Installing a fixed window means removing the old unit, preparing the rough opening, setting the new window in place, shimming it level and plumb, then sealing and insulating the perimeter. For a standard same-size replacement in a wood-frame wall, the whole job takes two to four hours. Because fixed windows have no moving sashes or hardware, they are one of the simpler window types to install — but the air sealing and flashing sequence must be done right, or the performance gains from the glass won’t matter.
Fixed windows are sometimes called picture windows, though the two terms have subtle technical differences — if you want to dig into that, see our guide on fixed vs picture windows.If you want to explore the full range of non-operable options, the picture window replacement page covers sizing, glazing choices, and pricing in detail. Either way, no operable parts means no hinges, operators, or weatherstripping to align. What you do need to get right is the rough opening prep and the moisture management around the frame.
Tools and Materials You’ll Need
Running to the hardware store mid-install on a cold Ontario morning is a situation worth avoiding. Gather everything before you start:
- Tape measure and 48″ level
- Pry bar and utility knife
- Cordless drill with 3″ exterior wood screws
- Composite or cedar shims
- Low-expansion foam (window and door rated)
- Self-adhesive flashing tape
- Exterior-grade silicone caulk
- Safety glasses and work gloves
Buy the window before you buy anything else, and confirm the rough opening dimensions match. Most manufacturers require 1/2″ of clearance on all four sides between the window unit and the rough opening frame.
How to Measure the Rough Opening
This is the step that determines whether the window fits or doesn’t. Measure the rough opening width at three heights — top, middle, and bottom — and the height at three widths — left, centre, and right. Use the smallest number in each direction.
For wood-frame construction, the rough opening is typically 1″ wider and 1″ taller than the listed window size. For masonry or brick openings, tolerances are tighter. You’ll also need to confirm that the lintel above is structurally sound before cutting anything.
Write down your measurements and check them twice before placing an order. A window that’s even 1/4″ too wide means cutting into the framing — a mistake that costs more to fix than the window itself.
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Removing the Old Window
Score the interior and exterior caulk lines with a utility knife first. Work slowly near drywall and brick mould to avoid damage you’ll have to repair later.
From inside, pull off the interior trim and stops. Then push the old unit outward, with a helper supporting it from outside if it’s a large unit. Scrape all old sealant, foam residue, and debris off the rough opening surfaces. If you find any rot, mould, or water-damaged framing at this stage, repair it before the new window goes anywhere near the opening. Installing over damaged framing just seals the problem in.
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Step-by-Step Installation Process
Once the opening is clean, dry, and square, work through the installation in this order:
- Apply flashing tape along the rough opening sill, lapping up both sides by at least 6 inches. This creates your first layer of water protection.
- Set the window unit into the opening from outside. Rest it on the sill temporarily while you check position.
- Place your level on the sill and both jambs. The unit must be level, plumb, and in the same plane as the wall.
- Insert composite shims at the corners and mid-spans to hold the window in position. Shims should support — not compress — the frame.
- Drive 3″ screws through the nailing flange or installation holes into the rough opening framing. Pre-drill to avoid splitting the wood.
- Re-check level and plumb after fastening. Small shifts happen, and this is the last chance to correct them.
- Apply flashing tape over the nailing flange, starting at the sill, then the sides, then the head. Each piece laps over the one below — follow the direction water travels.
- From inside, fill the gap between frame and rough opening with low-expansion foam. Apply it in a single continuous bead and leave it to cure before trimming.
- Trim the cured foam flush, then install interior trim.
- Apply exterior silicone caulk where the brick mould meets the cladding. Tool it into a clean, sloped bead that sheds water outward.”Builders often rush the rough opening prep, but it’s the most important part of the job. If the framing is out of square by more than a quarter inch, you’ll fight the window all the way through the install — and you’ll still end up with seal problems five years down the road.”— Marcus Reid, Building Envelope Consultant, Hamilton, Ontario (20 years in residential construction)
Rough Opening Size Reference
This table shows standard rough opening dimensions for common fixed window sizes. Always confirm against your specific manufacturer’s installation guide, as tolerances vary by product line.
| Nominal Window Size | Rough Opening Width | Rough Opening Height |
| 24″ × 36″ | 25″ | 37″ |
| 36″ × 48″ | 37″ | 49″ |
| 48″ × 60″ | 49″ | 61″ |
| 60″ × 72″ | 61″ | 73″ |
| 72″ × 84″ | 73″ | 85″ |
Fixed Windows vs Other Window Types
Not every opening calls for a fixed unit. Here’s how fixed windows compare to the most common alternatives. You can also explore types of sliding windows and replacement casement windows to see which configuration fits your wall:
| Feature | Fixed Window | Casement Window | Slider Window |
| Ventilation | None | Full sash opening | Partial opening |
| Energy efficiency | Excellent | Very good | Good |
| Installation complexity | Low | Medium | Low–Medium |
| Egress compliance | No | Yes (min. size) | Yes (min. size) |
| Best suited for | Views and light | Bedrooms, kitchens | Wide or low openings |
For areas where ventilation isn’t required but light is the priority — a stairwell wall, a high gable end, or a living room feature — fixed window replacement is often the right call. Many GTA homeowners also combine a central fixed unit with flanking openers, pairing it with replacement casement windows on either side to get both light and airflow in the same wall section.
Insulation and Air Sealing
This is where most DIY installs fall short. Low-expansion foam is not interchangeable with standard expanding foam. General-purpose foam generates too much outward pressure on a vinyl frame, which bows it slightly — enough to break the glass-to-frame seal and cause air leakage along the edges.
Apply the foam in one bead around the full perimeter gap and let it cure fully before trimming. Don’t pack it in or apply it in multiple passes.
On the exterior, the flashing sequence matters because it mirrors how water moves. Sill first, sides second, head last — each layer laps over the one below. Reversing this sequence, or running caulk over flashing tape instead of the other way around, creates pathways for water to travel inward behind the tape.
ENERGY STAR™ certified windows already carry Low-E coatings and insulating gas fills that reduce heat loss significantly. But even the best window performs poorly if the air sealing around it is incomplete. The window and the installation work as a single system.
“I’ve assessed hundreds of homes with condensation and heat loss problems — homes that had perfectly good windows installed in them. The issue was almost always the installation: foam gaps, wrong flashing sequence, or caulk applied over tape instead of under it. The product rarely fails. The process does.”
— Sandra Kowalczyk, Certified Energy Advisor, Mississauga, ON (HERS-rated home assessments since 2011)
Ontario Building Code Considerations
Ontario Building Code (OBC) Section 9 applies to window installations in residential buildings. A few points that directly affect fixed window installs:
- Fixed windows do not satisfy egress requirements in sleeping rooms
- Bedrooms require at least one openable window with a clear opening of 0.35 m² and a minimum dimension of 380 mm on any side
- Replacing an openable window with a fixed unit in a bedroom may put you offside with OBC — confirm before ordering
- ENERGY STAR™ certified windows meet or exceed OBC thermal performance thresholds for Climate Zone 6, which covers the GTA and most of Southern Ontario
- A building permit is usually not required for same-size, same-location replacements, but structural changes or egress modifications do require one — confirm with your local municipality
When to Hire a Professional
A straightforward same-size fixed window replacement in a wood-frame wall is manageable for a capable DIYer. But certain situations call for a professional installation crew:
- Units larger than 60″ in any dimension, which require two people and proper support rigging
- Masonry or brick openings needing lintel assessment
- Any rot, mould, or structural damage discovered in the rough opening framing
- New openings cut through load-bearing walls
- Combination configurations with stacked or adjoined units
TotalSeal’s certified installation crews handle all of these scenarios across the GTA. Whether you’re looking at window replacement in Scarborough, window replacement in Brampton, or window installation in Etobicoke, every install follows a defined workflow built around building code compliance and airtight results. A free in-home consultation sets clear expectations before any work begins.
Frequently Asked Questions
Do I need a building permit to install a fixed window in Ontario?
Replacing a window of the same size in the same location typically does not require a permit in Ontario. Any structural change to the opening, or a change that affects egress compliance, does. Confirm with your local municipality before starting.
What foam should I use around a fixed window frame?
Use low-expansion polyurethane foam rated specifically for windows and doors. Standard expanding foam applies too much outward pressure on the vinyl frame, which can distort it and compromise the seal between the frame and glass unit.
Can I replace an openable window with a fixed window in a bedroom?
Not without checking egress compliance first. Ontario Building Code requires bedrooms to have at least one openable window with a minimum clear opening of 0.35 m². A fixed window does not satisfy this requirement.
How do I know if my fixed window seal has failed?
The clearest signs are foggy or cloudy glass between the panes, condensation on the interior glass surface, cold drafts near the frame, or water staining on the sill or surrounding wall. Any of these indicate the insulated glass unit needs replacing.
How long does a professionally installed fixed window last?
A quality ENERGY STAR™ certified vinyl fixed window, properly installed and sealed, typically lasts 25 to 35 years in Canadian climates. Frame integrity, glass seal quality, and the standard of the original installation are the main factors that determine service life.
