Reuben's Home Inspection Blog


Window Stains: When To Be Concerned

Water stains on window sills is often a source of anxiety for home buyers, and it's the home inspector's job to help determine if the stains are the sign of a major problem or not. There are three common causes of water stains on windows:

  • Leaving the windows open.  The windows get left open, and water pours in through the window during a rain storm.  This type of staining will often leave fairly uniform water staining across the window sill.
  • Condensation Staining at windowCondensation.  If it's a wood window, you'll see stains at the corners of the window sashes and the window sills if the stains are caused by condensation.  You'll also find the worst stains on the windows that are most likely to be damp, such as in bathrooms or bedrooms just outside the bathrooms.  The windows at the north side of the house will be worse than windows on the south side.
  • Leaking windows. If water is actually leaking in to the house around the opening for the window at the siding, this will typically show up as staining at the corners of the window sills.  The photo below left shows what a window sill may look like with minor water leakage in to the wall; the photo below right shows a window sill with major damage from water leakage.  A home inspector could use a moisture meter to help determine if the stains are currently damp.  These are the stains to be concerned about.

Water staining at window sill from minor leakage Water staining at window sill from major water leakage

The first two causes of stains are fairly straightforward and easy to prevent; remember to close the windows before it rains, and lower the humidity in your home.  Here are a few tips to lower the humidity in your home:

  • Turn off your whole house humidifier (duh)
  • If you have one, use your kitchen exhaust fan when you're cooking.  Gas ovens add a considerable amount of moisture to the air.
  • Turn on your bathroom exhaust fan during showers and leave them on for a half hour after every shower.  If you don't have a bathroom exhaust fan, get one.  While the building code allows an openable window as a substitute for a fan, I don't ;-)
  • If you have a crawl space, make sure that a proper vapor barrier is installed on the crawl space floor.
  • Install an HRV or a continuous exhaust fan.  Either one of these will dramatically lower humidity levels in a home.

The third cause of staining at windows, leaking water from the exterior, is the one that home buyers should be concerned about.  A window can leak from just the slightest defect in flashing at the top, and unfortunately, it's not easy for home inspectors to know if a window is going to leak just by looking at the siding.

View of window from outsideIf the flashing above a window is installed properly, all of the water coming down the siding will be diverted around the sides of the window.  The windows that will be exposed to the most water are the windows that aren't protected from rainwater by soffits and gutters - such as the window shown at left.

The photo below shows the proper path for the water to take; I know this is kind of a 'no-duh' issue, but actually thinking through this stuff helps me to know which windows I really need to pay particular attention to during home inspections.


Proper Water Path

Here's a close-up view of the window flashing, showing the path that water is supposed to take... but this window has a nasty detail in the flashing that will be prone to leakage.  Do you see it?

Proper Water Path closeup

Here's another close-up view, pointing out the exact issue with the flashing.

Proper Water Path closeup 2

As you can see in the photo above, if the caulking at the J-molding around the window fails, the window is going to leak.  Big time.  As a matter of fact, it has failed at this particular window, and that's what is causing the major water staining at the bottom of the sill, which is what was shown above.   Could you tell just by looking at the exterior of the window?  I couldn't.

The repair for this condition is to have the flashing redone, so the window isn't relying on the caulking to keep water out.  This project will probably only take about an hour or two to complete, but it would have taken the original installer an extra two minutes to get it right.  My first thought was that the installer was either lazy or a bonehead, but at the time this window was installed, which was about twelve years ago, this was just the way it was done.

If I saw an installation like this on a relatively new home, I'd call it a boneheaded installation.


Reuben Saltzman, Structure Tech Home Inspections


Comment balloon 29 commentsReuben Saltzman • August 13 2011 06:30AM


Reuben: Great post. Now I know what those ugly things around my windows are doing. And no leaks - so I guess they aren't so ugly after all! I like to reblog universal content and will stop back later to do so. Thanks for a very informative post!

Posted by Anne M. Costello (Weidel Realtors) almost 8 years ago

It's probably due to boneheaded caulking!  Good explanation Reubs.  How often do we see this, particularly on a southern or western face?

And I like Jay molding...

So, what did you see in the stain on that wood trim?  Lips?  Porcupine?  Hedgehog?  Basement water beetle?

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

Great post !  This is something not seen oncommonly in lots of areas....and now more wisdom on the subject !

Posted by Sally K. & David L. Hanson, WI Realtors - Luxury - Divorce (EXP Realty 414-525-0563) almost 8 years ago

Anne - yeah, those ugly things around your windows are only there to help :)

J-Molding - I suppose that could have been boneheaded caulking, but what's boneheaded to me is the fact that someone relied on caulk to keep the window from leaking.  

What I didn't happen to mention is that this is my house.  I fixed it by taking the upper course of siding off and applying a little flashing tape underneath everything.  Problem solved.  

Funny, that does look like a rorschach test!  All I saw was more work for myself.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 8 years ago

Sally & David - thanks for reading!

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 8 years ago

You are right about relying on caulking.  People think it's permanent.  And the siding guys, or builders, seem to favor that $.89/tube butyl stuff...

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

Hi Reuben: Thank you for the nice informational post..  Best, G

Posted by Gay E. Rosen, As Real as Real Estate Gets! (Julia B. Fee Sotheby's International Realty) almost 8 years ago
That is interesting. The photos help understand the point much better.
Posted by Cheryl Ritchie, Southern Maryland 301-980-7566 (RE/MAX Leading Edge almost 8 years ago

Extremely useful information. Appreciate the information.

Posted by Peggy Duffy (The Bailey Team Real Estate) almost 8 years ago

Reuben - Your idea of getting a bathroom exhaust fan installed in a bathroom with a window is a good one.  Many people never open their bathroom windows.

Posted by FN LN almost 8 years ago

I remember an inspection I did during a thunderstorm. Water poured in the bay window in the kitchen. I was told it was "fixed" by recaulking the window, Doh!

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) almost 8 years ago

Thanks for the heads up, Reuben.  We just installed a fan in house that Community Housing Partners over insulated.  The house was so tight, we had to put a fan in that runs all the time (their idea, not mine).  Moisture build up was causing more issues than the formerly leaky house. 

Posted by Mike Cooper, GRI, Your Neighborhood Real Estate Sales Pro (Cornerstone Business Group Inc) almost 8 years ago

Reuben, just did a lease where a couple of the windows were leaking and caused a mold problem beneath the wall paper. The inspector (Jay Markanich) found the source and the owners remedied the problem.

Posted by Michael Setunsky, Your Commercial Real Estate Link to Northern VA almost 8 years ago

A house is like a car where everything has to work together for a purpose. I love talking with the the different tradesmen because they know how to apply their trade correctly to become part of the whole. Good learning post

Posted by Richie Alan Naggar, agent & author (people first...then business Ran Right Realty ) almost 8 years ago

Thanks for the tips.  But what is and what does a continuous exhaust fan look like?


Posted by Morris Massre, Real Estate Instructor Broward County Florida almost 8 years ago

Jay - you get what they pay for.

Gay - thanks.

Cheryl - thanks, this stuff is nearly impossible to explain without photos.

Peggy - thanks for reading.

Marc - especially not in the middle of winter, when it's most needed. 

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 8 years ago

This is always a second rate installation detail for me, and I don't care how many people try to tell me it's standard, it's not. 

For this reason I hate to see J-mouldings used as header flashings and any caulking reliant detail is a red flag for me.

Good issue to profile in your blog Reuben. Thanks.

Posted by Robert Butler, Montreal Home Inspector | Aspect Inspection (Aspect Inspection) almost 8 years ago

James - it would have sounded a lot better if they had just said "they fixed it."

Mike - you can't overinsulate a house ;).  Putting the continuous fan in was probably a good fix in this situation.

Michael - good for Jay!  I hope the owners fixed it properly.

Richie - absolutely.  Everything works together.

Morris - a continuous exhast fan is basically a bathroom exhaust fan with a motor that's rated for continuous operation.  Some of these models will run constantly at a low speed, and will kick in to high speed when a button is pushed or a switch is flipped.  Here's an example of one -

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 8 years ago

Hello Reuben!  Great Post!!  Thanks for the detail photos!  Aren't wood windows supposed to be stained?!!

Posted by Rob Smith (Rob Smith Property Investigations) almost 8 years ago

Thanks for the added 'duh' comment for all the DIYers. LOL. Great pictures.....see you Monday!

Posted by Shar Sitter, Home Staging and Redesign Minneapolis/ St. Paul, M (Rooms With Style) almost 8 years ago

Ah yes Reuben, moisture, the root of all evil. If more people understood this.....

Posted by John M. Scott, Broker / Owner San Francisco Bay Area (BRE # 01442690, Scott Keys Properties) almost 8 years ago

Reuben: Here in southern California, we don't see many homes with vinyl siding (there are a few). With stucco, it is impossible to tell if a window has been improperly flashed by looking at the exterior, so you need to check the interior closely for evidence of water intrusion.

Posted by Steve Stenros, CREIA MCI, ICC, ACI Home Inspector,San Diego (Poway,La Jolla,Del Mar,Mira Mesa,Carlsbad,Escondido,Temecula) almost 8 years ago

Good Morning Reuben, excellent input for home owners.  They need to be educated on cause and effect if they want their home to last.

Posted by Dan Edward Phillips, Realtor and Broker/Owner (Dan Edward Phillips) almost 8 years ago

One thing for sure.  A person cannot buy a home and fail to maintain it. 

They either pay for or do home maintenance from the beginning or pay big time for deferred maintenance when they sell.

Posted by Lenn Harley, Real Estate Broker - Virginia & Maryland (Lenn Harley,, MD & VA Homes and Real Estate) almost 8 years ago

Rob - yes, wood windows are supposed to be stained.  The windows pictured here are vinyl, and that was wood trim inside the house, which was stained.  Oh, wait a minute... I just got it :)

Shar - we're looking forward to it, thanks!  You'll get to see this window in person.

John - that's correct.  It makes up the majority of the problems I find during home inspections. 

Steve - I hear you.  I recommend invasive moisture testing on pretty much every stucco house built since the late eighties.  According to Russell Ray, this type of testing doesn't happen in your area, but it's pretty standard around here -

Dan - thanks!

Lenn - absolutely.  You pay a little today or a lot tomorrow.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 8 years ago

Good information for every homeowner, Reuben, I want to re-blog this for my readers...

Posted by Chris Smith, South Simcoe, Caledon, King, Orangeville Real Esta (Re/Max Chay Realty Inc., Brokerage) almost 8 years ago

Yeah, the termite guys out here are always poking the window sills looking for damaged wood.  You're right, it's a common issue.

Incidentally, I grew up in L.A. San Fernando Valley across the street from a Linda and Terry Saltzman. Her dad was a builder.  Any relationship? 

Posted by Lloyd Binen, Silicon Valley Realtor since 1976; 408-373-4411 (Certified Realty Services) almost 8 years ago

Hey Chris - please do, thanks!

Lloyd - no, I don't know a Linda and Terry Saltzman, but they sound like fine folks ;)

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 8 years ago

Bad Termite los angeles offers full inconvenience of fumigatiohome warranties on their termite control services without the inconvenience of fumigation.

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