Why the wooden sash window is a brilliant invention:

 

Linseed glazing putty, which bridges glass and wood, is calcium carbonate based and meant to be sacrificial at this most vulnerable joint.  It fails after a few decades without compromising the wood sash.  This glazing joint is beveled and allows direct water run-off.  Modern wood windows remove the every-three-decade maintenance factor of linseed glazing by joining wood directly to glass, at the cost of rotting sash in 10-20 years.

 

Wood sash have vertical joint connections which are un-glued.  This directs water away from the sash with minimum impediment.  Being able to see hairline joint lines is a sign of health, rather than a water-infiltration point.  If the sash does need to expel moisture, it can do so at the non-visible sash perimeter (which slides along the jamb).  When the sash is sealed shut with caulking or paint, it loses this evaporation point and the rotting process is accelerated.

 

Traditional wood windows do not have a rigid track system as part of its functionality.  Because structures often shift over time, a track system would cause binding of sash once the window jamb gets out of square.  Many traditional windows use a rope and pulley for their functionality, a system which is not proprietary, easily understood, and easy to maintain.

 

The lines, proportions, and shadow aesthetics of a traditional window are not only beautiful, but give insight into intentional design elements which greatly slow down or block air infiltration, and at every point resolutely directing water away from the building.  The way in which the upper sash layers the lower sash, the double air block of the blind stop and parting bead, the way a wooden drip cap slips beneath wood siding above, the way the blind stop reaches far behind the brick curtain wall to safely deposit water to the weep holes, etc.  Modern window systems require complicated and doubtful weatherproofing measures and a building culture that is subsequently terrified of water leaks.  

 

Before Heating, Ventilation, and Air Conditioning technologies, a sash window worked with physics by dropping the upper sash five inches and raising the lower sash five inches - effectively circulating warm air out the top and bringing in fresh, cooler air at the bottom.

 

There's an inherent simplicity and transparency of sash windows that maximizes ease of repair.  Wood sash are designed to be deconstructed into perpetuity if necessary - to replace a sash part if needed.  This deconstruction doesn't void a warranty and doesn't destroy the sash in the process.