There are usually two of them at the bottom of the window sash (frame) and they are weep hole covers. There is a top-hinged flap recessed in the slot that only opens outward. The flap is designed to open to allow any water that might get into the voids in the window sash to drain out onto the sill, which is sloped away from the window.

    Gravity keeps the flap closed until the pressure of any water accumulation behind it pushes it outward. Here is one below, held open by a small screwdriver.

    The flap eliminates air infiltration through the frame, keeps insects out, and ensures that debris does not accumulate in the drain slot and clog it. If the flap is missing, as in the photo below, it should be replaced. The red arrow points to the hole when a pin for the missing flap fits into the cover piece. The cover can be pried out with a small blade or screwdriver, and a new one snapped in place fairly easily.

    Here’s a photo of a window weep hole after a heavy, driving rain blew water through the screen and against the window. You can see the trail of water draining down the wall below it from the weep hole.

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  To learn more about doors and windows, see these other blog posts:

• What causes sweating (condensation) on the inside of windows in the winter? 

• Is every exterior door of a house required to have a landing outside? 

• Why does condensation form on the outside of some windows and not others in the morning? 

• Why is the garage door track a white tube? 

• What is the raised metal plate on the floor under the garage door?

• Why do I have to hold down the button to close the garage door? 

• How can I tell if a window or glass door is safety glass? 

What are the code requirements for safety tempered glass for doors?• 

• Should a front door swing in or out? 

• Why is pressure washing double pane windows an expensive mistake? 

• How many exit doors are required for a house?

• Why is a double cylinder deadbolt lock on an exterior door a safety hazard?

• How can I check my garage door to make sure it is safe?  

• What is an egress window?

• Does a home inspector test all the windows and doors in a home? 

• How difficult is it to change a window to french doors or a sliding glass door?

• How do you determine if a door is left-handed or right-handed?

• Why are window security bars dangerous? 

• What are the common problems you find inspecting windows?

• What is causing a foggy haze on my windows? 

• What do those numbers on the manufacturer's stickers in new windows mean?

• What does a home inspector check on an electric garage door? 

• What is the tempered label on glass at windows and sliding glass doors called?

• Do I need to have two exterior exit doors in my house? 

• When is safety glass required for windows at stairs and stair landings?

   Visit our DOORS AND WINDOWS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.