What size egress window do I need for a basement bedroom?

Per IRC R310, grade-floor and below-grade openings need a net clear opening (NCO) of at least 5.0 sq ft (the exception in R310.2.1); upper-floor sleeping rooms need 5.7 sq ft. Minimum net clear height 24", net clear width 20", and maximum sill height 44" above the finished floor. A 32"×60" double-hung typically delivers about 4.8 sq ft of NCO and FAILS — the meeting rail and the fact that only one sash operates cut the available area roughly in half. A casement at the same rough opening usually passes because the entire sash swings out. For basements, the window well also needs to be at least 9 sq ft of horizontal projection at grade with 36" minimum projection and width, and a permanently affixed ladder if depth exceeds 44".

Do I need tempered glass next to my door?

Per IRC R308.4.2, glazing within 24 inches of either side of a door swing must be tempered (or laminated, or wire glass) when the bottom edge of the glass is less than 60 inches above the floor. The rule covers both swinging and sliding doors. A separate rule, R308.4.5 (updated in 2021 IRC), requires safety glazing in walls containing or adjacent to a tub, shower, spa, or pool when the bottom edge is less than 60 inches above the standing surface. R308.4.6 adds a stair / ramp trigger when the bottom edge is less than 36 inches above the walking surface. The calculator asks about each of these locations per window and flags tempered required by citing the specific R308.4 subsection.

Insert vs. full-frame window replacement — which should I pick?

Insert (also called pocket or block-frame) leaves the existing window frame in place and slides a new unit inside the existing jambs. Math runs on the inside-frame dimension; no nail fin, no new flashing. Faster, less disruptive, lower cost — but you lose roughly 0.5 to 1 inch of glass area per side and you cannot inspect or repair flashing behind the old frame. Full-frame tears out to the studs, installs a new window with an integral nailing fin, and lets you redo the flashing per ASTM E2112. Math runs on the rough opening. Slower and more expensive, but the only path that resolves rot, water intrusion, or aging WRB issues. New construction is the same math as full-frame but with a continuous integrated WRB and sill pan from the start — used in additions and gut remodels.

What U-factor and SHGC do I need for my climate zone?

Per 2021 IECC Table R402.1.3: Zones 1-2: U ≤ 0.40, SHGC ≤ 0.25. Zone 3: U ≤ 0.30, SHGC ≤ 0.25. Zone 4 except Marine: U ≤ 0.30, SHGC ≤ 0.40. Zone 4 Marine and Zones 5-8: U ≤ 0.30, SHGC not required. 2024 IECC tightens U-factor in cold zones — Zones 5 / Marine-4 and Zone 6 move to U ≤ 0.28; Zones 7-8 move to U ≤ 0.27. Pulling a permit triggers compliance with the IECC version in effect on the permit date, regardless of the original window. Area-weighted averaging across multiple fenestration products is permitted per IECC R402.3.1. The NFRC label on each window is the only rating that satisfies inspection — center-of-glass U-factors from marketing materials are not the whole-window value.

Are new windows tax-deductible in 2026?

No. The Federal §25C Energy Efficient Home Improvement Credit was terminated by Pub. L. 119-21 (One Big Beautiful Bill Act, signed July 4, 2025) for property placed in service after December 31, 2025. Through Dec 31, 2025, §25C provided 30% of cost up to $600/year for windows meeting ENERGY STAR Most Efficient certification, with a $1,200/yr aggregate envelope cap. The Inflation Reduction Act had previously extended §25C through 2032; OBBBA cut it short. State and utility rebates may still apply — check your local utility and state energy office. The calculator displays §25C as expired by default; toggle the "install before Jan 1 2026" checkbox to see the historical credit calculation for pre-sunset installs.

How do I measure a window for replacement?

Three measurements per dimension — use the smallest. For width: measure at the top, middle, and bottom of the opening. For height: measure at the left, center, and right. Older homes often have racked or settled openings; the smallest measurement is what the new window has to fit. For insert / pocket replacement, measure inside the existing frame jamb-to-jamb and sill-to-head. For full-frame replacement, measure the planned rough opening AFTER tear-out — the existing trim and casing hide the actual stud opening, which is usually 0.5-1 inch wider in each direction. Andersen, Pella, Marvin, Milgard, and JELD-WEN all publish dedicated insert vs. full-frame sizing tables; pull the right one for your install path.

Andersen vs. Pella vs. Marvin vs. Milgard vs. JELD-WEN — quick orientation?

Andersen 400 Series uses a composite Fibrex frame with a deep custom catalog and a vinyl-clad / wood-interior tilt-wash double-hung that has been the volume leader for decades. Pella 250 Series is vinyl with hidden screens on hung and slider; the multi-chambered fully-welded frame is rated 52% stronger than standard vinyl per Pella's published Architectural Design Manual. Marvin Elevate uses an Ultrex fiberglass exterior with a wood interior — a mid-tier upgrade from vinyl with thinner sightlines and better long-term dimensional stability. Milgard Tuscany V400 is vinyl with the SmartTouch lock (now owned by MITER Brands). JELD-WEN V-2500 is vinyl with broad Lowe's distribution; W-2500 is the clad-wood line in the same SKU family. The calculator does not editorialize quality beyond published specs — use the dropdown for the product line you're actually pricing.

Why isn't my window a standard size?

Standard sizes are in-stock at the manufacturer and ship in 2-3 weeks. Custom sizes are special-order in 1/8" increments and add 4-6 weeks lead time depending on the manufacturer. All five primary brands (Andersen Custom, Pella Special Sizes, Marvin made-to-order, Milgard, JELD-WEN) offer custom sizing. For replacements, the existing rough opening dictates the order — measure carefully and order the closest standard size below your rough opening, then shim out the difference (typical shim allowance is 1/4 to 1/2 inch per side). Older homes with non-standard openings often need custom sizes; new construction can almost always use a standard size by sizing the rough opening to the catalog.

Window Calculator (Free) — Egress, U-Factor & Materials

How to Use This Calculator

Set project context: climate zone (1-8 + Marine-4), IECC code year (2021 default, 2024 toggle), and any stretch code overlay (CA T24, MA Stretch, NY ECCC, WA WSEC).
Toggle project-wide flags: permit pulled (triggers IECC compliance check), built before 1978 (EPA RRP applies), HVHZ designation (impact glass required), install date before Jan 1 2026 (§25C eligibility).
For each window: pick type (double-hung, single-hung, casement, awning, slider, picture, bay/bow/garden, special-shape), install path (insert / full-frame / new construction), manufacturer, frame material, and glass package.
Enter rough opening width and height in inches, plus sill height above finished floor (for R310 sill-height check on bedrooms).
Tag location flags per window: bedroom (EERO required), grade-floor / basement (5.0 sq ft NCO threshold instead of 5.7), within 24" of a door (R308.4.2), adjacent to tub/shower (R308.4.5), on a stair/ramp (R308.4.6).
Optional: override the default U-factor and SHGC with the actual NFRC certified values from each window's label. Calculator defaults to typical mid-tier values per glass package — explicit NFRC values are required for permit-ready compliance.
Add more windows (up to 20 per project). Click Calculate: per-window row shows NCO, egress verdict, safety-glazing flags, U/SHGC, install path, and any HVHZ issues. Project totals show area-weighted U-factor and SHGC, IECC pass/fail verdict, full materials list, and §25C status.

Why The Per-Window Row Matters

Window code compliance is per-opening, not per-project. A house can have a perfectly compliant IECC weighted U-factor while failing a single bedroom's IRC R310 egress requirement — and the bedroom failure stops the certificate of occupancy. This calculator surfaces a row-level verdict for every window: net clear opening in sq ft (with the actual height and width), egress pass/fail with the specific reason cited, safety glazing triggers naming the R308.4 subsection, HVHZ impact-glass mismatch, and the per-opening flashing materials. Project totals then aggregate everything. The math approach mirrors how a building official actually reads a plan-review submittal: per-opening first, project-summed second. NCO formulas in this calculator are approximate — Andersen, Pella, Marvin, Milgard, and JELD-WEN all publish per-call-size NCO tables; verify against the manufacturer's spec sheet before placing the order.

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