01Two key ratings
Windows, glazed doors and skylights are fenestration. Two ratings matter most for energy documentation. U-factor describes how readily heat flows through the whole product; lower values mean less heat flow. Solar Heat Gain Coefficient (SHGC) describes how much solar heat passes through; the preferred value depends on climate zone, orientation and design goals. Ratings typically come from a certified product label or manufacturer data.
02Area and orientation
The total glazed area, and the direction each window faces, influence results. Large glazing areas can make compliance harder, particularly under the prescriptive approach. Performance modeling can sometimes balance extra glazing with better products, shading or other measures. Running a few options before elevations are final is often worth it.
03Keep the schedule and the order aligned
Documentation assumes specific ratings for each window. If the windows actually ordered differ, perhaps because of a supplier change or a value-engineering decision, the documentation may need revision. Inspectors may check labels on installed windows. Keeping the window schedule, the documentation and the purchase order in agreement avoids problems.
04Checklist before ordering
Before placing a window order:
- +Confirm sizes and quantities against the window schedule
- +Confirm U-factor and SHGC against the documentation
- +Ask the supplier for rated product data for the exact configuration
- +Discuss any substitution with the preparer before ordering
- +Leave labels on until after inspection
05Historic and special windows
Projects preserving or replicating historic windows may face constraints. Discuss options early; performance trade-offs may help. Requirements depend on scope and jurisdiction, so confirm with your reviewer.
06Common pitfalls
Frequent issues include substituting a similar-looking product with different ratings, ordering based on center-of-glass values instead of whole-product ratings, overlooking glazed doors and skylights when totaling glazing area, and forgetting that window replacements in an alteration may have their own requirements. Each is easier to avoid than to correct: compare every product against the documentation before ordering, and ask the supplier for the rating that applies to the exact configuration being purchased, including frame material, glass package and any grids or special coatings. Keeping a simple spreadsheet that lists each opening, its documented ratings and the ordered product makes the comparison quick and gives the inspector a clear reference.