In Defense of Old Windows II

This time a more subjective discussion of the value of old windows.

  • 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.

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David Amundson November 11, 2012 at 05:47 AM
I remember a structures class at U of I where the Prof. went on for a bit about how the allowable load limits for SPF dimensional lumber decreased across the decades as the timber being harvested got weaker and weaker. We could not replace this house on a 1:1 basis, no matter how much money we had to throw at the project.
Colin C. November 11, 2012 at 02:29 PM
Another great article, Mike. Thanks. Owning an older home can be an adventure. It helps to be somewhat handy and resourceful, but I wouldn't trade our 146 year old home in downtown Geneva for any development house or McMansion I've ever seen. My friends who own newer homes seem to run across as many problems, if not more than we do. Windows: homes built BAC (before air conditioning) usually had lots of large windows that could be opened for ventilation in the summer. One problem that we now face with these beautiful old windows is that they can be leaky and thermally inefficient. That's why a lot of people replace them and therein lies another error. The replacement units themselves may be perfectly airtight but the way they are installed may still allow lots of leaks around the edges. So, there is actually no gain in efficiency. What we have done, on two old homes is permanently seal the windows that we do not need to open. We painted the area between the window and old, wood sash storm, sealed all the cracks with caulk and painted again, put in the storm with wood screws, sealed all the cracks, then caulked the inside casements, including sealing any openings for counterweight ropes. Finally, we caulked around the outside of the entire window unit, inside and out. There has never been any leaking, condensation, or problem. Cost difference? DYI and it's a couple of bucks vs. a couple of hundred. And, it's easy to do.
Colin C. November 11, 2012 at 02:53 PM
And, speaking of thermal efficiency, another tip, if I may. People who know about this stuff will tell you that sealing all potential air leaks in a house is more important that insulation itself. That's why modern houses have vapor barriers, but usually they are installed with many leaks: cutouts for wall outlets, plumbing, etc. If you don't already have a powerful exhaust fan of some sort get a couple of box fans and put them in open windows to blow air out. Use cardboard and tape to close any gaps between fan and the side of the window. Close every other window, door, or any kind of opening in the house. Turn on the fans to create a slight suction in the house. Now light a bundle of 4 or 5 sticks of incense and, starting in the basement, go around every possible place that air might leak in: cracks between foundation and house, windows, plumbing and electrical openings, foundation cracks, everywhere. Hold the incense near the suspected crack and if the smoke wavers you have a leak. Seal it. BE CAREFUL!!! THE INCENSE CAN START A FIRE!!! Have someone standing by with an extinguisher. There are "smoke pencils" and other forms of non-burning smoke producers available. Go through the entire house checking and sealing every leak. In an old home, and probably even a new one, this one or two day project, which will cost a few dollars, can save hundreds of times that in reduced heating/cooling bills. It's well worth the effort.
Mike Bruno November 11, 2012 at 03:26 PM
Thanks for bringing up the weight pockets. Though I have not tried it, I have heard of one technique that has the weights running inside a PCV tube with the remainder of the pocket filled with insulation. It is probably very effective, but seemed like a repair nightmare should your sash rope break. A word of advice to any homeowner: If you ever have access to the entire weight pocket from the interior or exterior, don't miss the opportunity to seal any opportunities for air infiltration/leaks. Our home had been sandblasted in the 70s and I had to replace all the siding because it was falling off (most considered it a tear-down). I used the opportunity to put vapor barrier around the entire structure. (BTW: our replacement siding was custom vertical grain pine from a mill in Maine.)
Mike Bruno November 11, 2012 at 03:27 PM
I look forward to trying your technique some time.


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