It’s bad to clad!

Property owners occasionally ask whether historic wood windows and trim can be clad in sheet metal to both eliminate maintenance and protect fragile historic material. As conservation advisers, we discourage cladding since it removes, in effect, a character-defining element from the building, and cladding raises maintenance issues of its own.

Tempting though it may be, simply covering up deteriorated areas can ignore the causes of deterioration, leaving underlying moisture or other problems to continue their destructive work within the structure.

Wood sills, as an example, may be weathered rather than actually rotted and can often be treated relatively easily and economically with wood epoxy repairs. Once repaired, the repainted wood is stable, rot-resistant and easily maintained.

Sheet metal cladding, on the other hand, takes skill to properly detail, fit, and install so that it drains properly. Once installed, claddings often rely on caulking to seal open edges. Caulking can attract dirt and, like the painted surfaces it conceals, needs to be maintained and periodically replaced. Perhaps most important, clad wood is no longer exposed to the drying effects of the sun and circulating air, so that if water does gets beneath the cladding, as it likely eventually will, deterioration can occur rapidly and unnoticed. Better the devil you know…

This isn’t to say cladding is always inappropriate: it may be a valid means of adding a weather detail missing in the historic element while minimizing impacts on heritage value. In general, though, it’s preferable to have an authentic original material that you can appreciate and easily maintain.

Written by: Fraser Shaw, Heritage Conservation Adviser.

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