Author Brian Tenace
Welcome back to my multi-part series about water resistance in windows and doors. Last time we discussed weep holes. Today, I’d like to talk about weatherstripping (also known as weathersealing).
During the life of typical exterior fenestration products, every driven rain is a test of the product’s water weathersealing system. Most windows and doors handle water without much homeowner input, but racked or misaligned windows, poor weatherstripping corner joints, and torn piles all contribute to reduced water infiltration resistance. They can allow moisture into the structure, where damage to flooring, walls, and molding may occur.
Weatherstripping and sealing acts to center sliding sashes and sliding doors. It often involves soft polypropylene felt or even EPDM with myriad variations in pile (felt) height, impermeable plastic flaps and integral low-hardness PVC’s. But the main use of weatherstripping is water and air infiltration resistance.
Single hung window, viewed from inside showing weatherstripping on the sill and on the sliding panel’s side rail. Note how the sill channel extends beyond the jamb, creating an overcompressed section of weatherstripping. Manufacturer issues such as this can cause water leakage by creating gaps in frame components. Gasket seals are common for swing doors, while loose “pile” felt weatherseals such as those shown above are more common for sliding products. Note how the weatherseals allow for continuous contact of the sliding sash with the frame, reducing the amount of air infiltration and positioning the sash in the frame.
Weatherstripping is the primary line of defense against water at window joints. Plastic, EPDM and co-extruded PVC seals offer good blocking for heads and sills on horizontal sliding products. Even soft felt reduces water if properly compressed. Weatherstripping allows manufacturers to place gaps between their hard sliding and fixed components to ensure smoother operation.
Benefits
Weatherstripping offers the following benefits:
- PVC and Aluminum profile grooves can accept a huge range of profiles from hard to soft, short to tall.
- Weatherstripping can be retrofitted and replaced in most existing windows. Relatively inexpensive adhesive offerings for around $1/ft. are readily available in hardware stores.
Drawbacks
Weatherstripping does not drain water, however. Some drawbacks include the following:
- Tight tolerances can tear or reduce efficacy of weatherstripping seals.
- Poor installation by manufacturers or installers eliminates any benefit weatherstripping provides. I’ve seen countless instances where manufacturers welded PVC sashes with weatherstripping in place, creating voids at corners. Other times, a slide-in piece has snagged and fallen partway out during assembly, leaving a gap in the seal.
- As the old window adage goes: a window is only as good as its installation. Ideal weatherstripping compression ranges from 15-50% depending on the design. Racked or misaligned window installations overcompress (or undercompress) seals. Weathersealing does a good job of masking imperfections, but this can worsen the potential for leakage!
Possible Damages
Missing, damaged or compromised weatherstripping allows water and air to infiltrate the window or door.
Water from weatherstripping failure can enter glazing cavities on virtually any corner of a window. Poor gaskets around glass may result in glass fogging, which reduces insulated glass energy efficiency and visible transmittance. In a similar fashion to weep hole failures, water can overwhelm weatherstripping and spill over the edge of the inside, where it frequently runs along and/or down the window frame. Damage typically 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 all the way to the floor, where localized delamination of flooring and even substrate damage along the wall/floor interface will occur.
Water damage from failed weatherstripping normally manifests with insect problems and a “halo” effect of discoloration or fungal growth around the sill of a window, but unlike weep hole issues alone, weatherstripping failures are more likely to lead to damage around jambs.
Effective weatherstripping reduces air infiltration and improves water infiltration resistance of fenestration products. Clean installation with plumb, level and unracked sashes allows properly manufactured weatherstripping to block most water from entering a window’s weep system. 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.
