Mold/ wet basement window sill

20 Replies


we fixed the basement window sill a year ago, it was ruined by water leaking from outside as we thought.   I had handyman work on the slab to raise it. The basement window is on the north and irs quite damp outside in the corner there.

Today I saw black mold on that nice window sill that has not been painted yet. I had a contractor to look at it today and he told me to rip it off and to insert some plastic to prevent it from getting wet. 

I do not want to redo the window sill for hundreds of times.  I would appreciate all your thoughts and guesses. And the best way to fix it once and for all,thanks

You will need to figure out where the water is coming from and divert the water.  

Is the window underground with a window well?

Do you have a picture of the outside, be helpful to diagnose the problem. I get called out on water intrusion issues all the time when the crews have exhausted their options. We typically start with a garden hose and use the process of elimnination until we discover the real cause/source. Better to fix the outside then to keep replacing wet windowsills. Trading wood for plastic wont stop the intrusion.

1 the slope out outside might no be enough
2 it is a single glass window with a storm glass outside. Most likely there is too much cold is coming through window and the moisture is from condensation

I would replace the window with a vinyl jamb, make the window a little smaller height wise so it would be raised at least 1" above where it starts right now, do aluminum capping around it a silicone the hell out of it outside

@Larisa Van Valkenburg sorry about the delayed response. 

Could be condensation, but seems awfully wet for condensation.

If I was trying to solve this, I would take a fan set it on the inside dry it real well. Then i would take a hose and run water on the outside, see if it pools up right under the window or if it runs away. If it pools up you need to get the water diverted. I don't know how thick that sloped concrete is, and if water is seeping in under the concrete and in through the window. The only way to tell for sure is to test it. 

We have had to solve a lot of similar water intrusion issues, and many times they are not the first few most logical sources. 

Couple other options

1. if you don't need the window, close it with a cement block

2. You could do a four inch solid cement block and a smaller window

3. Replace the current window with  a glass block window that gets mortared in sealing out water intrusion

But I suspect if you probably divert water from the outside it will solve the problem.

Thank you Dell for your suggestions, I will check it with the water hose, but I can tell you that its coming from the outside, just under the window frame but not sure. I will check everything, I will run the dehumidifier.

The window is very important to me as I am adding the fourth bedroom, so I cannot just close the window.

Thanks every one, I will keep you posted!

I do not know what the codes are in your area, but in Alberta for a bedroom window you need an egress window, the one in the picture is too small for a bedroom to be a fire escape anyway: so new well, cutting concrete, installing new window anyway


when you say "black mold" be careful. it's undoubtedly mold that is black but hopefully it's not caustic "black mold" per se. Besides the other good suggestions you received I would get a professional moisture meter (not a cheap 2/4 prong surface meter) to determine moisture levels throughout the house. if the water damage is just localized you probably don't have a bad situation

MOST excess water problems start higher,,,is this a valley in the roof directly above this area?

AND does the water run away at a fast clip after it gets off the concrete slope?  Is foundation sealed to the concrete apron?

North sides of houses are typically wetter than any other side.  Might start with over size eave and downspouts first and then maybe a french drain/sump pump arrangements (if needed),,,hopefully not.  Natural drainage is best.

IF your making a basement bedroom it really really need the egress window.

IF your walls higher up are moldy start there.  Cant tell what I am looking at with the tear out pics,,,can you take one a bit farther off.???  Proper vapor barrier for your area?

@Larisa Van Valkenburg  

If you are doing your testing with a hose, I would also get of the roof spray water on the roof,  and see if it's coming down behind the gutter, or if the down spout is clogged causing it to overflow and dumping water in the corner, and then not having a place to drain to properly.

In the early years we did many multi thousand dollar "fixes by the pros" that didn't work, that we fixed with proper testing and a bit of proper draining.

Key is to create a path on the outside to get water to drain away instead of soaking into the ground by the window. Water will always take the path of least resistance and flow to the lowest point. 

Hi, first of all there are no gutters on the northern side,we are planning on getting them in near future though. And yes, water just sits in the corner, there is no proper drainage. I am going to make one.

Thanks Steve for telling me about a moisture meter, I have never heard about it. 

This window is double pane and I think I do not need an egress window as the exit door from the basement is two feet away from the bedroom.

Thanks everyone, I am learning tons of information!!!

You currently have an office or a nonconforming bedroom.  Check your codes for the window requirements for a bedroom. 

This window does not meet the requirements for my area.  You need an egress with direct exterior access. You need a window that has a net of 5.0 sq ft of open area to crawl out of.  This window must be located no higher that 44" above the floor.  The width must be 20" net.  This will force you to have a window well and ladder.  This must be 9 sq ft in area and 36" wide as a minimum. This is per IBC 2012 part 1029.  I don't have the IRC 2015 (residential) which is what you will have to follow.  I believe this is the same requirements for both codes.   

For around a $1000 you can have a code compliant bedroom.  Don't forget to get your building permit for the window.

you have moss growing outside your window.. it is wet out there... you are on the right track to 

install gutters and build slope on ground to get water away from your foundation... solve the water issue outside and this should help you inside... and do not drywall the sill again... use tile, plastic, stone....

@Jim Adrian Hi, I have recently purchased a property with basement and windows are about the same size here. These rooms were counted as bedroom on MLS and county record. I plan to flip this property without replacing these window. Will I have any problem. These are grand fathered bedroom for me. any ideas?

Originally posted by @Rao V. :

@Jim Adrian Hi, I have recently purchased a property with basement and windows are about the same size here. These rooms were counted as bedroom on MLS and county record. I plan to flip this property without replacing these window. Will I have any problem. These are grand fathered bedroom for me. any ideas?

I dont think so because you are renovating the house. There is a threshold set by the bldg codes and local bldg dept. A quick call to the bldg dept will confirm this. I am assuming you will need permits for new work and you are doing more that paint and carpet. It can be listed as a non-conforming bedroom. People will use it as a bedroom but it wont meet the legal requirements for one. 

@Larisa Van Valkenburg I would replace the sill with vinyl like some others have said. From the look of that corner, I would say it is draining toward that corner. first thing I would do is grind that stump out of there. Add some dirt, worst case put some drain tile in sending the pooling water away from that corner.

good luck

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