Everything You Need to Know About Windows: An Interview with Jay Eshelman of Woodstone
By Jay Eshelman
What should people be looking for in new windows for their home?
Of course, what people should be looking for depends, first and foremost, on what they want, considering the location and general character of their home or project.
But keep in mind, at Woodstone, we specialize in historic replications of all kinds. Not only do we fabricate windows and doors for homes, but for historic landmark buildings including schools, libraries, historic meeting houses, town halls, churches, hotels and country inns, to name a few.
If historic accuracy is what are clients are looking for, they should next consider cost, performance and serviceability. It’s one thing to fabricate an accurate landmark replication. It’s another thing entirely to fabricate an accurate landmark replication for a reasonable cost with today’s energy efficiency requirements.
For example, regarding cost, if your home or building was constructed 100 years ago, or 300 years ago for that matter, do you expect the building to last another 100 years or more? And, if so, how many times will the windows have to be replaced? Typically, Woodstone replicates windows that have already provided at least 100 years of useful service and you will be hard pressed to find a typical manufactured window fabricated today designed to last that long.
There’s a saying among landmark historic curators: if a window is ‘maintenance free’, it usually means the window can’t be maintained.
Most windows manufactured today are designed to be serviceable for the term of the average home mortgage, not 100 years or more. If something wears out or is broken, can the window be easily serviced or repaired? That’s the first thing our clients should consider. Does the building project warrant the investment in a window that will provide 100 years or more of useful service?
Can you explain some of the design choices people have when it comes to windows?
At Woodstone, a monumental (typically more than four feet wide and eight feet high) double hung window with Weight and Pulley balances, can have more than 500 specific elements making up a unit weighing 300 lbs. or more. Each of these elements include options for size, shape, thickness and finish. There are literally hundreds of different kinds of glass from which to choose, not to mention weather-strip and hardware functions, paint and stain finishes, and wood species. And still, performance specifications require that the 100 lbs. sash be operable with less than 30 lbs. of operating force while providing the required air infiltration performance. We once calculated that a several thousand page catalog would be required to list all of the options for one window type, which is why our web site shows design concepts, not specific products.
Architectural Forensics: In many of our replication projects, the detail complexity often includes replicating design and fabrication errors that occurred when there was a breakdown in the design control of the original project decades or even centuries earlier. Traditionally, for example, carpenters on a given building site fabricated the forms masons used to create openings for the windows. The on-site carpenters actually built the masonry forms, window jambs and trim on-site. Meanwhile, a local millwork shop fabricated and glazed the sash to fit in the site-built jambs. If, for example, the spring line, or center point, of a radius or elliptical curve in an arched top window was inadvertently misplaced on the horizontal layout grid, the arched top sash fabricated at the shop didn’t fit in the arched top masonry opening and jamb built on site without some shaving and tweaking.
One hundred years later, here comes Woodstone to replicate the old windows. But now we’re using high performance insulated glass and weather-tight hardware systems that require dimensional accuracy to the closest 1/64th of an inch, only to find there are gaps between the existing sash and jamb requiring some sort of compensation to make the unit appear and function to the required design and modern performance standards.
SDL v. TDL: One of the most significant window design considerations is choosing between Simulated Divided Lite (SDL) windows and True Divided Lite (TDL) windows. Mass-produced windows are often SDL and Landmark detailing is not typically a required or an important consideration with their use. But if landmark details are important and an SDL configuration is used, there are significant maintenance and repair issues to consider.
Remember the saying among landmark historic curators: if a window is ‘maintenance free’, it usually means the window can’t be maintained. SDL windows exemplify this issue. If a SDL sash is damaged, the glass breaks, or the IG seal fails, the entire sash must be replaced. On the other hand, if the IG in a True Divided Lite (TDL) sash is broken, or the IG seal fails, only the damaged pane of glass need be replaced. And if you’ve invested in an energy efficient monumental arched fanlight double hung window, fabricated in a superior high-resistance-to-decay wood species (e.g. Mahogany, White Oak, American Cherry, Teak or Walnut), with custom wood joinery profiles to match existing, and a custom stain matched asymmetric finish, and custom IG fabricated with restoration or antique glass, the cost to replace the entire sash can be a traumatic experience, if possible at all.
How does a window relate to the sound and temperature inside a home or room?
Sound: There are Sound Transmittance Coefficient (STC) tests for windows and doors and there are several details and elements we use to decrease the sound transmittance, which means registering a higher STC rating. Acoustics are an issue in many building types, airport terminals, for example, being an obvious application. Street noise in cities and privacy issues in rooms and apartments are common considerations. Depending on the location, a variety of airborne frequencies can be targeted.
In windows and doors, typically, the heavier or more dense the material, the higher the STC rating. Adding mass increases the rating. Using materials of differing density also blocks sound by creating offsetting frequency transference. For example, using 1/4″ laminated glass in an insulated glass unit in one leaf and 3/8″ laminated glass in the second leaf blocks sound because each piece of glass vibrates at differing frequencies thereby cancelling out the vibrations from each element to some extent. The air space between the two pieces of glass also blocks sound and how the glass is bedded in the sash has an effect too.
Temperature: We measure heat loss in most material elements and, like sound transmittance, various parts of a window or door can be tested. And again, as with sound blocking, the glass is the first element usually scrutinized and there are all sorts of glazing configurations considered.
For example, in very sensitive applications, the glass on the south side of a structure has different heat loss aspects than the windows on the north side of a structure. On southern exposures, glass designed to block heat transfer from the exterior to the interior is as important as preventing heat loss from the interior to the exterior. Wavelength sensitivity of the glazing element is also a consideration and we have computer models that diagnose the ultimate glazing specification for a given structure. That’s why we have Low Emissivity coatings, inert gas in the air space, single, double and triple air spaces and so on.
But most importantly, the feature usually forgotten in this consideration is the air infiltration performance of a given unit. We can use the most efficient materials available, but if someone leaves the window ajar on a cold night, all is for naught.
Even when we close the window tightly, the weather-strip systems are a crucial aspect of the heat loss performance features. Typically, the National Wood Window and Door Manufacturers Association, along with its Canadian equivalent, have established standards for air infiltration and Woodstone windows typically exceed those standards. In fact, Woodstone’s traditional weight & pulley double hung systems have been tested to exceed the NWWDMA standards by a factor of three. And keep in mind, these are the very same windows that have been known to be notoriously drafty in older buildings before energy conservation was the issue it is today.
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