Q: I had some moisture in my basement this winter–got onto the carpet foam and made a mess. I removed some drywall to see if there was a leak, but the only obvious issue is wetness on the vapor barrier directly behind the drywall and dampness in the drywall as well (see photo). Any ideas how to deal with this?
The foundation and fiberglass insulation appear to be dry–it’s just the interior side of the vapor barrier facing the drywall that’s damp. It’s a daylight basement on one side, but the section in question is completely below ground.
A 2×4 wood wall is placed against the concrete foundation, insulated with unfaced fiberglass, then covered with a plastic sheeting vapor barrier, and then drywall.
I’m not sure if there is any waterproofing or dampproofing on the outside of the foundation. The house is up in the mountains so it gets pretty cold in the winter–usually in the teens but can be colder. I don’t think the water is near any pipes, so I assume it’s a condensation issue of some sort.
The entire basement is insulated and finished except for the mechanical room, which has the insulation and plastic wrap, but no wallboard.
The space is heated and cooled with a conventional forced-air system.
The vapor barrier material has a paper facing on the exterior side and plastic sheeting on the room side. The seams are not sealed.
The moisture problem is occurring in the winter on the side of foundation that s deep in the ground (not the daylight side). It is in just one spot, as far as I can tell. It doesn’t seem like a huge amount of water, but just enough soaking the carpet bad to make a mess.
It’s a vacation house so there are weeks where no one is there–it’s hard to say how long it took to happen. There are no pipes in that wall. But there’s a bathroom roughly above it, but not in line with where the water is coming out. No water stain on the ceiling however. There may be a pipe coming in from the well somewhere NEAR there but I’m not sure where it is. (Or what it’s made of, but I did wonder about condensation on that pipe.)
The problem seems to appear only in winter. It can get cold here — it was below 0 degrees F a few times this winter. There’s also a lot of snow (and melt) on the ground, which complicates the issue.
We’re the second owners, so I’m not sure if the foundation has footing drains. But there’s a pretty robust gutter / drainage system–the downspouts all go underground and tie into one big drain that spits out water on the far side of the property. There are gutters on the side of the house that has the issue. The foundation is only about 15 years old, though. Thanks. — Jude
A: Thank for all the details, but sad to say that nothing pops out as the obvious answer. You’ll have to do additional investigations to determine whether the source of the leak is plumbing, foundation leakage, or even wall leakage from above the foundation. Since water run downhill (and sometimes sideways along building elements) it’s often difficult to find the source.
Basement Insulation Problematic
Your basement insulation system, using a framed wall, fiberglass, and a vapor barrier, is very common, but also prone to moisture problems. The best way to insulate a basement on the interior is with extruded polystyrene (XPS) foam board against the wall, but that’s not an option for you without tearing out everything and starting over.
The most common problem with your type of wall is moisture getting trapped on the exterior side of the vapor barrier leading to wet insulation and moldy, rotten wood. This is primarily a warm-weather problem where the foundation wall is cold enough to condense moisture from the interior air. Or moisture may build up on the back (exterior) of the vapor barrier if the basement is air-conditioned and the vapor barrier cool enough to from condensation from air in the stud cavity.
However, you are getting moisture on the room (interior) side of vapor barrier in the winter. If this was occurring on the side of the basement exposed to cold, winter air, I’d suspect that the vapor barrier was cold enough to condense moisture from the basement air. But it’s on the buried side of foundation where the wall is much warmer than the outdoor air. This is what doesn’t add up.
Rule Out Plumbing Leaks
Since the water is one spot only and condensation here is unlikely, I would look for water leakage. I would start by looking for plumbing leaks as they are easier to fix than foundation leaks. Check the bathroom above. Common leaks are the bottom on the toilet tank, the supply line connections, and the toilet flange/wax ring. Plumbing leaks do not always appear directly below the source of the leak as the water can horizontally along a pipe or wood member before appearing below. It’s unlikely to be condensation from your well water supply pipe – but that’s a common problem in warm, humid weather.
If you don’t see anything obvious, you could drain the toilet next time you leave the house, dry the basement floor with a heat gun or hair dryer, and see if the area is wet next time you visit. Adding red dye to water in the toilet tank is another way to determine if it is ending up on your basement wall.
Check For Foundation Leaks
If you can rule out plumbing leaks, that would suggest a foundation leak – most likely near the bottom of the wall. Since it is mid-winter, it is not likely to be a high water table (springtime problem), but rain or snowmelt from above could be running down the foundation wall and finding a way in. If water is pooling against the foundation wall, exerting hydrostatic pressure, it will find a way in unless your foundation is built like a boat.
You’ll have to cut away some materials, dry the area, and watch closely for where the wetness first appears. Pay special attention to where the water is entering the basement. Why the water is showing up mainly on the room side of the vapor barrier, remains a mystery. My guess is that the drywall is wicking the water upward. At a minimum, the bottom plate of the wall should also be wet, moldy, or otherwise degraded. You can check with a moisture meter if nothing is visible.
You did mention that the downspouts go underground. That would be the first thing to check as there is often blockage or broken pipes/loose fittings underground in these systems. If there is a downspout on the side of the house with the leak, temporarily disconnect it and redirect it on the surface to see if that stops the leak. For more immediate results flood the gutter and downspout with a hose to see if the system backs up and water appears in the basement.
Sometimes the solution to these problems is as simple as redirecting a downspout or adding a few splash blocks to redirect surface runoff. Other times, it requires more costly improvements to site drainage and foundation drainage .
If the gutters and downspouts are not at fault, on a warm day, you can run a hose outside the foundation wall for 15 to 30 minutes, or longer as needed, near the problem area. Wait and see if water appears inside at the bottom of the wall.
If none of these investigations are productive, you may have to remove additional finish materials in the leakage area to get a better look. If water is entering at the bottom of the wall, and you cannot solve the problem without excavating on the exterior, you may want to consider adding a sump pump in that corner of the basement.
If you do hire a basement leakage company to diagnose and fix the problem, make sure they guarantee that the leak will be fixed.
Sometimes these problems can be devilishly difficult to figure out. A few years ago, I poured red dyed water down a vent pipe on the roof in the middle of the winter to locate a leak in the kitchen one story down that no plumber could figure out. Turns out a nail had been driven through the vent pipe. Moisture from the plumbing vent was condensing on the cold outdoor section of the vent pipe, dripping down, leaking out the nail hole, and dripping from the kitchen soffit and cabinet 10 feet down and several feet over. Other times, I have cured basement leakage problems by redirecting a drain pipe or adding a splash block.
Our sister site Inspectapedia has an excellent section on basement leakage causes and cures.
— Steve Bliss, Editor, BuildingAdvisor.com
Thanks for all the info. (The red dye thing is genius–I’ll have to remember that one.) We had a basement leak company come and check things out and it seems like the most likely suspect is a blocked gutter and drainpipe. The house is up in the mountains, so lots of snow and ice. We have installed heat tape that looked like it was working, but one part in the gutter itself seems to be broken, so it was pretty iced up.
There was no way to see it without climbing up there on a ladder, but I should have thought about checking that out sooner. We’re fixing that problem and hopefully that helps. There wasn’t much moisture behind the wall, so I think we caught it in time.
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