| Casement | Side-hinged sash that opens outward | Can close firmly against weather seals; opens widely for ventilation | Check exterior clearance, hardware quality, and resistance to wind-driven rain | Whole-window U-factor, air leakage, water resistance, operating hardware |
| Tilt-and-turn | Typically tilts inward for ventilation or swings inward for access | Offers multiple opening modes and can provide a tight closed seal when properly made and installed | Confirm hardware load capacity, opening clearance, and availability of replacement parts | Tested air and water performance, hardware cycle rating, glazing options |
| Sliding | One or more sashes move horizontally along tracks | Requires no outward or inward swing space; convenient for wide openings | Track drainage, cleaning access, rollers, and sash-lock engagement affect long-term use | Air leakage, drainage design, track materials, operable-sash dimensions |
| Fixed / picture | Non-opening glazed unit | No operable sash; often a suitable option where ventilation is not needed | Plan ventilation elsewhere and ensure the glass can be cleaned safely | Whole-window thermal rating, glass safety requirements, frame-to-wall detailing |
| Awning | Top-hinged sash opens outward | Can allow ventilation during light rain, depending on design and weather exposure | Check projection clearance, wind limits, and hardware durability | Water-resistance test results, air leakage, hinge and operator specifications |
| Bay / bow | Multiple window units project outward at an angle | Adds interior space and can increase daylight and outward views | Requires careful structural support, weatherproofing, and installation planning | Structural details, roof and sill flashing, unit ratings, installation requirements |
| Energy-bill context | The U.S. Department of Energy estimates that replacing single-pane windows with ENERGY STAR certified windows can save 7–15% on annual household energy bills. Actual savings vary with climate, energy prices, window area, existing conditions, and installation; this is an estimate, not a guaranteed result. |