camera inspection and a leak test, that’s fine. But if you can only do one, go for the leak test.

Questions? Concerns?

I strongly believe if every seller approached selling their home from the buyer’s perspective, it would work out better for everyone. Even if a seller isn’t buying a new home, if they bought the house with everything taken care of, they still end up in a better situation and are only repairing the damage that was incurred from their own time in the house.

However, until that happens, if you’re in the process of selling or buying a home now, you should have a better understanding of what is and isn’t important when it comes to the house’s plumbing.

If you have any questions or need a test or an estimate, feel free to give us a call at 972-494-1750. You can also email us at service@inhouseplumbingcompany.com.

In-House Plumbing Company

Get Sensible Solutions Today

Say goodbye to water or sewer leak issues, especially ones under your foundation, by putting our plumbing company to work for you. We offer timely, sensible solutions and restore peace of mind without significantly affecting your property or budget. Contact In-House Plumbing Company today to schedule an appointment.