How long do windows last

A window is a frame on one clock and a sealed glass unit on a faster one, and nearly every window decision goes wrong by reading the fast clock as if it were the slow one. The glass fogs at year 18, someone says “the windows are done,” and a frame with decades left gets priced for replacement.

What each part lasts

Part	Typical lifespan	What usually ends it
Timber frames	30–60 years	rot, paint failure, seal degradation
PVC frames	25–35 years	seal failure, hardware wear, colour drift
Aluminium frames	30–50 years	thermal-bridge failure, gasket degradation, coating failure
Double-glazed unit (IGU)	15–25 years	seal failure (fogging), gas loss, spacer degradation
Triple-glazed unit	20–30 years	seal failure, gas loss
Exterior timber door	30–60 years	rot, warping, hardware wear
Composite / steel door	25–40 years	seal failure, hardware wear, coating failure
Skylight / roof window	20–30 years	flashing failure, seal degradation, hardware wear

The ranges come from the durability handbooks and trade field data the planning model is built on. The pattern to take from the table: every frame material outlasts the glass unit inside it. A house glazed once will re-glaze its units at least once, often twice, before any frame is due, so “how long do windows last” is really two questions with two budgets.

Timber’s number has a condition attached

Timber frames reach 30 to 60 years only on a repaint cycle of about every 5 years. The paint is not cosmetic; it is the membrane that keeps water out of the joinery, and rot starts where the paint film fails, at the sill and the lower joints first. A timber window that missed two repaint cycles is aging on a steeper curve than its calendar age suggests. The same logic runs through exterior timber doors, on a refinish cycle of roughly every 4 years. PVC and aluminium trade that maintenance for a shorter, flatter life: nothing to repaint, less to extend.

The unit swap is the decision most owners never get offered

When a unit fogs, the honest repair is a new IGU in the old frame. The window seal replacement cost guide prices the two options: a replacement unit runs EUR 150–350 per window, a full window several times that. The gap is why the distinction earns its own decision. Run the annual-cost arithmetic honestly: a EUR 250 unit in a PVC frame at year 28 of 35 is buying years the frame may not have, while the same unit in a maintained timber frame at year 30 of 60 is the obvious call. You can check your own case in the free repair-or-replace calculator.

When to start planning

Sanna’s house in Turku was glazed in 2004: timber frames, repainted more or less on cycle, double-glazed units now 22 years old. Two units on the weather side have started fogging. The frames are at year 22 of a 30-to-60 range, mid-curve and sound; the units are at the end of theirs. She books a glazier for the failed units this summer and expects to rotate through the rest over the next few years as they fail, one by one, while the frames stay. New windows enter her plan somewhere in the 2030s, as a decision rather than a surprise.

What this means before you call anyone

Diagnose which clock ran out before asking for prices, because the trades sell what they are: a glazier replaces units, an installer replaces windows. A quote for full replacement when only units have failed is not dishonest, it is the answer to the question as asked. The plan in appkeep tracks frames and glass units as separate components, so the fogging year and the frame year each arrive as their own flagged decision instead of one alarming quote.