Water Removal In Windows and Doors – Part 1: Weep Holes
Leave a CommentIn architecture, the word fenestration is used to encompass the windows and doors in a building. During my twelve-year career as a design engineer in the fenestration industry, water infiltration resistance (I.E., stopping leaks) consumed almost as much time in the test lab as pressure or impact testing. During the life of typical exterior fenestration products, every driven rain is a test of the product’s water evacuation system. Most windows and doors handle water without much homeowner input, but poor, clogged or covered water drainage systems can allow moisture into the structure, where damage to flooring, walls, and molding may occur. Poor water infiltration resistance also increases the humidity in a living space.
PVC Sliding Door w/screen and track weep holes. Note how the weep hole in the lower slot is filled with clay. A weep hole cover should be installed in the slot to prevent more dirt or insects from blocking the slot. Without the slot, the sliding door tracks would collect water and overflow.
There are a handful of ways manufacturers address water infiltration resistance. Ideally, the glazing (adhesive, extrusions or other methods employed to hold glass into a window or door frame) blocks water. Low pressure water and mist intrusion can be mitigated with weatherstripping seals around sashes and doors. But many PVC and aluminum windows manufactured in the last 30-40 years also take advantage of the hollow nature of sills (bottoms of windows/doors) to utilize weep systems.
Today I’d like to discuss the benefits, drawbacks, and failure modes of weep hole systems in fenestration products.
Inswing casement window cross-section showing weep hole. Note how the hollow cavities must create positive drainage pressure on the weep hole to “pull” water out of the shallow passage. Without a weep hole, water would quickly spill into the home.
Benefits
Weep holes offer the following benefits:
- They are relatively unobtrusive. A weep hole size as defined by the International Code Council (ICC), R703.8.6 is a minimum 3/16-inch diameter hole for brick construction. For windows and doors, industry standard weep holes are 3/16-inch X 5/8-inch or larger slots.
- The hollow extrusions used for energy efficient PVC or aluminum frame windows can have weep holes integral to the window product. This makes for easier retrofit where product needs to be replaced. With modern welded PVC frames, weep holes make sense because they allow the manufacturer to use a similar extrusion for the frame sill, header and jambs (thus allowing for full 4 corner welding).
- The height differential of frame holes allows excellent drainage for hollow framed windows. A 2-3 inch rise typical to hollow frames means the positive water pressure can empty out the sill beneath a sash or the ledge where a fixed window sits.
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Weep hole cover. These readily available parts prevent dirt and insects from blocking weep holes.
When used in conjunction with weep hole covers and weather seals, weep holes can provide excellent water infiltration resistance against flooding events. Weep hole covers offer simple mechanical flaps that close under negative pressure, preventing water, bugs or dirt from moving up into the window.
Drawbacks
Unfortunately, weep holes face special challenges:
- They require a hollow beneath the frame. Swinging doors typically have “solid” sills that sit directly on flooring substrate. Casements and awnings sometimes use angled sills.
- Weep holes are easily obstructed by insects or dirt. Particularly in the south, hornets are known to build their nests in uncovered weep hole slots.
- Sometimes, windows are misinstalled or homeowners place exterior substrates on top of weep holes, inadvertently covering up the drainage holes. I have seen and heard of homeowners who seal weep holes with caulk in an attempt to stop water intrusion!
- For doors, weep holes only work when the sill is stepped up from the outside, which is generally not ADA compliant.
- Poor machining of weep holes leads to poor fit of weep hole covers, and installers typically do not inspect weep hole cover fit.
Possible Damages
Wall/Floor damage from overflowing window sill
When weep holes become blocked or inoperable, they can cause water to infiltrate the window or door.
Water damage from weep hole failures usually starts small. Water builds below the sash or glass when there is light precipitation or water is sprayed on a window. It stagnates below the sash or glazed unit with nowhere to go. In fixed units, the life of insulated glass can be decreased substantially by the presence of standing water on sealant. This can cause insulated glass to “fog,” which is considered a failure of insulated glass.
More water defeats the sash or glazed barrier in the window or door. Water then spills over the edge of the inside and runs along and/or down the window frame. This type of damage manifests as fungal growth or soft spots in drywall, followed by separation and expansion of the walls. Long term water infiltration leads to wall damage. Larger flows of water will make their way along the floor, where localized delamination of flooring and even substrate damage along the wall/floor interface will occur.
Water damage from blocked or otherwise non-functioning weep holes normally manifests as a “halo” effect of discoloration or fungal growth around the sill of a window. I have seen similar patterns from amateur installers who install picture windows with weep holes on the tops instead of the bottom, where water has nowhere to go. Overzealous pressure washers are also culprits in weep hole failures when water evacuation rate cannot match the water sprayed on lower DP (design pressure) residential windows typical to non-coastal installations. Water overcomes the drainage capacity of weep holes and bubbles up inside a home or business.
Weep holes provide drainage for fenestration products that take advantage of modern hollow-framed window and door technology. While failure can usually be prevented by routine inspections and cleaning, damage includes wall and floor deterioration, as well as fungal growth. Skilled forensic engineers with fenestration certification from FGIA are ideally suited for identifying whether weep hole failures originated with the manufacturer, installer or somewhere else. Give us a call at The Warren Group if you would like to discuss fenestration-related leakage issues.
Brian Tenace is a Licensed Professional Engineer and holds a FenestrationMaster® Professional Certification. He has over 15 years of manufacturing and machine design experience in production and quality-driven environments. Brian earned a Master of Science in Mechanical Engineering from the University of Florida. Over his engineering career, Brian worked in fenestration design in addition to designing hardware, above/below ground spill containment vessels, extrusions, dies and molds. He conducted root cause analyses for fatigue, weld, and corrosion failures in steel, springs, pressure vents and sheet metals. He developed tests according to standards and custom specifications as needed, along with modifying manufacturing processes. His failure analysis experience includes impact testing, design for ballistic protection, water infiltration resistance and corrosion. Brian has an in-depth knowledge of many standards with emphasis on fenestration standards and impact standards. Brian regularly investigates property damage claims involving machinery and equipment in a variety of environments, as well as personal injury, wrongful death, and product liability claims for both insurance adjusters and attorneys.
