A Homeowner’s Guide to Heritage Window Replacement

The Case for Restoration

Many heritage windows are made from old-growth timber. This wood is incredibly dense and rot-resistant, far superior to the quick-growth pine used in many modern off-the-shelf windows today. If the frames are solid, restoration (stripping paint, re-roping pulleys, and weatherstripping) is often more sustainable and keeps the home’s appraisal value high.

The Case for Replacement

Sometimes, history has been unkind, especially when considering Ottawa weather. If you see "soft" wood (structural rot), significant frame warping, or if a previous owner replaced the originals with cheap, ugly inserts, it may be time for a full replacement.

But, before you decide on restoration or replacement, you'll need to determine whether your home is a designated heritage property, or not.

City of Ottawa’s Heritage Register

A public list of over 4,600 properties that the City has identified as having cultural heritage value, even if they aren't officially "designated." Check Classification

Check if your home is on the Register

You can use this tool to determine if your home is a "contributing" heritage building or simply a non-designated property of interest. (click layers icon > zoning) Visit Geo Ottawa Map

Main Heritage Overview

The central hub for Ottawa’s heritage policies, providing the groundwork for how the City protects its historical architecture and neighbourhoods. Visit Overview

Heritage Planning Branch

The professional team of city planners who provide expert advice on restoration, review permit applications, and manage the conservation of Ottawa’s built history. Visit Web Page

Ottawa Property Grant Programs

A matching grant that can reimburse up to 50% of the cost (up to $10,000 for residential homes) for the authentic restoration of original windows, masonry, and other heritage attributes. See Program Status

The greatest "magic trick" of modern window technology is hiding the bulkiness. Historic homes look elegant because their window frames are slim.

Profile: The Architecture of the Frame

The "profile" refers to the three-dimensional shape and depth of the window’s components (sills, sashes, and casings).

• The Heritage Requirement: Old wood windows have deep shadows and intricate "brickmould" profiles. Modern windows are often "flush" or flat. The City requires the new frame to match the exact thickness and "stepped" appearance of the original wood to maintain the building's historic face.
• The Modern Mimic: You can use "high-profile" vinyl or fibreglass frames that are specifically engineered to cast the same deep shadows as traditional wood. Look for sloped, bevelled "putty-line" profiles, vertical/horizontal "butt" joints; you may have to settle for diagonal "welded" corners, which are not period characteristic.
• Be wary of "Pocket" or "Insert" windows. Because this involves putting a frame inside a frame, you'll lose significant glass area. Your windows will look smaller, and your rooms will feel darker. For heritage homes, a Full-Frame Replacement is almost always the better aesthetic choice.

Muntins: The "Bars" of the Window

Muntins are the strips of wood that separate individual panes of glass.

• The Heritage Requirement: The City of Ottawa prefers True Divided Lites (TDL), where each pane is a separate piece of glass. However, they frequently approve Simulated Divided Lites (SDL) as long as they are "permanent"—meaning they are fixed to the outside, the inside, and include a spacer bar between the glass so you can't see through the gap.
• The Modern Mimic: Avoid "Grilles Between Glass" (GBG). These look like flat plastic strips trapped in the window and are the quickest way to make a beautiful home look "cheap."

Operation: How the Window Moves

Replacing a sliding sash with a crank-operated casement is usually a big "no-no."

• The Heritage Requirement: You must match the original mechanical function. If your home has "Double-Hung" (sliding up and down) windows, replacing them with "Casement" (cranking out) windows is usually forbidden. This is because a crank handle and the thick vertical "stiles" of a casement window change the rhythm of the house's exterior.
• The Modern Mimic: Many modern manufacturers make "Hidden Casements" that look exactly like sliding sash windows from the street but actually crank open for better airflow and sealing.

Materials: The Substance

Usually Wood. Clad-wood (metal on the outside, wood inside) is sometimes allowed on non-primary facades. Vinyl is almost universally rejected for heritage fronts.

• The Heritage Requirement: Solid Wood is the gold standard in Ottawa. For "Part V" districts (like Sandy Hill), the City may allow Aluminium-Clad Wood (wood inside, painted metal outside) on the sides or back of a house, but rarely on the front. White vinyl is almost never supported for heritage-contributing properties.
• The Modern Mimic: Fibreglass is the best alternative for non-heritage homes. It can be painted any colour (including dark "heritage" greens or blacks) and doesn't expand or contract like vinyl, allowing for slimmer, more authentic-looking frames.

Glass: Thermal Performance vs. Aesthetics

Double-Glazing for energy efficiency is allowed, but the thickness of the overall sash must remain "slim" to match the original profile.

• The Heritage Requirement: The challenge with modern double-glazing is that it is thick, which forces the wood frame to become "bulky." To keep the window "slim," the City is increasingly interested in Vacuum Glazing (VIG).
• Vacuum Insulated Glazing (VIG): VIG is an advanced glazing solution that creates a thermal vacuum between two thin glass sheets, offering the insulation of triple-pane glass within a single-pane profile. While it is an ideal theoretical solution for retrofitting historic sashes, it is currently unavailable in the Ottawa region. Beyond local supply chain limitations, the technology’s 8mm–10mm profile is extremely sensitive to pressure differentials, requiring specialised engineering that is not yet supported by regional window manufacturers.
• The Modern Mimic: You'll want to use clear, Low-E glass with neutral coatings. Triple-glaze or special energy-efficient dual-glaze glass is becoming the standard. Avoid internal grids, tints and non-clear coatings.

Simulated Divided Lites (SDL)

SDLs do not affect the integrity of a single solid insulated glass unit (IGU) of glass. Mounted on top of the glass, they create a real shadow line that suggests multiple pieces of glass within a sash. From the sidewalk, they are indistinguishable from individual panes.

Putty-Line Detailing:

Modern CNC machining can now replicate the distinct 45-degree "putty" bevel where the glass meets the frame. This creates the sharp shadow lines essential to a historic facade.

Mechanical Joinery:

Traditional PVC or aluminium windows use diagonal welds. New "Timber-Alternative" systems use mechanical butt joints that mimic the vertical-to-horizontal joinery of a master carpenter.

Variable Sightlines:

Instead of one-size-fits-all frames, modern systems use "dummy sashes" and staggered frame depths to ensure that every pane of glass, whether it opens or not, looks perfectly symmetrical.

Aluminium-Clad Wood:

Clean lines, professional look. uses wood on the inside for beauty, powder-coated aluminium on the outside for zero maintenance.

Vacuum Insulated Glass (VIG):

Although not readily available, VIG units are only 6mm to 10mm thick (the same as a single historic pane) but offer the insulation of a 1-inch thick triple-glazed unit. This allows for deep, historic millwork profiles without the "bug-eye" look of thick glass.

Argon & Low-E Coatings:

Modern glass incorporates microscopic metallic layers that reflect heat back into the room. When combined with simulated divided lites (SDLs), you get the look of individual panes with the airtight seal of a single continuous sheet. Note: Some Low-E coatings have a slight tint.

The Triple-Pane Secret

In Ottawa, double-glazing is often not enough. Many of our Martin and Del options allow for triple-pane glass that fits within a heritage-profile frame. You get the look of a thin Victorian sash with the insulation value of a modern wall.

• Maximum U-Factor: 1.22 W/m2⋅K (The rate of heat loss)
• Minimum Energy Rating (ER): 34 (The overall balance of heat loss vs. solar gain)

Martin Windows & Doors

The "Ancestral" line is the gold standard for heritage. They offer genuine wood interiors but use modern weatherstripping and triple-pane options that the original builders couldn't have imagined.

Del (The "Weather Fighter")

Their Bayview line is engineered specifically for our climate, featuring architecturally bevelled frames that mimic the look of traditional wood putty but in a maintenance-free PVC.

North Star

Ideal for "character homes" that aren't under strict heritage designation. They provide the thin sightlines and high-efficiency Zone 3 ratings needed to keep the furnace from running 24/7.