In Defense of Old Windows II

• Author's Note: In the interest of full disclosure, I (Mike Bruno) sit on the Historic Preservation Commission for Geneva, IL. The opinions here are my own and do not necessarily reflect the opinions of the commission or the city of Geneva.

It has been some time since I last discussed windows. Events got in the way of my following up my previous post on windows. In that post I made case that the economics of replacing your vintage windows was usually a bad economic decision and, at best, a dubious ‘green’ decision.  In this post, I wish to make the case for the intrinsic, subjective value of your old windows.

Let’s begin with the materials.  If your windows are of a certain age (mine are 105 years old), the lumber comes from “old growth” forests.  That is to say, a lumber company went out into, what might well have been, an ancient pristine forest that felled a tree that had been quietly competing for its share of sunlight for some centuries alongside its neighbors doing precisely the same thing. This flora may have struggled into existence when the British colonies were just fledgling encampments before some gristly men laid their saw to its trunk.

It took many years, but we (as a society) eventually came to realize that the decimation of vast tracts of ancient virgin forest might not be a terribly good idea. Today, most lumber is taken from managed forests that are harvested and replanted by the landowners. This is a good thing. Proper management of a forest can yield more lumber while preserving threatened natural lands for future generations.

What this means is that your older windows were likely made from “old-growth” lumber instead of managed “fast-growth” lumber…and it is not comparing apples to apples. Were one to look at a cross section of a piece of old-growth lumber, you would see the annual growth rings very tightly packed. Sometimes these rings are so close you need a magnifying glass (or better) to even distinguish them.  It is these rings that are the structural and decay resistant component of lumber.  The material separating the rings is a far softer and porous material that the tree laid on during its growing season. Fast-growth lumber can often have growth rings separated by 1/8” or more! This makes new growth lumber primarily composed of the soft porous material and relatively little of the structural “ring” material.  Let’s call the dark portion of the rings “rings” and the light, soft portion “pulp” for our discussion.

[A little digression here: for you physics geeks out there, I know … it’s all “structural/"  I am just focusing on the relative structural value of the rings and what lay between them.  No flames please.]

What all this means is that any new wood window, even the most expensive, is almost certainly made from fast-growth lumber. Old-growth lumber is, for all intents and purposes, extinct as far as building materials go and you won’t find any at Home Depot. Because of the tightly packed rings of old-growth lumber, that lumber has dramatically higher strength and much better water and decay resistance. The structural characteristics are different enough that building codes had to be rewritten to account for the lower strength of fast-growth lumber as when it began to dominate the market.

This translates into window design, construction and longevity.  Right away we should recognize that there are century-old windows that are still serviceable.  Don’t even think about buying a new window that your great-great-grandchildren will be able to use. The superior strength of old-growth wood allows the most slender muntins (the wooden component separating pieces of glass).  It is not physically possible to make a muntin as slender as some older windows despite resellers saying “It will be ‘identical’ to your old window.”  Given that windows (often called ‘the eyes of the house’) are such an important architectural component, even these subtle dimensional changes can appreciably alter the appearance of the building…particularly when viewed at an angle.

Consider too that the windows in an old home are also the most artisanal of the visible features. The finest materials were reserved for window millwork and are more pieces of furniture than construction materials. The most skilled craftsmen were used to mill and assemble your old windows.

Even the glass is an important feature of your older windows. Today’s glass is formed by pouring molten glass on top of a pool of molten tin. The glass would float on top of the tin and gravity spreads it out perfectly flat. This is called ‘float glass’ and became the norm back in the late 1950s. Before then, the norm was ‘cylinder glass’.  A glass maker would blow a large glass bottle in the shape of a cylinder.  Once the cylinder was large enough, it was cooled, the ends removed and cut lengthwise, reheated and laid flat on a prepared surface. The variabilities of temperature, impurities and handling would impart some imperfections and a characteristic waviness that you might be familiar with.  

It’s pretty obvious the advantages of float glass over cylinder glass. Looking through float glass, you may be unconscious even of its presence. Wavy cylinder glass, on the other hand, can become part of your viewing experience and you are often conscious of its presence. Speaking for myself; when I gaze out my wavy front windows to the streetscape, I am reminded of the generations of families that have gazed out at the same. It feels as those wavy windows have captured a part of the spirit of my predecessors. This is true, too, for passersby outside the house. The wavy glass makes it presence known in the reflection of that same streetscape. New windows, by comparison, seem to mutely and dispassionately avoid interaction with the viewer.

We have already touched on the very real merits of old-growth lumber, but what about the merits of contemporary materials? Vinyl and aluminum are rot-proof, right? Indeed they are, but if your motivation is long-term money savings, there are other issues to consider that I have talked about before. Consider that vinyl has a very high “thermal expansion coefficient”. This means that a solid vinyl window can swell and shrink measurably with the change of seasons opening up gaps and contributing to air infiltration and short life-spans. (Statistically, replacement windows last a mere 16 years). Moreover the vinyl and aluminum-clad windows are typically NOT designed to be painted and will often have a glossy exterior finish...a finish previously unknown in residential architecture.

Almost invariably, replacement window resellers will say “These will look just like your old windows.” Seldom is this true. Consider the muntin pattern. The muntins on an older windows are the slender wooden components that divide the individual small panes of glass. These are know as “true divided lights”. The most affordable replacements (the ones that are priced low enough to make you consider window replacements) will try to simulate these muntins by applying a grill to the interior or exterior. These can be passable from a great distance, but consider that we could probably replace the Mona Lisa with a facsimile that looks passable from a great distance. Even a casual inspection of these low-priced replacements reveals them to be poor imposters.

The most expensive simulation of true divided lights is a grill applied to the interior and exterior along with a spacer between the two insulating panes. This option is available in the most expensive replacement windows which often cost magnitudes more than a basic restoration of an historic window.

If we value our history and wish our community to reflect its past, then maintaining the historic windows is one of the most important aspects managing that history. We could have a faux Mona Lisa that might not require the climate control that care that the real Mona Lisa does, but we are richer for having Leonardo da Vinci’s original instead of a polyvinyl copy. Given the dubious value of replacing them, we are all richer by having our old windows.