| Local Building Code |
The legally adopted code depends on the city, state, province, or country. A model code is not automatically the enforceable code. |
- Confirm the adopted residential or building code edition.
- Check local amendments, historic-district rules, and permit requirements.
- Determine whether the project is a replacement, alteration, or change affecting structural openings.
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Obtain written requirements from the local building department before selecting window sizes, glazing types, or installation methods. |
International Code Council model-code framework; local authority having jurisdiction controls enforcement. |
| Thermal Performance |
Lower U-factor means better resistance to heat flow. U-factor is normally reported in Btu/h·ft²·°F; lower values indicate better insulation. |
- Compare the complete window unit, not only the center-of-glass value.
- Review frame, sash, spacer, and glazing effects.
- Use the climate zone and the locally adopted energy code as the minimum reference.
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Choose a unit whose certified whole-product U-factor meets or exceeds the applicable energy-code requirement, while avoiding unnecessary over-specification for the climate. |
International Energy Conservation Code performance tables; National Fenestration Rating Council certification practice. |
| Solar Heat Gain |
Lower SHGC reduces unwanted solar heat gain; higher SHGC can provide useful passive solar heat in heating-dominated locations. |
- Evaluate orientation: south- and west-facing windows often receive stronger solar exposure.
- Consider shading, overhangs, blinds, and cooling loads.
- Check both code limits and energy-program criteria applicable to the project.
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Use climate-appropriate SHGC rather than selecting the lowest possible value for every elevation. |
Energy-code fenestration provisions and certified window energy ratings. |
| Air Leakage |
Air leakage is reported in cubic feet per minute per square foot of window area at a specified pressure. Lower certified leakage generally improves comfort and energy performance. |
- Review the tested air-leakage value on the product label or certificate.
- Inspect the rough opening, perimeter seal, and operable hardware.
- Do not assume a high-performing window will compensate for a poorly sealed opening.
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Specify a certified product with low air leakage and require continuous perimeter air sealing during installation. |
NFRC product-rating procedures and applicable fenestration performance standards. |
| Emergency Escape and Rescue |
For many sleeping-room locations under the International Residential Code, the emergency escape and rescue opening requires at least 20 inches clear width, 24 inches clear height, 5.7 square feet net clear opening, and a maximum sill height of 44 inches above the floor. The minimum area is commonly 5.0 square feet at grade-floor openings. |
- Measure the actual net clear opening, not the nominal window size.
- Confirm whether the room is a sleeping room and whether the opening is at grade level.
- Check window wells, ladders, steps, and obstructions where applicable.
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Choose a window configuration that meets the required clear-opening dimensions after installation and interior trim are complete. |
International Residential Code, Section R310; local amendments may differ. |
| Safety Glazing |
Safety glazing is generally required in hazardous locations, including glazing near doors, in doors, and in specified areas close to floors, walking surfaces, tubs, showers, and other impact-prone locations. |
- Map all glazing locations against the locally adopted safety-glazing rules.
- Look for permanent safety-glazing identification where required.
- Consider laminated glazing where fall-through resistance, sound control, or post-breakage retention is important.
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Use safety glazing where required by code and document the glass type on the order and installation records. |
International Residential Code, Section R308; local code provisions control. |
| Water Management |
Replacement windows must be integrated with the wall drainage plane so water is directed to the exterior rather than into the wall assembly. |
- Inspect sill conditions, flashing, end dams, head flashing, and side integration.
- Check whether the existing water-resistive barrier is damaged or discontinuous.
- Use installation details appropriate for the wall type and exposure.
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Require a written flashing and sealing sequence, compatible materials, sloped sill drainage, and an exterior sealant joint that is not used as the only line of defense. |
Building-code water-resistive-barrier provisions and recognized window-installation standards. |
| Condensation Resistance |
A higher condensation-resistance rating indicates better resistance to interior-surface condensation under the rating method used. |
- Consider indoor humidity, winter temperatures, frame material, edge spacer, and interior air circulation.
- Pay special attention to bathrooms, kitchens, bedrooms, and cold-climate installations.
- Check for thermal bridges around the rough opening.
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Prioritize a strong condensation-resistance result in cold or humid conditions and maintain reasonable indoor humidity with adequate ventilation. |
NFRC condensation-resistance rating methodology; actual site conditions may differ from laboratory ratings. |
| Sustainability and Durability |
A sustainable window decision includes operational energy use, service life, repairability, material impacts, moisture resistance, and disposal—not only recycled content. |
- Request environmental product information where available, such as an environmental product declaration.
- Check expected service life, replaceable hardware, warranty terms, and maintenance requirements.
- Evaluate frame material, coatings, sealants, and the possibility of future glass or hardware replacement.
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Select a durable, repairable product with verified performance documentation and avoid replacement solely on appearance if the existing window can be effectively restored. |
Life-cycle assessment principles and green-building project requirements; specific documentation depends on the chosen rating system. |
| Installation Tolerances |
The rough opening must provide adequate clearance, a level sill, plumb jambs, a square frame, and secure fastening without distorting the window. |
- Measure width and height at multiple points.
- Check diagonals, sill slope, jamb condition, and hidden water damage.
- Allow for shims, insulation, movement, and manufacturer-specified fastener locations.
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Measure each opening individually; do not order all windows from one nominal dimension unless the openings have been verified to be uniform. |
Manufacturer installation instructions, applicable fenestration installation standards, and local code requirements. |
| Ventilation and Operation |
Operable windows can support natural ventilation, but ventilation must not compromise fall protection, insect control, weather resistance, or emergency egress. |
- Confirm opening direction, hardware reach, screens, restrictors, and cleaning access.
- Check whether restrictors could prevent required emergency escape.
- Coordinate window operation with furniture, cabinetry, and exterior landscaping.
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Choose operation types that match room use, cleaning needs, ventilation strategy, and required clear-opening dimensions. |
Local building and safety provisions; project-specific ventilation design requirements. |
| Documentation Before Purchase |
A complete specification should identify dimensions, operation, glazing, U-factor, SHGC, air leakage, safety glazing, color, flashing method, and installation responsibility. |
- Obtain a product performance certificate or permanent rating label.
- Confirm the certificate applies to the exact size and configuration ordered.
- Keep permits, inspection records, photographs, and installation instructions.
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Use a written window schedule and require approval of substitutions before delivery or installation. |
Fenestration rating documentation, building-permit records, and project quality-control practice. |
