Sash, Exploded
Allow me, for a moment, to wax about about windows: They are the eyes to a building’s soul. The transom light above a Yankee barn door and the triple-hung sash in a meetinghouse facade help to distinguish a building, or relate it to its peers. Even when dismantling the most decrepit of barns, we are careful to preserve their idiosyncratic sash. Often, the sash has been adaptively reused, and may be older than the barn itself, reflecting the high embodied energy in these handcrafted elements. As craftspeople, one of the most important tasks we can undertake is the preservation of historic windows.
Some say that the preservation of old sash is at odds with energy efficiency, but this is a fallacy; it is only the neglect of old windows that make them unsustainable. A weatherstripped, double-hung sash in conjunction with storm windows will perform better over time than a vinyl window, and will be easier to maintain, and repair. In combination with the energy embodied in old windows, window preservation is not only the better aesthetic option, it’s also the greener one.
The ceiling, after cleaning
Late this Spring, one of our clients suffered a fire in the last stages of the restoration of their historic gymnasium. The building was originally was built for the Goodrich family in the 1910s; it has a monitor roof, and sides that are more window than wall. Last summer, we installed trusses in the monitor, and interior posts to support it. Unfortunately, a fire during the final painting phase left a car-sized hole in the floor, and the Titanium white paneling soot-black. Fire fighters saved the building by not only breaking every pane of glass, but most of the muntins too. We were called back in to repair the floor, the undercarriage and every one of the windows.
Gym Sash, 6-over-1 light
The first step was to carefully remove the sash, knotting the sash cord and leaving the sash weights waiting longingly in their pockets. The sash were transported to the shop and steamed in custom-built boxes to soften the glazing, and fifty years of paint.
After the paint was stripped, we popped the pins securing the mortise-and-tenons and dismantled the joinery. About half of the original stiles and rails could be restored, but the muntins (the molded bars that divide the glass) were smashed, sacrificed in the efforts to rescue the rest of the building, and the woods surrounding it.
Contemporary Muntin Profile
Window sash poses a unique challenge to a builder. The sash must be strong, to withstand the weight of the glass, and the forces applied by wind and by the folks who open and shut them. But windows must also be as lightly framed as possible, to allow the maximum amount of light through. In a many-lighted sash, the difference between the additional light let in by thinner muntins can be significant. In the Georgian period, when wooden dividers became popular, the molding profile was fat, round, and squat. The Georgian glazing bar was shorter, and the profile of the wedge of glazing was wider than it was high. Throughout the Federal and Revival periods, up to the Victorian, muntins lost weight, profiles became more delicate and oblong, and glazing bars were made narrower and higher. Over the same period, glaziers in the states transitioned from making crown glass, which was blown into 50″ rondels, and cylinder glass, in which glass was blown into 6′-8′ cylinders and cut open and laid flat, through table glass, in which the glass is poured onto a table and rolled flat, and, in the 20th century, to float glass, in which molten glass is floated over molten metal. The weight of the larger sheets of glass produced by these innovations only added to the challenge of creating strong and secure joinery.
Our first task was to locate materials. You’ll hear many a carpenter today complain that wood today just isn’t what it used to be. In taking apart old buildings, we find wood that has much tighter growth rings, with straight and even grain, than what you can find in today’s lumberyards. It is the paradox of old growth timber. Unfortunately for our forests, lumber produced from old growth is typically stronger and more stable. Fortunately, we were able to locate the old Southern Yellow Pine stock we needed from some boards we had saved for a special case such as this. Due to the requirements of the joinery, it is essential that the joiner uses tightly grained heartwood for window sash. For the glass, we cleaned and reused every scrap we could, cutting broken, larger panes into smaller ones. It was important to the client, and therefore to us, that the glass not be reproduction, and actually be as old as the sash. For the larger pieces, up to 26″ x 44″, we were calling all over the Northeast to find satisfactory glass.
Milling the muntin stock, fed from the left, and making good use of featherboards.
Reproducing the muntins was a multi-stepped process. We traced the muntin profiles and ordered shaper knives so that we could mill exact reproductions of the original stock. One shaper knife cuts the molding profile along the length of two sides of the muntin stock, as well as the interior face of the stiles and rails. Using fingerboards to hold the narrow (3/4″ x 1 1/4″) muntin stock against the fence, we ran one face of the stock through the shaper, then flipped it, and cut the opposite face.
In the 18th and early 19th century, joiners made muntins using a sash molding plane, that had a molded blade and body, and a sticking board, a custom jig that held the tiny stock for planing.
Coped Stub Tenon Joint
Okay Fit
Each end of the muntin is coped (scribed) to the profile of the stile, rail or muntin to which it joins. You may be able to find something similar in your kitchen, in the cope and stick assembly of contemporary cabinet doors: the ends of the rails of the door are coped and glued to the stile. The difference in window joinery (and in handcrafted cabinetry) is that the rails and cross muntins are also tenoned into mortises in the stiles and long muntins, respectively, and the long muntins are tenoned into the rails. A hollow-chisel mortiser streamlined the process of cutting 19 mortises for every 6-over-1 light window, while one 18-light sash had 24 mortises alone. A second shaper blade was used to cope the tenons on the rails and muntins.
Setting the height of the shaper blade, and coping the shoulders of the rails.
Traditional joiners would have used a coping saw, gouges and a handmade coping jig, that clamped to both sides of the muntin, and had the perfect negative of the molding cut into one end. A pair of precise shaper blades can make quick work of joining a completely new window today. However, the imperfections that give handcrafted work its character make coping new muntins to old stiles and rails a challenge. An airfoil shaped wood file came in handy to make the adjustments necessary for a snug fit.
Using the tenoning jig to cut a "dovepin" into a meeting rail.
Bridle Joint with a Half Dovetail
In addition to the coped mortise and tenons, the original window makers used a bridle joint with a half dovetail in the connection of stile to meeting rail. We cut the dovepins in the meeting rail by modifying our shop-made, tablesaw tenoning jig. This jig holds a rail (or any tenoned piece) vertically against the fence, in order to cut the cheeks of a tenon. In order to cut the pins, we ripped two long wedges at the angle of the dovetail, and used those to rotate the meeting rail, in order to adjust the angle at which it met the tablesaw blade. The jig was a handy solution to the complicated joinery, but we had to be careful to check and adjust the tablesaw with every cut, to account for variations in the old stiles and rails.
After the joinery was cut and fit, we assembled the sash and pinned the stile and rail joints. We prepared the glazing rabbets with primer and bedded the glass in a thin layer of putty. Pushing the glazier-points into the hard Yellow Pine was an oath-inducing experience. Then we kneaded the putty with linseed oil and whiting until it was warmed by our hands, and soft and pliable. We applied the glazing to the glazing bars like a child makes a mud pie, and then trimmed the excess with a even pressure and a steady hand. The glazed windows were then placed in a window rack for as long as we could let them set, before having to prime and reinstall them.
Sash assembled, old stile meets new rails. Note sash cord channel on outside of stile.
The ease of hanging the finished sash was a testament to old, double-hung window construction. In many old houses, the window weights can be accessed by a little door cut into the jambs, easing maintenance like changing a sash cord. The gym windows had no little door, and so we carefully removed the side casing in order to access the window weight pockets. We tied new sash cord to the window weights and knotted the other end of the sash cord that rides in the channel on the outside of the sash (see bridle joint diagram, above). Starting with the upper sash, we pressed the knot into the round hole at the base of the channel and then pushed that side of the sash against its track in the window frame (between the exterior casing and the parting bead.) The opposite stile was angled inside over the window sill. Then we pulled down the knot on the opposite jamb and pressed it into the cord channel on the opposite stile. With one parting bead removed, we eased the second side of the upper sash into its track, and replaced the second parting bead. The upper sash slid easily up and down in its track. We repeated with the bottom sash, replaced the window casing and any hardware, and moved onto the next window.
Six sash, repaired and installed.
Repairing hundred-year-old sash is a challenge, and a long process, but it is worth it. It preserves a building’s character, and improves it’s aesthetics. When combined with the proper weatherstripping, and appropriate interior storms, these windows can achieve the same U-values as modern double-paned sash. Most importantly, with the right maintenance, these windows will last another hundred years.
Click on the photos below for more information about our process:
