What should we check in the basement before we buy a house?
Answered by the column’s editors · · about 5 minutes to read
For a basement inspection before buying, look at where water comes in and goes out: the sump pit, floor drains, the water heater's age, exposed pipes, signs of past water, and the permit history.
Your home inspector will look at a lot, but the basement is where a few minutes of your own attention pays off. That's where the water heater, the main shutoff, the sump pit and the lowest drains all sit, and where past trouble tends to leave marks.
Bring a flashlight, your phone's camera and a list of direct questions for the seller.
What should a sump pit look like?
If there's a pit, lift the cover and look. The model plumbing code (2012 IPC) sets a minimum pit of 18 inches across and 24 inches deep, with a solid bottom and a removable cover. Ask when the pump was last tested and whether there's a battery backup.
Then follow the discharge pipe. It should leave the house and empty outdoors, away from the foundation. A sump line tied into a drain or the sewer is a red flag: in Montgomery and Prince George's, the 2024 WSSC code names a foundation sump pump connected to the sanitary sewer as an illegal discharge. Our page on where sump water can go covers the rules.
How do you spot signs of past water?
Look low: tide lines on drywall, rust at the feet of metal shelving, a new patch of carpet, fresh paint on only the lower wall, a musty smell. Each is a question for the seller.
Seepage through walls matters for more than repairs. The Maryland Insurance Administration treats seepage through a foundation as a maintenance issue that policies generally don't cover. Drain backups are a separate story, covered in our sewer backup insurance answer.
Bring a cheap humidity meter if you can. EPA's mold guide recommends keeping indoor humidity below 60 percent, ideally 30 to 50.
Is the water heater near the end of its life?
Find the label and the serial number; the maker's site or your inspector can decode the date. The Department of Energy puts typical tank life at 10 to 15 years. A heater in that range isn't a deal breaker, but it's a cost to plan for.
While you're there, check that the relief valve's discharge pipe runs down toward the floor and isn't capped or plugged. A pan underneath is a good sign. More on water heater age here.
What about drains, the backwater valve and any bathroom?
Sniff the floor drain. A sewer smell often means a dry trap; the floor drain smell page explains the fix. If there's a backwater valve, it needs an access cover you can open, and in WSSC homes the cover should carry a label warning not to cover it with flooring.
A basement bathroom below the sewer line needs an ejector with a sealed, vented lid. Ask for permit and inspection records for the bathroom and any valve or ejector. If none exist, our page on permits for a basement bathroom explains why that matters.
Where are the main shutoff and the service pipe?
Locate the main shutoff valve and check that nothing blocks it. Look at the pipe where it comes through the wall, and at any pipes along exterior walls or in a crawlspace, which are the ones most likely to freeze.
WSSC Water's short video shows how to find where the service line enters the house and how to use a magnet and a coin to tell what the pipe is made of.
Should we test for radon down there too?
Yes. EPA's Map of Radon Zones puts Baltimore, Frederick, Howard and Montgomery counties in Zone 1, its highest-potential group, and Anne Arundel, Prince George's and Baltimore City in Zone 2. But EPA says the map shouldn't decide whether a house gets tested. Test every home, and fix at 4 pCi/L or higher.
| What to check | Good sign | Ask the seller |
|---|---|---|
| Sump pit and pump | Covered pit, discharge pipe running outdoors | When was it last tested? Any backup? |
| Walls and floor | No tide lines, rust or fresh patches | Has water ever come in, and from where? |
| Water heater | Under 10 years old, relief pipe aimed down | When was it installed, and by whom? |
| Floor drain | No sewer smell, grate clear | Has it ever backed up? |
| Basement bathroom or ejector | Sealed, vented lid; permit on file | Was it permitted and inspected? |
| Main shutoff | Easy to reach, turns by hand | When was it last used? |
Before you sign
- Open the sump pit cover and follow the discharge pipe outside.
- Photograph the water heater label and every stain or patch you see.
- Run water in the basement sink and smell the floor drain.
- Ask for permit and inspection records for any bathroom, ejector or backwater valve.
- Order a radon test, and write any repair asks into your offer.
The bottom line
Spend your basement time on the water: how it gets out (sump, drains, ejector), where it has been (stains, smells, humidity), and what holds it (the water heater). Ask for permits, test for radon, and put what you find into the negotiation.
Readers also ask
Is a sump pump a bad sign in a house we're buying?
Not by itself. It means the house manages groundwater. What matters is that the pit is covered, the pump works and the water ends up outdoors.
What if the basement bathroom has no permit?
Ask the seller why, and ask your inspector to look closely at the ejector, venting and drains.
Can a sump pit help with radon?
EPA's radon reduction guide says a sump can be capped so it still drains water and doubles as the suction point for a radon system, cutting radon by 50 to 99 percent.
How do we know if the water heater is gas or electric?
A gas heater has a gas line and a vent pipe running out of the top; an electric one has a wire connection instead. Gas work in WSSC territory is licensed-only.
Does a wet basement mean mold?
Not necessarily. EPA says mold usually won't grow if wet materials dry out within 24 to 48 hours. Our page on mold after a leak has more.
Where this answer comes from
- WSSC Water: 2024 plumbing and gas code, illegal sewer discharges (archived copy)
- Maryland Insurance Administration: flood vs. water damage (archived copy)
- EPA homeowner mold guide
- U.S. DOE Building America: Tankless Water Heaters (2009)
- U.S. EPA: The EPA Map of Radon Zones
- U.S. EPA: Consumer's Guide to Radon Reduction (2016)
- ICC model plumbing code, 2012 edition, on archive.org
