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Old-House Online » Old-House Tips, Restoration Stories, & More » Repairs & How To » Restoration Projects » How To Weatherize Your Windows

How To Weatherize Your Windows

Learn how to keep warm throughout the winter with thermal tune-ups for your windows. Story and photos by Steve Jordan

    Decades of sloppy paint buildup on working surfaces leads to leaky sash and drafts. Simply removing bumps, drips, and excess (especially along the meeting rails at the midpoint of the window) and adjusting stops will improve the seals.

    Decades of sloppy paint buildup on working surfaces leads to leaky sash and drafts. Simply removing bumps, drips, and excess (especially along the meeting rails at the midpoint of the window) and adjusting stops will improve the seals.

    Does the return of cold weather tempt you to consider high-powered ads for new windows that promise to lower your energy bills and add value to your home—all for “one-time-special” offers?

    Well, think again. Your old, sticky, low-tech windows are probably more cost-effective than they seem. They simply need a little tender loving care to provide efficient, trouble-free service for another half century or so. Cleaning off old paint drips and tightening up the stops works miracles, but adding efficient, top-of-the-line weather strips can make your windows competitive with the best of replacement systems and helps with sash window repair.

    Look for Problems

    First, take time to assess the working condition of your windows. Before examining the window itself, look for drafts with the time-honored smoke test—that is, on a windy day, pass a smoke source (a cigarette, incense stick, or candle) around the frame and see if you can pinpoint any conspicuous air leaks. Next, operate your lower sashes. Do they neatly glide up and down, or do they stick or wobble from side-to-side? Ideally, the sashes should travel easily but snugly in their channels. If not, investigate why. The biggest impediment to fluid movement is usually sloppy accumulations of paint at the sash stops, sash stiles and rails, and sash channels.

    To clean off this paint, remove the stops and sash and place them on sawhorses or a stable work table. On the faces of the stops that contact the sash, remove thick paint with a paint scraper or sander, clamping the stops to your work platform to keep them steady. Next, remove heavy or bumpy accumulations of paint on the sash rails and stiles with a sander or, if exceptionally heavy, a heat tool. Also check the edge of the stool that drops to the sill. Before reinstalling the sash, scrape off any paint accumulation along the parting stops (also called beads) and sand them smooth. While you work, observe proper lead paint safety precautions (see “Looking Out for Lead,” November/ December 2002). I find that rubbing a little floor wax along these working surfaces also helps the sash move smoothly.

    Ideally, the sash stop moldings just inside the window should be constructed with screws or slotted hardware that permits adjusting for a snug sash in winter.

    Ideally, the sash stop moldings just inside the window should be constructed with screws or slotted hardware that permits adjusting for a snug sash in winter. (Illustration: Rob Leanna)

    Adjust Sash Stops

    Sash stops—the two vertical moldings just inside the window—serve two functions: They hold the sash in place, but they also adjust to secure the sash against wind infiltration. When sash stops are attached with nails, they cannot be adjusted, so their initial placement must be a careful balance—not too tight and not too loose. Normally, the sash side of the stop is flush with the stool edge; this way the stop guides the sash smoothly to the sill. In most cases, the upper edge of the stop joins the head stop, and here it’s acceptable to have a loose fit, because when the sash is up drafts are not an issue. Properly adjusting the bottom range of the stops, however, is most important for smooth operation and thermal efficiency.

    The most versatile method for adjusting stops uses screws and washers or stop adjuster hardware made for this purpose. When installed correctly, they allow the stops to be loosened for “throwing up” the sash in warm weather, and tightened to seal out drafts in cold weather. Stop adjusters are brass or chrome washers that fit holes bored in your stops, usually five in the average-height window or three in a short kitchen or bath window. The adjuster hole that accepts the screw is actually a slot that allows the stop to be moved in and out. Stop adjusters typically use 1 1/4″ # 8 brass oval head screws—slotted for historic applications or flat-head Phillips for other windows.

    If you don’t have actual stop adjusters, wood screws and finishing or cup washers will accomplish the same result. Bore oversized holes (larger than the diameter of your screws) in the stops that the washer will cover. Then screw the stops on and adjust them as desired. For symmetry, position every screw at the same height as its mate on the opposing stop in every window throughout the room. Do not caulk the sash stops to the frame; it renders the adjusters useless.

    A final recommendation for tightening up loose windows without major surgery is to install cam locks (Ives Side Window Locks are one brand). Sometimes called banjo fasteners, these are small, lever-actuated brakes that, when mounted on each stop, push the sash into the parting bead as tightly as possible.

    In a basic installation, bronze V weatherstrip is nailed across the bottom and up the channels where the lower sash rides. The flexible flange of the strip faces the exterior and is cut at an angle where it meets the sill. Note there are no nails over the weight pocket door.

    In a basic installation, bronze V weatherstrip is nailed across the bottom and up the channels where the lower sash rides. The flexible flange of the strip faces the exterior and is cut at an angle where it meets the sill. Note there are no nails over the weight pocket door.

    Weatherstrip Lower Sash

    When upgrading historic windows in cold climates, combining weatherstrips with the above mentioned tune-ups creates the most energy efficient installation. Although there are many methods and materials used to weatherstrip windows, I generally choose durable metal weatherstrips. When pliable weather strips are called for, I use only EPDM rubber because it lasts longer than inexpensive vinyl alternatives and is not vulnerable to temperature changes.

    Bronze V -Type Weatherstrip. For most applications, bronze V-type weatherstrip (about $1 per linear foot) is a perfect, inexpensive solution. To install the sash channel strips, take a pair of tin snips and cut two pieces slightly longer than the distance from the sill to the top of the meeting rails. Note that the apex of the V should face the interior of the house. Next, cut the sill end at a slight angle that conforms to the 12- to 15-degree slope of the sill, cutting from the strip apex down. On the opposite end, cut the strips even with or slightly below the top of the meeting rail. Round off the sharp edges at the top of the weatherstrips to prevent them from snagging on the sash. Then taper the angle back on the loose side of the sill end.

    Cut the side strips from the fold outward to match the sill angle

    Cut the side strips from the fold outward to match the sill angle.

    To attach the strips, you need only a few brads. These usually come with the weatherstrip, and should be brass or copper (or at least brass- or copper-plated) to prevent galvanic corrosion between dissimilar metals. Place one strip against the parting bead and, holding a brad with needlenose pliers, secure it at the bottom near the sill using a brad or tack hammer. Moving upward, next install one or two brads up to the bottom of your sash-weight access pocket. Do not nail brads into the weight-pocket door because it will bounce. (If you do, you will surely bend two dozen brads, lose more, ruin the weatherstrip with your hammer, and bruise your fingers!) Instead, move above the access panel and install a few more brads, ending about 1/8″ to 1/4″ from the top of the strip. Six or eight brads over the entire length of weatherstrip is usually plenty.

    Cutting the side strips

    Secure the strips with needle-nose pliers and a light happer. The fasteners should be copper (or copper-plated) brads to avoid galvanic corrosion that would eat through the thin strip of metal in a few seasons.

    You can install the sill strip either on the sill or on the bottom of the sash. If you choose the sill, angle-cut the flexible, flange part of the metal on the ends to prevent it from snagging on the channel strips. Bronze V weatherstrips can also be installed on meeting rails (especially if they are made for this purpose), but with basic types snagging is frequently a problem. Alternatively, clean meeting rails pulled tightly together with sash locks should make a sufficient seal. For exceptionally wide sash—say, 36″ or wider—I like to use two sash locks. If the weatherstrips make the window too tight or too tall at the meeting rail, plane the sash stiles or bottom rail slightly until the sash moves and seats appropriately.

    Flanged Weatherstrip. The old-fashioned flanged weatherstrip that forms an integral seal with the sash might just be the best ever invented. It was used on better quality homes from about 1900 until 1950, and is commonly found in perfect working condition after a half century or longer of service. Although made in both zinc and bronze, the bronze version is substantially more expensive and probably more prone to damage if removed and reinstalled.

    You order flanged weatherstrip from the manufacturer cut-to-size; therefore, all measurements should be precise and at hand when making the order. Expect to pay about $2 to $3 per linear foot for the zinc materials, including brads. It is sold in 1 3/8″ widths (the typical sash thickness) and in 1 3/4″ widths.

     The raised “track” on a flanged weatherstrip slides in a groove on the sash edge, creating an integral seal. Locate the proper position for the groove by laying the strip upside-down on the sash.

    The raised “track” on a flanged weatherstrip slides in a groove on the sash edge, creating an integral seal. Locate the proper position for the groove by laying the strip upside-down on the sash.

    Your first step in installing flanged weatherstrips requires a router to cut a groove into three sides (two stiles and the bottom rail) of your sash to accept the weatherstrip flange. On the lower sash, the flange groove is located near the exterior edge of the sash. By placing the strip backwards on the sash, locate the center of where the groove should be cut and mark it. Next, using an 1/8″ slot cutter bit, adjust your router and bit to cut the groove evenly along the three sides of the sash. (Some people also make this groove with a table saw, but I do not recommend it.) After you have routed the sash, insert your strip to make sure the groove is wide enough to allow the flange to move up and down. There should be a little friction, but not enough to restrict movement of the window.

    Cut the flange with a router and 1/8” bit, or whatever size produces a good fit.

    Cut the flange with a router and 1/8” bit, or whatever size produces a good fit.

    Begin your installation with the sill strip, which should fit as it comes from the package. To prepare the channel strips for installation, cut the top flange off at a downward angle to prevent snagging on the sash channel or sash cord. (Like bronze V strips, the flanged channel strips extend past the top of the meeting rail.) Then cut the bottom to conform to the angle of the sill, and to fit around the stool (the indoor sill). Note that the flange should be angle-cut high enough to saddle the bottom weatherstrip. Facing the window, install the left-hand piece of stripping using only three to five brads—one near the sill, one about midway up and one near the top. Again, avoid nailing into the sash-weight door. Next temporarily insert the sash, making sure the groove and flange mesh at the left and the sill. Then check to see that the window moves up down appropriately.

    If you have existing flange weatherstrips, you can often replace damaged sections with new.  When you angle the bottoms of side flange weatherstrips to match the sill slope, you must also adapt the flange so it straddles the flange of the bottom strip, and probably trim where it meets the stool.

    If you have existing flange weatherstrips, you can often replace damaged sections with new. When you angle the bottoms of side flange weatherstrips to match the sill slope, you must also adapt the flange so it straddles the flange of the bottom strip, and probably trim where it meets the stool.

    Remove the sash and prepare the right-hand weatherstrip in the same way. Insert the sash cord into the knot hole in the stile and install the left side of the sash into the left-side weatherstrip. Then insert sash cord in the right side, and weatherstrip into the groove of the right sash. Using a thin blade putty knife, gently push the sash and strip into the sash channel. Once the sash is seated, pull or push the right-hand weatherstrip down until it saddles over the sill strip. It is important to thoughtfully locate the brads on this piece so that you can remove the sash in the future by reversing the process. Insert the bottom brad near the sill. Insert the upper brad at the inside edge of the sash and weatherstrip edge so that it can be removed if necessary. Before installing the stops, make sure the windows glide up and down.

    Install Storm Windows

    Energy studies conducted by the federal government and many universities indicate that the combination of an adjusted prime sash and good storm sash is as efficient as most replacement windows. The best storms—thermally and aesthetically —are wood-framed but, alas, these have worn out their welcome with all but a few die-hard preservationists. Many sash and lumber companies still make wood storms and, when consulted, I recommend mahogany, Spanish cedar, or western red cedar for the frames. These are usually made from 5/4 lumber (actually about 1″ thick) and double-strength glass. Wood storms should not fit too tightly into the window frame, but they should be screwed or fastened snugly.

    Storm windows should not form an airtight seal but, instead, incorporate weep holes or be raised on lead shims to let moisture escape.

    Storm windows should not form an airtight seal but, instead, incorporate weep holes or be raised on lead shims to let moisture escape. (Illustration: Rob Leanna)

    Aluminum Storms. Triple-track storm sash made of aluminum is typically used on most older houses where the original windows are intact. Triple tracks allow the lower storm panels and screens to be reversed with the changing seasons, minimizing the biyearly switcheroo chore, but this savings in time and energy has its cost. Aluminum is an excellent thermal conductor so it is not much of a barrier to heat loss. The real job of triple-track storms, then, is to prevent wind infiltration, and when installed properly they do this adequately. Some older storm sash—say, from 20 to 40 years ago—did not have integral weatherstrips but relied on cams to tighten the windows in the frames. These usually still work fine after many years. However, older storms that were manufactured with thin-pile weatherstrips often need to have the pile replaced. Many hardware stores or glass companies specialize in this work. In general, it is economical to replace the screen or a glass in a storm sash, but if both screen and glass are shot, it is more economical to purchase a new storm sash.

    The problem behind the poor operation of many aluminum storms is that they were installed carelessly. On their own the aluminum frames are flimsy so it is important to install them with both sides plumb. If the frames spread at the center, the screen or storm latches that slide in the frames will fall out of their channels, making them useless. If the frame is racked, the panels will jam.

    Many installers set the frame in a bead of caulking for a good seal. This is acceptable, but I like to omit this bead and instead apply a thin bead of caulking after installation. This makes it easier to remove the frames for painting and glazing windows and makes for a better job in the end. Finally, never fill the two or three small weep holes at the sill level of the storm. These holes allow condensation to dissipate during the winter, and rain to drain if it enters the screen panels in summer.

    Interior Storms. Storm windows can also be used on the inside of the prime sash. Interior storms are popular when exterior storm sash obscure unusually attractive windows, and in impractical situations like extremely high windows or swinging-out casements. Interior storms are usually made with a large piece of Plexiglas in a frame that attaches to the prime sash frame with magnets, Velcro, or screws. In some applications, the interior frames must be altered to accept the interior storm sash. There can be tradeoffs to interior storms, however: first, there is no exterior protection of the prime sash; second, the sash is cumbersome to open if ventilation is needed; third, condensation trapped between the storm panel and the prime sash can deteriorate the prime sash. Still, interior storms can be a blessing when exterior storms are not feasible. Many companies specialize in interior storms and some hardware stores and glass companies also make them to order.

    Published in: Old-House Journal November/December 2004

    { 1 comment… read it below or add one }

    Catherine Brooks, Eco-Strip July 20, 2012 at 10:10 am

    Great detail on removing sash, restoring and weatherizing old, hardwood windows. But that first photo and the description of the author to dry scrape and open sand the old paint is frightening. Pre-1978 houses usually have lead-based paint. Any disturbance of this paint needs great caution to protect the worker and occupants. All that paint dust should be carefully contained and disposed of daily. It only takes a tiny amount of this dust to poison developing children and cause irreversible brain and nervous system damage. See http://www.epa.gov/lead. Wet scraping with water misted on surfaces, dry scraping or sanding ONLY with a HEPA vacuum attachments, or scraping heated and soft paint into clumps will contain the dust well. Low infrared Speedheater heats paint to only 400℉ and does not release lead fumes like heat guns, heat plates and torches.

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