Water Under Floor? Here’s Why

As a general rule of thumb, moisture under your floor is, you know, a bad thing. It’s a sign that something, somewhere went very, very wrong. And it’s also a sign that you’re likely going to have some spendy repairs coming in the near future. If you have water under your floor, there are a few things to check as a potential source. Once you’ve located the source of the moisture, it’s time to call a professional.

The most common causes of water under your floor are ceiling leaks, plumbing leaks, underfloor heating, excess groundwater (or rising water), and moisture coming in through doors or windows.

That’s a lot to check with very little information, so let’s break it down a bit further, shall we?

Causes of Water Under Floor

Now there are quite a few potential sources of the issue. If you’ve experienced flooding recently, you can skip over all of this, as you likely already know where it came from. Your next most important task is to get ahold of a professional to help fix the issue. Now, onto likely causes.

Plumbing Leaks

If you’re certain that the water is coming from beneath your floor, the most likely source (aside from underfloor heating) is your plumbing. This can be made abundantly clear if the water is a) dirty and filled with waste (worst case) or b) hot.

The best way to check this is to turn off all of your water sources. Next, move to your water meter and record what it’s reading. Take a break for a few hours, and come back to the water meter (after at least 3 hours). Check your water meter and compare its reading to the one you recorded. If it’s changed, you have a water leak. If not, it’s something else.

Ceiling Leaks

This is especially likely if you’ve noticed water pooling on your floor. If there’s not water above the floor, it’s likely that this isn’t the cause. This is especially common in homes that need a replacement for their roof, and in areas with high levels of rain or snow.

Begin by listening – do you hear a dripping noise? Try to locate it. If you’re unable (or don’t hear anything), begin inspecting the ceiling near the leak for dark patches, stains, or actual moisture dripping (if it’s really bad).

You can use a wet vacuum or mop to soak up any water once you find the leak and place a pot or bucket beneath it to catch drips. Unfortunately, though, you’ll need to hire a professional to get it fixed. It’s dangerous to get on the roof, but especially so if it’s water damaged. Don’t take that risk, and instead hire a professional to get your home back in good order.

Leaking Underfloor Heating

If you don’t have underfloor heating, you can skip this section. If you do have underfloor heating, though, you’ll need to play detective for a bit. Begin by inspecting your water meter as you did for the plumbing leak section.

Once you’ve done that, your only surefire way to pinpoint a leak is to hire an in-floor heating specialist to take a look. They’ll likely use infrared thermal cameras to locate the leak (as it’s likely from a pipe sandwiched between concrete slabs). While you can buy your own equipment to do this, it will only get you so far. And the best part? It’ll cost you the same as if you just paid the plumber to do it. And even then, you still need to fix the issue, which is definitely a job for professionals, rather than amateurs.

Excess Groundwater

This will be made abundantly clear as the source of the issue if you have a basement. If you find water on or under the floor of your basement, it’s likely one of two things – first, groundwater or the water table is rising. The second likelihood is that a window to your basement is allowing moisture in – but we’ll get to that.

Unless your basement is properly waterproofed, it’s very likely that rising groundwater (caused by hydrostatic pressure) is the source of your moisture issue. The best bet to pinpoint this as the issue is to check your sump pump. This is specifically designed to move water away from your home, but over age they can fail and burn out. It’s especially likely that it needs replacement if you haven’t replaced it within the past decade, as you’re supposed to.

To mitigate the issue, you can install a drainage system in your basement floor, like weeping tiles, but that’s less than ideal. This drainage system will, well, drain water away from your home. The issue lies in the fact that it’s still getting into your home. It’s highly recommended that you locate the source of the issue and call a professional to resolve it as soon as possible.

Windows and Doors

This is the most likely source of minor leaks. If a window or door isn’t properly sealed, they run the risk of allowing moisture to seep in. This is especially common in basements, where the windows are poorly installed along ground level. Your windows should be sealed and installed at an angle to discourage water from making its way in, but that’s not always how things work out.

Your first, fastest solution should be to dry up the moisture and seal the window or door with caulk. You’ll also want a fan and dehumidifier to prevent additional moisture buildup. Worst case, you’ll need to call a professional to fix the water damage and replace your windows, though that’s not exactly ideal. Windows are expensive to install!

How to Minimise Water Damage

This is especially important if you’ve recently experienced flooding. Mould and mildew can begin to grow in as little as 24 hours, so speed is of the essence. Begin by calling a professional and getting them booked to come to take a look and try to resolve the issue. Once that’s done, you should:

  • Use a wet vacuum or mop to soak up any pooling water, and place buckets beneath clear leaks.
  • Move wet furniture out of the area, leaving it out to dry if there’s no rain.
  • Turn on fans and (if you have one) a dehumidifier in the worst room(s).
  • If you can, pull up wet carpet or flooring, especially if a professional will take a while to make it out to you. Removing a place for moisture to sit will reduce the likelihood of mould and mildew drastically.
  • Open your windows to allow a breeze – assuming again that there’s no rain or high humidity outside.

Final Thoughts

Water under your floor can come from a number of places. Whether that means it’s actually under your floor or has just made its way beneath your flooring, it’s a bad time. Begin by trying to locate the source of the leak. Check your windows and doors, ceiling, basement, and water meter. Once you’ve located the source of the leak, you need to act fast.

Do your best to minimalist moisture by cleaning up wet spots, starting a dehumidifier and fans, and sealing windows that are leaking. Once you’ve done that, you can contact a professional to take a look and try to resolve the issue. More likely than not, you’re going to need to replace parts of your flooring, plumbing, and/or windows, depending on where the leak is coming from. If the professional is a way out (weeks out), remove the parts of your flooring that are harbouring moisture. This will prevent mould and mildew from appearing any more than they may already be.

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About the Author Harry Thompson

Involved in home renovations throughout his life, Harry is an expert in everything to do with home and garden DIY. In his spare time, he enjoys cooking and tending to his garden.