Author Brian Tenace
Welcome back to my multi-part series about water resistance in windows and doors. Last time we discussed weatherstripping. Today, we move on to a product common to sliding doors and coastal areas – sill risers.
Sill risers offer a brute force way to reduce water infiltration when a LOT of water is expected to hit a fenestration product. Unlike weathersealing, buried drainage, or weep systems, sill risers block water by providing a dam. Coastal homes with wind driven rain frequently have sill risers. They are practical and require less maintenance than weep holes or buried drainage systems, plus manufacturers can customize riser heights for more or less severe water pressures.
A PVC Sliding Glass Door. The inner wall of the frame provides a ledge to prevent water ingress. For a higher water infiltration resistance, the easiest solution is to make the innermost wall taller by using a sill riser.
A sill riser functions as an add-on to the sill (bottom of a window or sliding door) that rises above the bottom plane. The figure below shows a sill riser on a sliding door. Normally it is added by the window/door manufacturer as an integral part of the product based on building code water resistance requirements. Some sliding door manufacturers use modular snap-on sill risers that can be added or replaced.
When I lived in Miami in the early 2000’s, I observed water bubbling under sliding doors on numerous occasions during major rain events. The sill risers on doors allowed that water to rise 1-2 inches above the sill track without entering the building interior. Although alarming, a functioning sill riser lets the water level rise until the rain (or even minor flooding!) event subsides. After the exterior pressure relents, the captured water drains back outside along its typical path.
A sketch of a generic sliding door. The sill riser (blue) acts as a brute force method for increasing water infiltration resistance when high water pressure or large watershed areas otherwise overwhelm openings. These conditions are typical for oceanfront homes in coastal regions such as Florida, South Carolina, and Texas.
Benefits
Sill risers offers the following benefits:
- Great for flood-prone areas and high pressure (wind driven) rain events, or windows/doors with big tributary areas (such as tall oceanfront sliding doors).
- Sill risers are self-contained and often retrofit-ready. Many PVC window and sliding door manufacturer profiles have grooves on the inside faces that accept sill risers. Even a galvanized plate can act as a sill riser if properly attached.
Drawbacks
Sill risers present unique challenges:
- Improperly installed risers present major leakage concerns at corners.
- ADA compliance is usually impossible. The sill riser is essentially a step. Depending on the installation, that step can become a tripping hazard, too!
- Sill risers only work on outswing or sliding products.
- Unsightly cracks can develop near sill risers. Tall risers can bend due to lack of support. Bent outward, a sill riser can impede the operation of sliding components.
Possible Damages/Issues
Bent or poorly installed sill risers can leak. Inattentive installers may not take into account the height of a riser, producing tripping hazards.
Sill riser failures can manifest similarly to weep holes, although generally they do not involve glazing failure (fogging) of insulated glass. Water overwhelms sill risers and spills over the edge to the inside, where it frequently runs along and/or down the door frame. Much as with weep hole failure, 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.
Unlike weep hole failures, however, improperly installed sill risers can allow water around the perimeter of the sill riser. This results in more insidious damage. Water infiltrates below flooring. In slab homes, the water can become trapped between finished flooring and concrete. Wood substrates can allow water to enter the crawlspace or run along floor joists. Depending on the frequency and quantity of leakage, improperly installed or damaged sill riser joints can go undetected until they’ve caused damage to a huge area.
Effective sill risers offer a “brute force” dam to keep water out of an interior space. Clean installations block water from heavy driven rains and even minor flooding. Skilled forensic engineers with fenestration certification from FGIA are ideally suited for identifying whether sill riser 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.
