Windows & Exterior Doors

Table 1 maps the parts to the components. Subsections that cover only windows or only doors carry an Applies to tag; untagged subsections apply to both. An Informs tag marks the subsections behind each decision above.

1 · Heat: whole-window U and the code routes

Whole-window U is a parallel-path problem

Informs D2

NFRC 100 rates the whole product by area-weighting three zones of very different conductance. It is the same arithmetic as a stud wall (Insulation · Parallel paths), and the uninsulated path dominates in the same way.

cg center of glass · eg edge of glass, a 2½ in band degraded by the spacer · f frame and sash

the window's U is the area-weighted average of its glass center, glass edge and frame.

The reference unit is 3 ft × 5 ft with a 2¼ in frame face. Its zones are 9.29 sf of center glass, 2.85 sf of edge and 2.86 sf of frame, so the frame is 19.1% of the area whatever it is made of (Figure 1). What varies is what each zone is made of. Table 2 and Figure 2 compare five constructions.

Table 3 compares the common frame materials:

Two cautions on reading the numbers. A quoted "U-factor" that turns out to be center-of-glass describes the 9.29 sf that was never the problem; the whole-window NFRC rating at the actual size is the figure that counts. And the polymer-frame result sits right on the 0.27 threshold, so a margin under 0.02 is within the uncertainty of class-typical inputs.

Frame share, and with it U, varies with unit size

The frame is a perimeter band, so its share of the area falls as the unit grows. An operable sash puts two frames in series, so a casement runs a higher U than a fixed lite of the same outside dimensions. Table 4 holds materials constant.

A bathroom or stair window can miss 0.27 with glass that passes everywhere else. The mandatory 0.40 ceiling is an area-weighted average over all fenestration, so large units carry small ones.

What the glazing is worth in the energy balance

Glazing is often the largest single row in a house of this era's envelope UA, on a small share of its area (Insulation · Envelope UA by component). Replacing it changes annual energy modestly and the design load more.

Per 100 sf of glazing going from U 0.80 to 0.27, the reference case saves about 266 kWh/yr (about $107) and about 1,900 Btu/h of design load. Annual savings scale with degree-days and price and inversely with COP. A saving of this size does not by itself repay a window replacement. The design-load effect does more work: it moves heat pump selection and widens the outdoor-temperature range over which low-temperature radiant supply water stays sufficient (HVAC · Design heating load).

Condensation forms on the coldest interior surface

Figure 3 shows the effect (values in Table 5). At a whole-window U of 0.80 the average surface falls below the dew point of 70 °F, 50% RH air at about 34 °F outdoors. At 0.40 and below it stays clear. These are area averages: a non-broken aluminum frame runs far colder than the glass because the frame, not the glass, is the heat path, and it condenses first. NFRC 500 rates condensation resistance (CR) for this reason, and where a manufacturer lists it, CR is the figure to compare between frames. Frames that run wet on a cold morning while the glass stays dry confirm the frame class at no cost, and persistent condensation at the sill is a mold and finish-failure path that the energy arithmetic does not show.

Where no forced-air stream washes across the glass (a radiant system, for example), nothing masks a marginal window; a cold glass surface is felt as radiant asymmetry from several feet away (HVAC · Radiant comfort). Interior humidity control is in the same guide.

Title 24 routes for U-factor

Informs D3

The mandatory tier always applies; prescriptive or performance is chosen on top of it. The code values change by climate zone, so the parcel's zone decides which values apply. Figure 4 traces the route a replacement takes, and Table 6 gives the sections and values.

Alterations that add fenestration area must also meet the area limits of §150.1(c)3A: total fenestration at most 20% of conditioned floor area, west-facing at most 5%. Adding up to 75 sf is exempt from these limits. Opening sizes and the added area go on the compliance document.

2 · Sun: the glass sets a fraction; geometry sets what it is applied to

SHGC is a property of the glass; incident flux is a property of the face

At latitude 37.4° N the noon sun is 29.2° high in December, 52.6° at the equinox and 76.0° in June. On a south face γ is zero at noon, so cos θ collapses to cos α: the geometry that maximizes winter gain minimizes summer gain with no device at all. A west face does the opposite. Table 7 and Figure 5 give the peak cases.

One SHGC limit does different work on each face

The prescriptive limit of 0.23 is calibrated to the west case. The code applies one number to four orientations, and the effect on each is different. For 100 sf of south glass, SHGC 0.35 instead of 0.23 admits 3,309 Btu/h more at December noon and 1,262 Btu/h more at June noon (about 0.11 ton of cooling). In a heating-dominated mild climate the December term is the one that matters, and on a south face the low-SHGC glass withholds more useful winter gain than it excludes summer gain.

That conclusion depends on the balance of heating and cooling. It inverts in a cooling-dominated climate or where internal gains make December sun unwelcome, and it disappears where the prescriptive path has no SHGC requirement at all (climate zones 1, 3, 5 and 16). On a west face the same number is correct.

Overhang shading depends on projection, height and sun altitude

Table 8 and Figure 6 apply this to a 5 ft window. An 18 in eave one foot above the head fully shades a 5 ft south window at June noon and leaves the window unshaded at December noon: close to the geometric ideal for the orientation. An overhang does nothing at the low sun angles early and late in the day, when γ is large. Title 24 credits overhangs in the performance method through the projection factor (overhang projection divided by the distance from the overhang to the window sill).

Visible transmittance and solar gain are rated separately

Spectrally selective coatings buy visible transmittance (VT) at a given SHGC. The ratio VT/SHGC, the light-to-solar-gain ratio (LSG), is the way to compare them; both numbers are on the NFRC label. Daylight quality, glare and room-by-room targets belong to Lighting · Daylighting. The code's daylight minimum is a glass-area rule, in Part 5.

3 · Sound: the glazing governs the facade until the wall takes over

Soundproofing owns the theory used here: STC vs. OITC, mass law, mass-air-mass resonance, coincidence, damping, parallel paths and leaks. This part applies it to glazing and states only what is specific to an opening. For traffic and rail, OITC is the rating that compares glazing: the STC reference spectrum rolls off below 125 Hz and flatters a window by 5–10 points. How much reduction is needed depends on exposure: level falls about 3 dB per doubling of distance from a busy road (line source) and about 6 dB from a single rail or point source, so a house set well back may need little beyond a good seal, and one close to the source needs the full treatment below.

How glazing and wall share the transmitted sound

Sound crosses a wall through its paths in parallel, weighted by area, so a small area of weak glass can carry most of the transmitted energy. Composite loss comes from the area-weighted transmission coefficient (Soundproofing · Composite loss). Table 9 works the cases.

With a wall at STC 39 and 15% glass, the existing glazing (STC 28) carries 69% of the transmitted energy. Raising the glazing to STC 40 moves composite loss by about 4.5 dB and drops the glazing's share to about 12%: the wall then limits, and 5 more STC points of glazing return only 0.4 dB. With the wall at STC 50 the same 5 points return 2.5 dB. The diminishing return belongs to the pair, not to either element.

What a sealed glazing unit can and cannot do

Informs D2

The resonance of a sealed unit depends only on lite mass and cavity width. Low-E coatings, gas fills and warm-edge spacers do not move it. Lamination does not move it either; it damps the coincidence dip. Equal lites put both dips at the same frequency; unequal lites separate them. Table 10 and Figure 7 compare six build-ups.

The useful question is what share of the source spectrum lies above f₀, where the unit works as a true double leaf. Taking the dominant band as 31–250 Hz and spreading it evenly by log frequency, none of it lies above 283 Hz, about 22% lies above 159 Hz, and about 62% lies above 69 Hz. A sealed unit is limited to about 20 mm of cavity by seal life, so the cavity cannot be widened to reach that range.

Table 11 lists the variables on which the two goals pull apart. The gap in code units is small. The acoustic laminate (build-up E) computes to U 0.30 in a polymer frame, 0.29 with a lower-emissivity coating, and 0.40 in thermally broken aluminum. That misses 0.27 by 0.02–0.03 in polymer. These margins are within the ±0.01–0.02 uncertainty of class-typical inputs; only the product's NFRC rating at its actual size settles whether a unit clears 0.27 or 0.40. The consequence is that the acoustically preferred unit needs a code route above 0.27 (Part 1), and a slim thermally broken aluminum frame uses that route on its own before any acoustic requirement is added.

Laminated glass that is required for safety glazing anyway (Part 5) delivers the damping at little extra cost; the two requirements arise from unrelated parts of the code.

Secondary glazing: an independent inner sash lowers resonance

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Informs D2

An independent inner sash, 50–150 mm inboard of the retained unit, is the double-stud wall of Soundproofing · Double-leaf resonance applied to an opening. Its resonance falls below the source band (Table 12):

Gap width is the dominant acoustic variable and nearly irrelevant thermally: the resistance of a vertical air space stops rising once convection sets in (about R-0.90 at 50 mm, R-1.02 at 100 mm, R-1.05 at 150 mm). Center-of-glass U drops from 0.49 to about 0.32. The assembly is field-assembled, not a rated fenestration product, so Title 24 gives it default values and it does not serve as a route to the prescriptive limit.

The retained unit gets colder

Figure 8 shows the section. Resistance added on the inboard side moves the whole temperature gradient outward. The retained unit's cavity-side face runs colder than it did alone, and any moisture in the cavity condenses there (Table 13).

Other consequences, none acoustic: both sashes must open from inside without keys or tools wherever the opening serves as an escape opening, and the net clear opening is the smaller of the two (Part 5); there are two sashes to open and four glass surfaces to clean; the inner frame consumes 50–150 mm of reveal and reads as a second window. The method is fully reversible and can be tested on a single room, and it is the only way to improve an opening without replacing the unit, which avoids the glass-area cost of an insert (Part 4).

Operator type, seals and leakage also govern delivered sound: Part 4. Door leaves, thresholds and sliding-door stiles: Part 7.

4 · Air and water: leaks are decided by seals and by the perimeter

Operator type sets the seal type, which governs leakage and part of the sound

Operators differ in one way that matters here: compression seal against sliding seal. A casement, awning or tilt-turn sash closes by drawing the sash against a continuous gasket with a multi-point lock. A slider or hung sash has to pass the seal, so it uses brush or fin-pile weatherstripping that cannot compress, and it degrades with use. The gasket that stops air also stops sound. Table 14 compares the common operators.

A slider and a casement of otherwise identical construction differ by roughly 2–4 OITC points. A leaking sash also caps delivered performance whatever the glass is (Soundproofing · Leaks).

Title 24 caps manufactured fenestration and residential exterior doors at 0.3 cfm/ft² at 75 Pa (§110.6(a)1); any NAFS-certified product satisfies it.

Against the whole house (Table 15), window leakage is small. Windows are a small share of whole-house leakage even at the code maximum (the ceiling plane dominates, Insulation · Air transport), so new glazing is not an air-sealing measure. A worn aluminum slider is the exception, and the difference between a worn slider and a good casement is large relative to the windows and small relative to the house.

Water is controlled at the perimeter joint

Water intrusion at windows is mostly an installation failure. The unit is tested to NAFS water penetration at 15% of its design pressure, at least 140 Pa (2.9 psf); a PG30 unit is water-tested at about 4.5 psf, the pressure of a wind of about 42 mph (p = 0.00256 V²). The joint between unit and wall is tested by the weather.

Three mechanisms drive water through an opening: gravity, capillarity and air-pressure difference. Sealant addresses all three temporarily and none durably. A correctly built opening handles them with geometry:

• A sloped, back-dammed sill pan that collects anything passing the unit and drains it outward onto the drainage plane. This is the component most often omitted in retrofit work.
• Shingle-lapped flashing: head over the weather barrier, jambs over the sill pan, everything lapping downhill. Lapping is geometry and does not degrade under UV.
• A continuous air seal at the interior, which removes the pressure difference that drives water inward (Insulation · Air barrier).

Figure 9 shows the three in section.

Installing into a wall with nail-fin originals

WindowsDoors

Informs D1

A nail-fin unit is lapped into the building paper behind the stucco, which is how most California tract houses of the 1980s to 2000s were built. The head and jamb flashing cannot be renewed without removing stucco. Any replacement that leaves the stucco in place therefore keeps the original flashing in whatever condition it is in, with sealant at the new perimeter as the only added water control. That is not automatically a defect: a drainage plane that has gone two or three decades without a leak is evidence about itself, and a mild climate with modest wind-driven rain is a forgiving environment. It is a condition with a service life. Under siding or veneer the exterior can be opened and flashed without patching, so the choice turns on cost and finish rather than access. Table 16 and Figure 10 compare the installation methods.

The insert gives up about 1¾ in of clear dimension per side to the retained frame (Table 17):

Two consequences follow from that loss. Daylight: the code's 8% glass-to-floor-area minimum (Part 5) is a glass-area rule, so a room at 8.5% before an insert is at 7.2% after a 15% reduction. Escape openings: see Part 5. Where the new glazing is near the wall's own rating, the two methods are acoustically equivalent: a smaller aperture transmits less, the larger remaining wall transmits more, and the composite moves by well under 0.1 dB. The choice is then decided on daylight, egress and water management.

Doors have their own sill and threshold conditions: Part 7.

5 · Safety and structure: where code compliance and adequacy come apart

Two unrelated codes govern an opening. Title 24 Part 6 (energy) covers U, SHGC and leakage. The California Residential Code (CRC) covers escape, fall protection, safety glazing, light and ventilation, wind rating and the garage separation. A unit can satisfy one and fail the other, and one failure in replacement work, losing an escape opening to a smaller unit, is invisible to the energy calculation.

Escape openings (CRC R310)

WindowsDoors

Informs D1 D4

Every sleeping room below the fourth story needs at least one operable emergency escape and rescue opening (EERO), measured on the net clear opening: the hole a body passes through with the sash fully open. It is not the rough opening or the glass. Table 18 lists the four requirements.

Figure 11 shows the measurement; Table 19 and Figure 12 apply the formulas. A slider needs a rough opening at least 46 in wide to reach the 20 in minimum at any height, and a single-hung needs roughly 54 in of height for 24 in of clear opening. The same rough opening as a casement yields about 75% more escape area than a slider. A fixed lite cannot serve as the escape opening. Awning windows rarely satisfy the height and area together.

The replacement exemption, and what resizing does to it

The CRC exempts replacement windows from the dimensional and sill-height requirements when the replacement is the manufacturer's largest standard size that fits the existing frame or rough opening, has the same operating style or one with equal or greater opening area, and is not part of a change of occupancy. It still requires the opening to be free of obstruction and openable from inside without keys, tools or special knowledge. How the exemption behaves in each case:

• Insert into the retained frame. Exempt. A 48 × 48 slider's net clear opening falls from 6.49 to 5.48 sf and its width to 19.25 in: legal, a permanent reduction, and nothing in the inspection record shows it.
• Full-frame into the existing rough opening. Also exempt, with a larger reference opening. The provision contemplates changing operating style where the new style gives equal or greater area, and a casement in the same rough opening recovers most of the loss.
• Enlarged opening. Not exempt. A resized opening is new construction at that location, and the full requirements of the table above apply on their merits.

Window fall protection (R312.2)

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Where the sill of an operable window is less than 24 in above the finished floor and the opening is more than 72 in above the exterior grade, one of three must hold: the opening does not pass a 4 in sphere at its largest opening, or a fall-prevention device to ASTM F2090, or a window opening control device, also to ASTM F2090. The test is a conjunction, which is why it bites on second-floor rooms with low sills. F2090 devices include an emergency escape release so that fall protection cannot defeat R310. A screw through a slider track or a generic sash limiter is neither compliant nor safe. Figure 13 shows when the rule is engaged.

Safety glazing (R308.4)

Table 20 lists the hazardous locations this scope engages.

Laminated glass satisfies R308 and supplies the coincidence damping of Part 3. Unlike tempered glass it also stays in the opening when broken.

Natural light and ventilation (R303.1)

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Habitable rooms need glazing of at least 8% of floor area for natural light and openable area of at least 4% for ventilation. A whole-dwelling mechanical ventilation system that meets §150.0(o), such as an ERV, can discharge the ventilation half. Nothing mechanical discharges the light half, which is why a retrofit that removes 12–16% of the glass area in every opening (Part 4) erodes the margin.

Wind rating: PG, DP and window class

CRC R612 requires exterior windows and doors to be tested and labeled to NAFS and to resist the site's design wind pressure. Design pressure (DP) reports uniform-load deflection only. A performance grade (PG) is awarded only when the product passes every NAFS requirement at that pressure: operating force, air leakage, water penetration, uniform load deflection and structural load at 1.5 times design pressure, and forced entry. Required pressures for a two-story house in normal exposure are modest, and readily available products exceed them, so the more useful question is class rather than grade. LC and CW class products carry heavier sections and retain their seals longer than R class at the same PG, and seal retention is what a 30-year service life consumes.

Fire exposure

• Wildfire zones. In a Fire Hazard Severity Zone, CRC Chapter 7A requires tempered or multi-layer glazing, and §150.0(q) grants a U-factor exception. Most suburban parcels are outside these zones; the state Fire Hazard Severity Zone map shows a parcel's status.
• Property-line setbacks. Exterior walls closer than 5 ft to the property line must be fire-resistance rated, and openings are not allowed within 3 ft and are area-limited between 3 and 5 ft (CRC Table R302.1(1)). Side setbacks in tract housing are often about 5 ft, so side walls commonly fall in or near this range, and new or enlarged openings on them are affected. The table and any local amendments govern a resized side-wall opening (Verify).

6 · Reframing an opening: gravity, lateral, geometry and code all change

Framing owns the load path, header sizing and braced-wall rules. This part states what an opening in an exterior wall adds to those problems, and what the energy and life-safety codes add on top. Widening or adding an opening changes four things at once.

Gravity: exterior walls under clear-span trusses carry the roof

Informs D4

Engineered trusses clear-span to the exterior walls and deliver the roof load there, so the walls that contain the glazing are the walls carrying the roof. Interior walls generally do not (Framing · Which walls are structural). An exterior header therefore carries a higher line load than an interior bearing wall in the same house, and the ground-floor header also carries the second floor.

The bending demand grows with the square of the span, so widening is expensive in depth. In the reference case, widening an opening from 6 ft to 10 ft (design spans 6.5 and 10.5 ft) multiplies the moment by 2.6 and, at the same member width, calls for about 1.6 times the depth. Where a girder truss lands at the opening, its point load can double the required section modulus (Framing · Reference case).

Head height and strength both limit the header

Informs D4

the header, plus its plate, has to fit between the top of the opening and the floor framing above.

Figure 14 shows the geometry; Table 21 and Figure 15 apply the formula. Common LVL depths are 9½, 11⅞, 14, 16 and 18 in. Under an 8 ft ceiling the depth available over an 80 in head is enough for an 11⅞ in member but not a 14 in one, so a wide opening in an 8 ft wall can be limited by room above the head before the member runs out of strength. Under 9 and 10 ft ceilings the constraint relaxes for ordinary spans.

Lateral: opening width removes braced-wall length

Informs D4

Exterior walls of this vintage are braced wall panels until shown otherwise. In the same reference case, widening a 6 ft opening to 10 ft in a 15 ft wall segment cuts full-height sheathing from 9 ft to 5 ft, a 44% loss, and each jack stud pair consumes about 3 in of wall length. Whether that matters depends on the wall's classification and the bracing arithmetic of Framing · Lateral. A gravity solution does not resolve a braced-panel deficit. Wall classification precedes any decision about an opening in it.

Code status of a resized opening

Informs D4

• Escape. The replacement exemption does not apply to a resized opening, so full R310 applies to a sleeping room (Part 5).
• Energy. Added fenestration area triggers the area limits of §150.1(c)3A (Part 1): total glazing at most 20% of floor area, west-facing at most 5%, with up to 75 sf of added area exempt. Headroom is 20% less the existing glazing-to-floor ratio: a house at 15% can add 5% of its floor area, 50 sf per 1,000 sf, before the limit binds.
• Safety glazing. An opening taken to floor level engages R308.4.3 (Part 5).
• Permit. Structural work in an exterior wall needs a building permit, and removing or shortening a braced wall panel is among the triggers for an engineer's stamp (Framing · The engineer threshold).
• Exterior finish. The stucco is cut at a resized opening, so an exterior flashing detail can be built in full there, unlike an insert (Part 4). The changed exterior is also what homeowner-association covenants usually regulate.

7 · Exterior doors: what changes from the window case

Everything in Parts 1–6 about glazing and frames applies to a glazed door: the glass specification is a window's. This part covers what is different about a door as an assembly. Door-specific code is here, and the house-specific entries (which doors, which glass) belong in the House Project Guide.

What differs from a window

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• Seal length per area is about the same as a window's (0.97 ft/sf for a 3 ft × 6 ft 8 in door, 0.90 for a 4 × 5 ft window, 1.07 for a 3 × 5 ft window). What differs is the bottom edge: the seal there is a sweep dragging over a threshold, not a compressed gasket, and it wears with use.
• The threshold is a continuous thermal bridge. It runs metal from outside to inside and bears on the slab edge, itself an uninsulated bridge (Insulation · Slab edge). It is the coldest interior surface in the house, and the whole-door U is perimeter-dominated rather than panel-dominated.
• A leaf is large, heavy and unsupported over its height. It carries a temperature and humidity gradient across its thickness. Warp opens the seal, and on a sun-exposed face a dimensionally stable core (insulated steel, fiberglass or engineered stile-and-rail) keeps its seal better than solid timber.
• Doors are operated thousands of times and are forced. Gaskets wear, hinges sag, and security loads act on the lock and strike.

Threshold, water and landings

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Figure 16 shows the section. A door sill sees splash, standing water and foot traffic that a window sill does not. The water-management mechanisms of Part 4 apply, with the sill pan carrying more of the load: a sloped pan under the threshold that drains outward, a threshold seated on sealant, and an overhang or roof above that keeps the base dry. Opening-specific drainage at a flush or low threshold (as on multi-slide and lift-and-slide units) is the usual failure point of large glazed doors.

The floor build-up interacts with two life-safety dimensions. Raising the finished floor lowers the effective sill height of nearby escape windows (favorable against the 44 in maximum) and reduces the drop to an exterior landing (unfavorable against CRC R311.3, which allows no more than 1½ in below the threshold at the required egress door). Both are checked against the final floor assembly, including any radiant topping (Finishes · Radiant floor build-ups).

Heat, sound and security

WindowsDoors

Informs D5

Heat. Opaque doors (less than 25% glazing) have a prescriptive limit of U 0.20 in all climate zones; fire-rated swinging doors between garage and conditioned space are exempt. At 25% glazing or more a door counts as fenestration and takes the window limit, 0.27 or 0.30 depending on zone, which is an easier target. Large glazed doors are thermally easy: a patio-sized unit reaches about 0.26 on ordinary glazing because the frame fraction is small.

Sound. A door follows the mass law like anything else, but a hollow or foam-core leaf has a surface mass of roughly 3–6 kg/m² against 15–25 kg/m² for glazing, so the leaf is usually the weakest element on its wall. A solid-core 1⅜ in door with full perimeter seals is roughly STC 30–35. The threshold is the weak element at the base. For glazed patio doors the seal type decides, as in Part 4: a sliding unit has a brush-sealed meeting stile over its full height that a hinged or lift-and-slide unit does not, so a sliding door governs its wall acoustically whatever glass is in it (Figure 17).

Security. NAFS tests forced-entry resistance separately (ASTM F476 for swinging, F842 for sliding). A multi-point lock draws the leaf evenly against the gasket at three or more points, which improves security, air sealing and warp control together. Laminated glass resists entry through the glazing. Hardware, sensors and access control are in Security · Entry hardware.

Life-safety requirements for doors

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• Egress door (R311.2). At least one side-hinged exterior door, at least 32 in clear width and 78 in clear height with the door open 90°, openable from inside without key or special knowledge. A sliding door does not satisfy it.
• Landings (R311.3). A floor or landing on each side of the door, not more than 1½ in below the threshold at the required egress door.
• Safety glazing (R308.4.1, R308.4.2). All glazing in doors, and glazing beside them, is safety glazing (Part 5).

Door types compared

WindowsDoors

Informs D5

Table 23 compares the common door types on the functions that differ.

Two readings. The thermal and acoustic optima diverge for doors as they do for windows: the sliding patio door is the easiest large opening thermally and the hardest acoustically. And a hinged or lift-and-slide unit is the technically consistent choice for a large noise-facing opening, at the cost of leaf weight and hardware.

8 · Permits and documents

Informs D3

Thresholds are stated where they apply (Parts 1, 5, 6 and 7). This part covers the process around them.

• Which code. The 2025 California codes took effect 1 January 2026 and apply to permits applied for on or after that date (Insulation · Which code, which cycle).
• Permit. Replacing a window or exterior door is a regulated alteration in most jurisdictions and triggers Title 24 §150.2(b). Replacing glass only, or a sash only, in a retained frame is treated as a repair by several city forms and usually needs no permit. Practice varies; the local building department's reading decides.
• Compliance documents. The certificate of compliance (CF1R) is prepared at design and submitted with the plans. The installation certificate (CF2R-ALT) is completed by the installer and given to the owner and the inspector at final. Glazing does not generally need HERS field verification.
• Labels. The temporary NFRC label showing U, SHGC and VT stays on each unit until the inspector has seen it, with the permanent label. Removing it is a routine and avoidable failure.
• Product must match the document. A supplier substitution, such as a different coating because the specified one was unavailable, can invalidate the CF1R. A label check against the document at delivery catches it.
• Plan-check consistency. The window schedule, the CF1R fenestration table and the floor plan must agree: each opening listed with its dimensions, operator type, U-factor, SHGC, safety-glazing status, escape-opening status, and any exception area used.
• Structural scope. Where an opening is enlarged, the structural permit and engineering thresholds of Framing · The engineer threshold apply.

Where it goes wrong

1. Losing an escape opening to an insert. The replacement exemption makes it legal and nothing records it; only the net clear opening of the new unit in a sleeping room shows it (Part 5).
2. Putting good glass in a frame that cannot carry it. Low-E glass in a non-broken aluminum frame cannot reach current limits, and a center-of-glass U-factor on a quote describes the zone that was never the problem (Part 1).
3. Specifying STC for traffic or rail. OITC is the right metric. Triple glazing is not quieter: three thin equal lites add a second resonance and keep the dips coincident (Part 3).
4. Treating a prescriptive SHGC as orientation-neutral. It does different work on each face (Part 2).
5. Enclosing a failed unit behind a secondary sash, or venting the cavity indoors. Both produce permanent moisture on a surface that cannot be cleaned (Part 3).
6. Relying on sealant for water management. The sill pan, lapped flashing and interior air seal carry the load; sealant is the backup (Part 4).
7. Defeating egress with a fall-protection device or a fixed inner panel. Only F2090 devices with an escape release are compliant, and an inner sash must open from inside without tools (Part 5).
8. Assuming a resized opening inherits the replacement exemptions. Escape rules and energy area limits both attach to the new opening (Part 6).
9. Sizing a widened opening's header on interior-wall assumptions. The exterior wall under trusses carries more, head height may bind first, and the lateral question is larger than the gravity one (Part 6).
10. Removing the NFRC labels before inspection, or accepting a substitution. (Part 8)
11. Treating a sliding door as the acoustic or air-seal equal of a hinged one. Its brush-sealed stile is a continuous aperture (Part 7).

Reference

Glossary

Astragal

The member closing the gap at the meeting stiles of a pair of doors. A compression astragal seals when the leaf latches; a brush astragal does not.

Condensation resistance (CR)

An NFRC 500 rating, 0–100, of how well a product resists surface condensation. The figure to compare between frames.

EERO

Emergency escape and rescue opening, CRC R310.

Field-fabricated fenestration

Glazing assembled on site rather than as a rated product. It cannot be NFRC-rated and takes default values under Title 24 §110.6(b).

IGU

Insulating glass unit: the sealed multi-pane assembly within a sash.

LSG

Light-to-solar-gain ratio, VT ÷ SHGC.

Nail fin

An integral flange on a window frame, nailed to the sheathing and lapped into the weather barrier before the cladding goes on.

Net clear opening

The aperture a body passes through with the sash fully open. Not the rough opening, not the glass.

NAFS

AAMA/WDMA/CSA 101/I.S.2/A440, the North American Fenestration Standard referenced by CRC R612.

NFRC 100 / 200 / 400 / 500

Test procedures for U-factor, SHGC and VT, air leakage and condensation resistance.

PG, DP

Performance grade and design pressure. DP reports deflection only; PG is awarded only when every NAFS requirement is passed at that pressure.

Repair (energy code)

Glass-only or sash-only replacement in a retained frame, treated by several city forms as not an alteration.

Rough opening (RO)

The framed hole. The reference for full-frame replacement; the retained frame is the reference for an insert.

SHGC, VT

Solar heat gain coefficient and visible transmittance of the glass.

Sill pan

A sloped, back-dammed membrane or formed pan under a window or door that drains water outward onto the drainage plane.

WOCD

Window opening control device, CRC R312.2.2 / ASTM F2090, with an emergency escape release.

Z-bar

A flashing section that covers the joint between a replacement unit and a stucco wall without breaking the stucco-to-fin seal.

Formula sheet

Figure color legend

Red: deficient, or fails the stated criterionAmber: marginal or carries a caveatGreen: meets the criterionGray: existing or baselineTeal: neutral quantity, reference line or annotation; never a grade

Two figures use color for something other than a grade and say so in the caption: Figure 2 uses a teal family for the three zones and chips for code status; Figure 5 uses one fill because it plots one quantity.

Code points to confirm

These are the values in this guide that rest on a single secondary source or on a cycle that has changed. Each is marked Verify where it appears.

• The 75 sf replacement exception by climate zone in the 2025 cycle (§150.2(b)1B)
• The opaque-door limit of U 0.20 and the fire-rated garage-door exemption (Table 150.1-A)
• The CRC replacement-window exemption: section number and exact conditions in the adopted edition
• CRC R302.5.1 wording on self-closing and self-latching garage doors
• CRC Table R302.1(1) opening limits near a property line
• The installed-SHGC tolerance sometimes quoted for the 2025 cycle (not found in the sources checked; omitted from this guide)

Sources

• California Energy Commission, 2025 Building Energy Efficiency Standards: What's New for Single-Family Residential — §150.0(q) mandatory U 0.40; §150.1(c)3A prescriptive U 0.27 / 0.30 and SHGC by climate zone.
• 2025 California Energy Code (Title 24 Part 6) §110.6 — air leakage 0.3 cfm/ft² at 75 Pa, NFRC ratings and labels, field-fabricated defaults (as excerpted by GoCodeBook).
• City of Elk Grove, Residential window or skylight alteration energy form, January 2026 (2025 cycle) — exceptions, area limits, repair definition; City of Roseville, 2025 CF1R window replacement and CF2R-ALT requirement.
• City of Tustin, User guide to replace emergency escape and rescue windows — replacement-window exemption conditions as applied locally.
• 2025 California Residential Code R302, R303.1, R308.4, R310, R311.2–3, R312.2, R612; NAFS (AAMA/WDMA/CSA 101/I.S.2/A440); ASTM E283, E413, E1332, F476, F842, F2090; NFRC 100, 200, 400, 500.
• Companion guides in this set: Framing, Soundproofing, Insulation and HVAC (set v2, linked by topic); Lighting and Security (set v2) likewise; Finishes (Guide 12) is not yet written.

Set v2 draft 2d, 2026-10-23: the Security reference links to the set v2 guide (Entry hardware); the garage door rule adds California's self-latching requirement. Draft 2c, 2026-10-23: the Lighting · Daylighting reference links to the set v2 guide. Draft 2b, 2026-10-23: Insulation and HVAC references link to their set v2 guides; design-load change restated at the 35 °F design difference. Draft 2a, 2026-10-23: Framing and Soundproofing references now link to their set v2 guides. Draft 2, 2026-10-23: readability revision (collapsed derivations, four new figures, linked references, decision tags). Draft 1, 2026-10-22: rewritten as a generic theory guide from the v1 guide (archived). All values computed from one script; STC and OITC ranges and component U-factors are class-typical, not product data.

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