Sustainable Solutions for Old Windows

Plastic windows are often put into older buildings, to ‘upgrade’ wooden windows, though the pvc-U they are manufactured from gives them an expected lifespan of not much more than 30 years. They may provide improvement in insulation via double-glazing and improved draft-proofing and so are often viewed as the sustainable solution. This is potentially belied by the reduction in light transmission, pvc-U window’s limited lifespan and the carbon footprint created in their manufacture.  Pvc-U can now be recycled and one major manufacturer recycles up to 90% of old pvc-U windows, including the glass, though even this process has a carbon footprint in the energy used to re-create the window parts.

Listed historic buildings cannot be sympathetically re-fitted with modern plastic windows and the appearance of many otherwise handsome, though non-listed, older buildings has been spoilt by the addition of carelessly chosen replacement windows. The making, rebuilding and repairing of sliding sash windows has merit.

Wooden window frames and sashes of whatever age can be easily repaired if they have not been allowed to rot, though sliding sash windows in particular are often seen by the inexperienced as more trouble than they are worth to restore.  However weights, cords, pulleys and other traditional sliding sash accessories are readily available and slender, pre-manufactured double glazing units can sometimes be used to replace original Victorian glass, which was often especially thick in larger windows. An expertly restored wooden sliding sash should be no harder to open and close than a UPVC replacement.

Good timber is durable, if taken care of it will last for centuries, though it does require periodic maintenance involving paint and repair. Paint too has a carbon footprint, though modern non-volatile paints are improving all the time. Pvc-u is low-maintenance but cannot be repaired as easily, so its longevity is not as good and older plastic windows may suffer permanent discolouration from exposure to sunlight. They can also become stained, mildewed and bird droppings are reportedly particular problems.

Early steel windows, manufactured prior to the introduction of rustproofing treatments at the end of the 1930’s also require additional maintenance. Wartime painting was often neglected and rust allowed to set in, often unseen beneath the putty in the glazing rebates. Cracked glass, provoked by compression from the building up of corrosion products, is a sure sign.

Such windows are often worth conserving and may be put back in good order. Careful removal of glass and putty, followed by grinding off rust to bright metal and the application of a good zinc based primer is essential, before re-glazing and painting.

When extensive conservation work is required, involving the repair or replacement of hardware, the dismantling of composite assemblies, or the piecing in of replacement bars, it may be worth having the windows taken out, removed to a workshop, stripped down and hot dip galvanized before re-assembly.