Two quotes arrive on your kitchen table, both for the same job, both plausible. One says full-frame replacement, the other says pocket replacement. One lists a U-factor of 0.24, the other calls the same window energy efficient. You cannot tell which deal is better without knowing the words.
That vocabulary was written for the supply chain, not for the person paying the invoice. WDMA, the Window and Door Manufacturers Association, defines fenestration as openings in the building envelope, such as windows, doors, curtain walls, and skylights.
Opening Terms: Which Rough Opening Measurement You Actually Order Against
The rough opening causes the most confusion, because it means different sizes in different trades. WDMA defines it as the opening in a wall or roof into which a window or door is installed. Knockety calls it an unfinished opening where a unit goes.
Knockety also defines a recess as a space in a wall into which another part can be fitted. That is why a window and a door in one wall get rough openings measured differently.
Three frame names you will hear constantly: WDMA defines the head as the horizontal top member, the jambs as the vertical sides, and the sill as the bottom member. The interior door measuring guide shows how those three set measurement.
| Term | Definition | Why it matters |
|---|---|---|
| Rough opening | Unfinished hole in the wall | Order against this, not the window |
| Recess | Space in a wall | Sets how deep it sits |
| Jamb | Vertical sides of the frame | Where you nail, hinges live |
| Head | Horizontal top member | Carries sash weight, flashing |
| Sill | Horizontal bottom member | Rots first, drains it |
| Brickmold | Exterior trim as casing | The outdoor trim, an upgrade |
| Finished opening and cut-out | The opening after trim, and the hole actually cut | The size you order against |
| Apron | Trim board under a stool | Covers the gap under trim |
| Miter | The angled joint between trim | Wrong angle, corner gap |
Window Terms: Double-Hung vs Casement and the Glass Inside
WDMA defines a hung window as one with vertically sliding sashes using counterbalancing devices, and a double-hung window as a hung window with two operable sashes. That is the whole difference from single-hung: how many sashes move, not price tier.
A casement window is one with sashes hinged to open from the side, next to the jambs. WDMA groups awning and hopper as a window with sashes hinged top or bottom, awning out and hopper in.
The glass side has its own vocabulary. WDMA defines airspace as the space between adjacent layers, and the spacer as the material holding it apart. The gap insulates, not the glass.
WDMA also defines a divider as a member dividing glazing into separate vision areas, and notes that muntin means the same thing.
The window glass replacement guide shows what an airspace and a spacer look like when one fails.
| Term | Definition | Why it matters |
|---|---|---|
| Double-hung | Two sliding sashes, both move | Two-way ventilation, standard |
| Single-hung | Hung window, one operable sash | Cheaper, one less leak path |
| Casement | Sashes hinged at the side | Tight seal, sheds driving rain |
| Awning and hopper | Sashes hinged top or bottom | Awning out, hopper in |
| Sash | Members that hold the glass | The moving part, leaks start |
| Balance | Device counterbalancing the sash | A bad balance causes sticking |
| Insulating glass unit, spacer, airspace | Lites sealed around a gas space held by a strip | The gap insulates, not the glass, and a failed seal fogs |
| Divider, muntin, glazing bead | A member dividing glazing, and trim holding the glass | Structural or decorative |
| Laminated glass and tempered glass | Lites bonded with polymer, or safety glass that shatters small | Stays together when broken |
| Fenestration cladding | Exterior parts covering frame | Protects the frame, visible finish |
| Weep hole | An opening that drains water | Blocked, water sits and rots |
| Slider and fixed window | Sashes sliding horizontally, or a window that never opens | Wide opening, one handle |
| Sill pan and head flashing | A flashed pan at the base, and flashing over the window | Catches what the sill misses |
| Screen | Wire mesh, keeps out insects | Not a security product |
Performance Terms: Why U-Factor and SHGC Point Opposite Ways
The Two Numbers That Point Opposite Ways
Energy terms look like alphabet soup until you learn each measures a different thing. Heat through the glass is one problem, sunlight carrying heat another, and light getting through a third. Confusing them is how a good window ends up wrong for your climate. The window energy ratings guide splits them apart.
WDMA defines air leakage as the flow of air passing through the product, and design pressure as the rating for the wind or snow load it must withstand.
WDMA defines certification as a process where a product line sample has been tested, meets requirements, and is under ongoing outside inspection. The window energy ratings guide goes deeper on what those ratings mean for you.
| Term | Definition | Why it matters |
|---|---|---|
| U-factor | Rate of heat loss through it | Lower is better, heating number |
| Solar Heat Gain Coefficient | Solar heat through the glazing | Lower for cooling, higher in winter |
| Visible Transmittance | Fraction of visible light | Higher for daylight, rated apart |
| Air leakage | Flow of air through it | Sometimes worse than the glass |
| Certification | A tested line, inspected outside | Outside testing gives it value |
| Low-E coating | A microscopic glass layer | Lets light in, blocks infrared |
| Argon fill | Inert argon gas between panes | Conducts less heat than air |
| Operating force | Force to start or hold motion | A stiff sash is hardware |
Door Terms: Swing Direction, Hardware, and the Parts That Seal
Door hardware carries the vocabulary people mix up most. A hinge is the pivot point, handing is which way the door swings, the strike the jamb plate the latch enters, the latch the bolt.
Knockety defines a transom as a decorative window above a door, weather-stripping as sealing openings from the elements, and the threshold as the part of the unit attached to the floor.
The interior door installation guide shows those parts on a real door instead of naming them in the abstract.
| Term | Definition | Why it matters |
|---|---|---|
| Prehung unit | Slab hung in its jambs | Faster install, frame squared |
| Slab | The panel alone | Only if the frame is sound |
| Hinge, pivot, latch and strike | The pivot the leaf turns on, the axis it rotates about, the bolt, and the plate | Loose hinges swing uneven |
| Mortise | A recess cut for hardware | Wrong depth fails the fit |
| Bevel, handing, swing direction | The angled edge on a slab, which way it swings, and inward or outward | Bevel must match the frame |
| Casing | Trim covering the jamb gap | A different profile than window |
| Transom | A window above a door | Often decorative, not egress |
| Weatherstripping | Sealing openings from elements | Cheapest draft fix, often enough |
| Threshold or sill | The part on the floor | Where water collects, decides rot |
| Reveal | How far the frame sits back from the wall | Sets how deep the door sits |
Replacement Terms: What Each Method Costs You
Now the vocabulary that decides how much of your house gets torn up. A full-frame replacement removes the entire unit, frame and sill included. A pocket replacement installs a new sash into the old frame.
Full-frame replacement gives the installer access to the rough opening, so the sill can be flashed and drained, the frame checked for rot, and gaps insulated. Pocket cannot reach that, and is right when the frame is sound.
Quotes are written per unit and per opening, which differ, so the unit count tells you how many pieces you pay for. The interior door measuring guide shows how slab size, unit size, and rough opening stack up.
The rest is what gets added to the number. Flashing diverts water away from the opening, and labor separates a product quote from an installed one.
A standard residential opening runs roughly $150 to $1,200 for the unit, with labor running $100 to $300 per window and $150 to $400 per door. The window and door installation cost guide breaks those line items out
| Term | Definition | Why it matters |
|---|---|---|
| Full-frame replacement | Whole unit removed with frame | Lets the installer flash and inspect |
| Pocket replacement | New sash into the old frame | Faster, cheaper, leaves rot |
| Per unit and per opening | Pricing counted by pieces, or by holes in the wall | Three units, triple the product |
| Flashing, sealant, labor | A strip that diverts water, a compound that fills the joint, and the install work | The detail that keeps water out |
| Rough opening | The unfinished framed opening | Order against this, not the window |
| New construction | Unit built into the wall | No demolition, new builds only |
The Five Term Distinctions That Change What You Pay
These five most reliably change the number on the quote.
What is a good U-factor? At or below 0.30 is a reasonable target, below 0.20 is strong for a cold climate, and anything above 0.35 in a heating region is worth questioning. It depends on your climate zone and frame, which is why the regional ENERGY STAR label beats one number.
Here is the short version of each one.
Full-frame or pocket replacement? Full-frame takes out the entire unit, frame and sill included, so the opening can be inspected, flashed, and insulated. Pocket installs a new sash into the frame already there. Full-frame costs more but fixes what is wrong.
These next two come up on every door quote.
Do I need tempered glass? In most US residential codes, yes, in all doors and in windows within 24 inches of a bathing fixture, plus many stair and floor-level openings. You will see it on every patio door lite. It is a safety requirement, and a quote that omits it is suspect.
The third one trips up bedroom buyers.
What is egress? Egress is code terminology for the means of escape from a room, and the window requirements are specific: minimum clear opening size, minimum sill height, and operable without tools from inside. Bedrooms and basements are where you hit it most, and a window too small stops a sale.
The last one trips up shoppers reading a spec sheet.
What does Low-E mean? Low emissivity means the glass surface has a microscopically thin coating that reflects infrared heat while letting visible light through. It keeps heat outside in summer and warmth inside in winter. Low-E is an energy treatment, tempered glass a safety one, and one pane can have both.
Those five questions come up in nearly every window purchase.
Next step: get the unit and the install priced separately. The double-hung versus casement comparison settles which operation style you want before anyone quotes it, and the installation cost guide shows what the labor line should look like.
For the rest of the picture, the windows and doors guide pulls the family together.
