Historic Wood Windows

Contents

1. The parts of a sash window
2. The lumber in the frame
3. Why so many survived
4. The glass
5. Repair in practice
6. Weatherizing before replacing
7. The replacement argument
8. A trade in short supply

Mike Kobeissi’s work covers selling, remodeling, buying and building, with guidance on renovation and on staging and design, and in an early twentieth century house the windows are often the oldest working parts. A historic wood window, in the sense preservationists use, is an original sash window of solid lumber, most often the double hung type, in which two sashes slide past each other and are balanced by iron weights on ropes running over pulleys hidden in the wall, as the Los Angeles Times describes the mechanism.¹ Its origin, in the form most common in Southern California, lies in the building boom of the first half of the twentieth century, when dense old growth lumber was still the ordinary stock of construction.⁷

The parts of a sash window

This Old House lists the anatomy: casing trim covering the gap to the framing, glazing, side and head jambs surrounding the sashes, slender muntins dividing the glass, the sashes themselves, a lock joining top and bottom, and a sill angled to shed water.⁶ Casements, hinged at one side, also survive in older houses, though most repair shops concentrate on double hung units; spring balancers began replacing weights and ropes in the late 1920s.¹ The double hung form was also a cooling device: a century ago, the top sash was lowered to let warm air escape while the bottom one was raised to draw cooler air in, a pattern the owner of one restored Pasadena bungalow still uses.¹

The lumber in the frame

The material matters as much as the design. The National Trust for Historic Preservation notes that wood windows made before the 1940s are likely cut from old growth wood, which is stable and dense, mills cleanly, holds paint, resists rot and draws fewer insects.⁴ In Southern California, much of the lumber of that era was coast redwood. PBS SoCal’s Lost LA series traces how the region’s great building phase in the first half of the twentieth century coincided with the heaviest cutting on the redwood coast, and why clear, knot free old growth heartwood was superior to the second growth sold now.⁷

Figure

Traditional sash and a manufactured unit

	Traditional wood window	Vinyl or composite unit
How it is built	Individual parts: rails, stiles, muntins, stops, sill, jamb	Manufactured as a single unit
When a part fails	That piece is repaired or replaced in kind	The whole unit is replaced
Fit to the opening	Custom fit to the original opening	Stock sizes that often need the opening changed
Material	Before the 1940s, likely dense old growth wood	Synthetic frame and sealed glass

Why so many survived

Old windows lasted partly because houses were built differently. This Old House points to lead paint, now banned, which acted as a flexible coating that kept water out; to drafty rooms whose moving air dried moisture before rot could start; and to radiators under windows that kept sills dry.⁶ Tighter modern houses remove those accidental protections, which is why the same sash needs more attentive upkeep today. Reputation followed condition. The New York Times observed that old windows had spent decades branded drafty and inefficient, fixtures to be replaced rather than refurbished, before a growing number of owners began keeping them for appearance, history and cost.²

The glass

Original panes carry their own record. The ripples, lines and small bubbles in early glass came from the machine drawn cylinder process of the early twentieth century, and restorers in the Los Angeles Times piece said modern glass can be worked to imitate the ripples, though not the bubbles.¹ The New York Times quoted an Oregon restorer on the appeal of looking out through the same glass earlier occupants looked through.²

Repair in practice

The Los Angeles Times followed the repair of 17 original double hung windows in a 1907 Pasadena Craftsman bungalow, where only three had opened. The sashes came out, joints were tightened, cords replaced and weatherstripping added, and the owner reported a quieter, less drafty house. Restorers test the result with a “two finger test” of how easily a sash moves, and they sometimes plane sashes to fit frames skewed by settling.¹ The New York Times listed the routine that follows: keep paint fresh so water rolls off, check the glazing putty, leave jambs as bare wood except for weatherstripping, strip paint from sash ropes, and patch small areas of rot with epoxy.² The same report was candid about harder cases: lead paint often has to be removed completely, sashes painted or caulked shut by a previous owner can be difficult to free, rotted wood usually calls for a professional, and some windows are too far gone to save.²

Weatherizing before replacing

The National Park Service sets an order of operations. Caulking, weatherstripping and new glazing compound should always come before any thought of replacement, because heat escapes both through the glass and by air leaking around sash and frame.³ A storm window comes next. The Park Service cites a 2002 Lawrence Berkeley National Laboratory experiment finding that a storm window over a historic window can perform about as well thermally as a new low E vinyl replacement.³ Interior storms are preferred where exterior ones would hide decorative sash, and meeting rails should line up with the originals. The National Trust study found that weatherstripping an owner installs personally returned more than any other option it measured, and that the best retrofit depends on climate, since a house that mostly needs cooling gains little where windows are already shaded.⁴

Figure

Window inspection as the Park Service frames it

1. 01
   Routine maintenancePaint, glazing compound, caulking and weatherstripping.
2. 02
   Structural stabilizationLoose joints and weakened members made sound again.
3. 03
   Parts replacementNew pieces; when many are needed, a matching replacement may be weighed.

The replacement argument

The Park Service calls the belief that replacement saves as much as half of energy costs a misconception, says a replacement rarely pays for itself in a reasonable time, and notes that new assemblies cannot be repaired, only replaced again.³ The National Trust’s Saving Windows, Saving Money study reached a similar result: retrofits such as storm windows, cellular shades and interior panels performed comparably to replacements at a fraction of the cost.⁴ Restorers in the Los Angeles Times contrasted century old sash with vinyl units they said last about 15 years.¹ This Old House adds that vinyl softens at 165 degrees Fahrenheit and expands more than twice as much as wood with temperature, which can break seals over time.⁶ Standard sized units also tend to force changes to an original opening, distorting proportions.⁴ Repair is not always possible; the Park Service allows that when a large number of new parts are needed, a good matching replacement may be appropriate.³

A trade in short supply

The obstacle is often labor rather than wood. In 2011 the New York Times reported on the first National Window Preservation Summit, where restorers gathered in Kentucky to draft national standards for the work.² The Window Preservation Alliance, established in 2015, connects owners with restorers, and its president told the National Trust that the country has perhaps 500 of them, against about 3,000 if every county had one.⁵

Figure

A small trade

window restorers in the United States

about 500

restorers there would be with one in every county

about 3,000

year the alliance was established

2015

The evidence is strongest on energy and durability. Federal guidance, a national laboratory experiment and the National Trust’s own study agree that a maintained original window with a good storm performs close to a new unit and can be repaired part by part.³⁴ It is thinner on cost, where figures come from individual shops, and on how long particular replacements last. Those gaps make the Secretary of the Interior’s Standards, with their preference for repair, the usual tiebreaker on a National Register house, and the same reasoning carries up to the roof in the entry on clay tile roofs. The choice for any one house is best made with an inspector and a restorer who have seen its frames.