How long does a leaded glass window actually last?

The windows I restore most are 80 to 130 years old. The glass in them is original. The lead has been replaced once, maybe twice. The putty has been refreshed a few times. But the window itself, its design, its presence in the home, has been continuous for over a century. That's what a well-built leaded glass window actually is.

What actually wears out

The glass doesn't. Properly made lead came lasts roughly 60 to 100 years before it gets brittle enough to need replacing. The linseed oil putty that seals and stiffens the panel dries out over a similar timeframe. Both are completely serviceable when either reaches the end of its life, the window gets re-leaded and re-puttied. Then it's good for another hundred years.

What shortens the lifespan

Neglect, mostly. A broken piece that isn't fixed lets moisture in and accelerates everything around it. A window that starts bowing and isn't stabilised eventually separates from its frame. The problems I see in very deteriorated windows almost always come from small issues that were left alone for too long.

Exposed positions age faster too. A south-facing front door window takes more weather than a sheltered interior transom. For windows in particularly harsh positions, encapsulation is worth thinking about because it takes the original glass out of direct contact with the elements entirely.

What this means if you're commissioning something new

When I build a window, I'm building it with this timeframe in mind. The lead I use, the putty, the way I construct the panel, it's all done with the assumption that this window should still be in this home in a hundred years. That's a big part of why I care about doing it right. It's not decoration, it's something that lasts.