Resource
Window terms in plain English
Window quotes are dense with ratings, methods, and code language. This page translates the vocabulary a Tuscaloosa homeowner is likely to meet, roughly in the order a project runs into each term.
- NFRC label
- The performance sticker on every certified window, issued under the National Fenestration Rating Council program. It carries U-factor, Solar Heat Gain Coefficient, visible transmittance, and air leakage, and it is the only way to compare products across brands on equal terms. Record the numbers before peeling the label off.
- Solar Heat Gain Coefficient (SHGC)
- The fraction of the sun's heat that passes through a window, from 0 to 1. In a cooling-dominated climate like Tuscaloosa's this is the number that matters most, because summer heat gain drives the annual bill. Roughly 0.25 or lower is a strong target on sun-exposed walls.
- U-factor
- How readily heat conducts through the whole window assembly, typically 0.20 to 0.60. Lower insulates better. It is the number northern buyers optimize; in Alabama it ranks behind SHGC because our indoor-outdoor temperature differences are modest compared with a northern winter.
- Low-E coating
- A microscopically thin metallic layer on the glass that reflects infrared energy while letting visible light pass. Coatings are tuned differently for heating and cooling climates, and a cooling-climate Low-E is what belongs on a house here.
- Argon fill
- Inert gas sealed between the panes in place of air. It conducts heat more slowly than air, improving the U-factor at modest cost. Often bundled into a standard glass package rather than priced separately.
- Warm-edge spacer
- The perimeter component holding the panes apart, made from low-conductivity material instead of plain aluminum. It cuts the thermal bridge at the glass edge, which reduces the edge condensation that shows up during humid shoulder seasons here.
- Insulated glass unit (IGU)
- The sealed sandwich of two or three panes with a spacer, desiccant, and gas fill between them. It is a single manufactured assembly, which is why a failed seal cannot be repaired in place and the unit has to be replaced.
- Seal failure
- When the perimeter seal on an insulated glass unit breaks down, humid air enters, the desiccant saturates, and permanent haze forms between the panes. The tell is a fog you cannot wipe off from either side. It is the most common reason a twenty-year-old house needs windows.
- Insert replacement
- Also called a pocket replacement. The old sash comes out and a new window is fitted inside the existing frame, leaving interior and exterior trim undisturbed. Faster and cheaper, and correct whenever the frame is square and sound.
- Full-frame replacement
- Removal of the entire window down to the rough opening so the sill, jambs, framing, and flashing can be inspected and renewed. The right method when there is rot, an out-of-square opening, or a size change, which describes many pre-1940 homes here.
- Rough opening
- The framed hole in the wall a window sits in, sized slightly larger than the unit to allow shimming. It is only exposed during full-frame or new-construction work, which is the only time the framing around it can be checked.
- Nailing fin
- The flange around a new-construction window that fastens to the wall sheathing and tucks under the water-resistive barrier and flashing. It gives the best water management available, and it requires an open wall, which is why these units belong to additions, rebuilds, and re-siding projects.
- Sill pan flashing
- A formed or applied barrier under the window that catches any water reaching the sill and directs it back out. In a climate with this much wind-driven rain it is one of the highest-value details in the whole installation, and it is invisible once the trim goes on.
- Water-resistive barrier
- The house wrap or equivalent layer behind the cladding that sheds water reaching the wall. Window flashing has to integrate with it in shingle-lapped fashion, upper layers over lower, so water runs down and out rather than in.
- Design Pressure (DP) rating
- How much wind load a window assembly withstands before structural failure, in pounds per square foot, covering both inward and outward pressure. It rates the whole assembly rather than the glass alone.
- Laminated glass
- Two panes bonded to a tough plastic interlayer, the same construction as a car windshield. When struck, the fragments stay adhered and the assembly generally stays in the opening. It is the construction behind impact resistance, and it also improves security and sound.
- Tempered glass
- Heat-treated safety glass that breaks into blunt granules rather than shards. Stronger than annealed glass and required by code in certain locations such as near doors and in bathrooms, but unlike laminated glass it leaves the opening entirely when it breaks.
- Double-hung window
- A window with two sashes that both slide vertically, usually tilting in for cleaning. The traditional style on this region's older homes. Because only half the height opens at once, it is often the style that fails egress clear-opening math.
- Casement window
- A window hinged at the side that cranks open like a door, swinging the whole sash clear of the opening. That full opening makes it the usual solution when a wall is too narrow to reach egress requirements any other way, and it seals tightly when closed.
- Single-hung window
- Like a double-hung but only the bottom sash moves. Slightly cheaper and slightly tighter, since the fixed upper sash has no operating gaps, and common on builder-grade installations in newer subdivisions.
- Egress window
- A window sized for emergency escape and rescue: minimum 5.7 square feet of clear opening, at least 20 inches wide and 24 inches high, with a sill no higher than 44 inches. Required in sleeping rooms and finished basements, and what makes a room a legal, appraisable bedroom.
- Clear opening
- The actual unobstructed space a person can pass through with the window fully open, as opposed to the rough opening, frame size, or glass area. It is the measurement egress code uses, and confusing it with the others is the most common reason an egress project fails.
- Window well
- The excavated area outside a below-grade egress window, retained by a corrugated or masonry wall. Code sets minimum dimensions, and in this climate the gravel base and drainage matter as much, since an undrained well collects rain and delivers it to the opening.
- Bay window
- A projecting assembly of three units, an angled pair flanking a larger center window, creating a shelf or seat inside. The small roof over the projection is the detail that decides whether it lasts, because it has to be flashed into the wall above and pitched to drain.
- Bow window
- A projecting assembly of four or more equal units set in a gentle arc, wider and softer in appearance than a bay. It spans more wall and admits light across a broader sweep, with the same support and flashing demands as a bay.
- Muntin
- The bar dividing panes within a sash, creating the divided-light pattern on traditional windows. Historic district review pays attention to whether muntins have real depth or are flat grilles sandwiched inside the glass, because the shadow line is what reads from the street.
- Weight-and-pulley sash
- The original operating mechanism on pre-war double-hungs: cast iron weights in hidden pockets, connected by cord over pulleys, counterbalancing the sash. Broken cords are why so many old windows are painted shut or propped with a stick, and re-roping is a standard part of restoration.
- Weatherstripping
- Sealing material closing the gaps around an operating sash. On a historic window it addresses air leakage, which is where most of the comfort problem lives, and it is why a restored and weatherstripped old sash performs far better than its reputation.
- Thermal break
- A non-conductive separation between the inside and outside of a metal frame. Without one, an aluminum window conducts heat straight through the wall, which is exactly what the original windows on this area's postwar ranches do.
- Certificate of appropriateness
- The approval a preservation commission issues for exterior work in a designated historic district. Window projects inside the Original City, Druid City, and Pinehurst areas need it before ordering anything, and it runs on the commission's meeting calendar rather than on demand.
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