Tom Shafer

What are the small square holes in window frames?

June 09, 2011

Whatever are those small square holes doing on the exterior frame of your new vinyl replacement windows? Won't the little holes let cold air in, just when you thought replacing your wood or aluminum windows would get rid of drafts? Don't cry. These are your window's weep holes, and they are strategically placed to drain water out of your window while preventing airflow into your home.

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Weep holes: a critical window design feature

Water flows with gravity, downhill, which is the principle used to drain water away from a wood or aluminum window instead of into your home. That is why most wood windows have a sill that slopes away from the window. During a rain storm water hits the outside of the glass, dropping to the sill and draining away from the window.

Many vinyl replacement windows, however, are made on all four sides from the same extrusion, the technical name for the lineal vinyl piece that is cut into sections and welded together to form the frame. The reason you need weep holes is because the sill is the exact same-shaped extrusion as the jambs, which means that the window tracks that hold the sash when in the vertical position of the frame will collect and hold water when functioning as the sill in the bottom horizontal position of the frame. Weep holes allow this water to drain.

Cross-section showing how weep holes work

Diagram of how weep holes work - credit Milgard

No wind in the weep holes

So, if there are holes to drain the water out, won't they also allow wind to come in?

Vinyl window manufacturers have anticipated your concerns and have solved that problem in a variety of ways:

  1. Little doors or flaps are inserted to cover the weep holes. They open outward when water is exiting the window and close to prevent wind pushing against them to get into the window.
  2. The extrusions are filled with a network of compartments designed primarily to give added strength to the frame, but these chambers also act as baffles against the incoming air, preventing it from entering the house.
  3. The exterior weep holes that drain the water out of the window are not aligned with the interior weep holes; thus, they block direct air flow into the window.

Window maintenance and debris-free weep holes

Most sliders have weep holes, as do most double hung replacement windows. Weep holes on sliders can be seen in the sill track. They are under both the sliding and operating sash, as well as the screen. Vinyl patio doors may have weep holes also; some are on both the top and bottom, but this is only so the door can be rotated during installation to reverse its operation.

Care is necessary to assure access to weep holes is kept clear. No caulking or exterior sidings should be allowed to cover the holes. The opening should always be kept clean.

Do not let dirt block the weep holes

Do not let weep holes get clogged like this - credit http://www.carolinaecosmart.com/

Check regularly for dirt, dead bugs, leaves and pine needles that can block drainage. Remove debris promptly to prevent water from backing up into your home and causing damage.

Keep your weep holes happy and you will never need to shed a tear about water (or wind) breaching your vinyl windows.

About the Author

Tom Shafer has decades of experience in window sales, marketing and product development. He's worked closely with window design engineers in testing, design, and building code interpretation. Past employers include United Windows and Doors and Norandex, MI Windows. He currently works at a home improvement retailer.

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