How to Install a Storm Window

water dew on storm window

Storm windows may be the solution you are searching for to add comfort in your home without replacing existing windows, as they are less costly and can reduce drafts while saving energy costs.

Before ordering a new storm window, take measurements of each window casing opening and determine its type (Western or Eastern casing), which will affect how the new storm fits.

Tasks checklist to install a storm window

Measure the Window

In order to achieve proper storm window fitting, they must correspond with the size of their window opening. This step applies both interior and exterior models that mount either on top of casings or between casings, or reveal models.

Assuming your frame measures 10″ on both sides, take measurements at three points along its height – left, center and right – then select the lowest measurement as your window height.

Make sure that the frame is square by using a framing square to test its edges, taking measurements at its corners if it appears bowed and taking note of its meeting rail location and whether or not it lines up with main window hardware. Finally, examine the window sill for weep holes and adjust expanding bottom rail to touch weep holes – this prevents moisture leaking between main and storm windows [source: Baker]. For double-hung storm windows make sure their meeting rails line up with main window hardware [source: Baker]. If possible ensure meeting rails line up properly between double hung storm windows [source: Baker].

Measure the Frame

If you plan to install storm windows into an existing frame, begin by measuring both its dimensions and thickness using a framing square. Take measurements both top-and-bottom to account for possible imperfections in your home that could affect how you measure.

how to install storm window frame

Note: When reporting dimensions for storm windows, their final dimensions depend on whether you intend to mount them using an Eastern or Western-style casing. An Eastern style mounts the storm windows so they hang inside of the window frame so they can slide up or down like your existing window does.

Western-style casing requires storm windows to hang outside the window frame, where they must be slightly larger so they can open and close freely with minimal resistance from their slim casing. Any differences are minute, making adjustment simple.

Measure the Casing

New storm windows may be costly upfront, but over time they provide significant energy savings and don’t need to be removed for routine maintenance – unlike replacing primary windows with new ones.

Existing storm windows can save money when installed on a track instead of directly attached to their casing, providing another method for cost savings. To do this, measure the height of the casing before proceeding.

Place the end of your tape measure into the TRACK you found earlier (where the screen will slide up into). Locate LIP at the base of casing directly below TRACK as this is where storm window will slip behind and keep it secure.

Measure the width of the opening in three places at the bottom, middle, and top of the window casing (rounding to within 1/8 inch for accuracy). Select the smallest measurement when ordering a new storm window.

Measure the Glass

Interior storm windows are placed within existing window stops to seal them tightly, eliminating drafts and condensation. To measure for interior windows, take measurements on either side of their casing before writing down the smallest dimension (as detailed here) to order your storm window. Alternatively, for Western style storm windows measure from jamb to jamb rather than its edge when measuring window opening width.

install storm window glass

Exterior storm windows require similar measurements when taking measurements for their window openings, although height measurements should include either a drop sill or standard sill as part of their measurements. Therefore, when taking measurements it’s advisable to measure three points: bottom, middle and top of window if applicable if height measurements differ; use the smaller dimension when ordering storm window replacements if applicable if using double-hung or sliding storms with tracks during measurements.

Measure the Sash

Storm windows are custom-fit, weatherproof inserts designed to cover primary windows. Their primary function is limiting air infiltration while simultaneously providing energy savings and protection from storm damage to their original window occupant. To maximize these benefits, it’s essential that each storm window fits snugly. Taking time and care in fitting it securely can increase its benefits exponentially.

To size the new window, begin by measuring its opening from inside jamb on both left and right sides, recording the narrowest measurement which will become your casing opening width. If your house features Western casing, storm windows should be 1/4 inch smaller than casing opening; otherwise they should be up to 1 and 1/4 inches larger [source: Baker].

Close the window, then measure its height from outside the frame at its bottom sill – this will become the height of your new window and can help you purchase one in its appropriate size.

Cut the Glass

Storm windows must seal tightly against both window frame and sill for optimal performance, preventing heat or cold from escaping and air from coming in through any openings or gaps in their seal. Prior to beginning installation of the storm window, make sure any existing window is in good condition, any necessary repairs have been completed (for more on that topic please read our article about window repair) and all required steps have been taken (please refer to our article on window repair for assistance).

Interior storm windows require butyl caulk to seal their edges, with drainage holes left uncaulked for drainage purposes. When positioning their new storm window in their existing window opening to inspect fit and see where movable panels (if applicable) operate from. Once satisfied with their fitment and centering in their openings.

Cutting Glass to install storm window

Use a tape measure to take three measurements along the bottom and middle of your casing to check that its vertical measurements are equal; if they are, then your window is square, and you can start screwing it into its place.

Cut the Casing

Storm windows can boost energy efficiency, decrease noise levels and dust accumulation, and prevent moisture intrusion through primary window frames. To be effective, however, the storm windows must fit securely to existing window frames and seal appropriately to stay sealed against moisture entry.

Tom Silva of This Old House general contractor suggests that quality storm windows should be specially ordered to fit within either the window trim or stop, depending on if they’re an overlap or interior mount type. To prevent condensation between existing window and storm window, caulking around top and sides of frame before trimming is advised in order to minimize condensation issues.

Place the new storm window into its opening to make sure it fits securely and comfortably. Determine which side is at the top by noting the direction in which movable panels (if applicable) operate, and if needed shim the bottom expander up so as to contact with sub sill. If needed if too tall simply shim it back until bottom expander contacts sub sill

Install the Casing

Storm windows can be an invaluable addition to your home, whether you live near a busy road or simply wish to reduce noise from neighboring properties. Storm windows provide much-needed temperature regulation and draft protection as well as protecting primary windows against damage or burglary.

If selecting an interior storm window, take three measurements at the bottom, top and center of the window – as these windows may not always be square – then order the one with the smallest measurements.

curtain for installed storm window

An Eastern-style casing typically requires a storm window that measures 1 1/4 inches wider and 1/2 inch taller than its opening’s smallest measurements, to fit over the blind stop inside the casing. For an attractive result, paint the new storm window frames the same color as exterior trim and sash; before installation apply butyl caulk along only its top and side edges – do not apply butyl caulk around its rear edges!

Install the Sash

Storm window installations must provide an airtight seal to reduce air infiltration and increase home energy efficiency. Installing the sash and frame yourself saves money, time, and can be less stressful than working with an upper casing system.

Use a tape measure to assess whether your new window fits as planned, making sure it is square with its hole (not lopsided). Before fastening any screws, place the glass into its proper place. For triple track-style windows, test their operable panels to see if they close and lock securely.

Interior storm windows may come equipped with a flange that attaches securely to an existing window frame, and if this is your situation, apply generous coats of butyl caulk around its sides and top for drainage purposes; leave the bottom edge uncaulked so it can drain properly. Shims can help hold bottom expander panels to sill as necessary.

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