Window jargon buster

You don’t need to memorise any of this — just knowing where to check is enough. Keep this page open while you read a quote, or before your home survey, and the conversation will feel a lot less like code.

Energy and glass

• U-value — how much heat a window lets escape. Lower is better; a modern double-glazed unit is typically around 1.2–1.4 W/m²K.
• Window Energy Rating (WER) — a whole-window efficiency band from A++ down to E, similar to the labels on fridges.
• Low-E glass — glass with an invisible coating that reflects heat back into the room.
• Argon-filled — an inert gas sealed between the panes to slow heat loss.
• Spacer bar — the strip separating the panes; “warm-edge” versions reduce cold spots and condensation.

Frames and opening styles

• Casement — the common style hinged at the side or top.
• Sash — traditional windows that slide vertically, typical of period homes.
• Tilt-and-turn — opens inward two ways, for ventilation and easy cleaning.
• uPVC / timber / aluminium — the three main frame materials, differing in cost, look and maintenance.
• Trickle vent — a small controllable slot that lets fresh air in without opening the window, often required under Building Regulations.

Quotes, standards and guarantees

• FENSA / CERTASS — competent-person schemes that let an installer self-certify their fitting to Building Regulations.
• TrustMark — a government-endorsed quality standard for tradespeople.
• Insurance-backed guarantee (IBG) — cover that protects your guarantee if the installer stops trading.
• Deposit protection — a scheme safeguarding any deposit you pay before work begins.
• Making good — the plastering and finishing around new frames once they’re fitted.

With the language decoded, reading a real quote is much simpler — head to understanding a window quote line by line, or step back to the full quote process for the big picture.