Trim & Finish Carpentry
Window Trim & Casing
The short answer
Window trim is the casing around a window plus the jamb extensions that bring the window frame flush with the wall, and — on a stool-and-apron detail — the sill and the trim beneath it. It is the most common trim work in Calgary right now because window replacement is widespread, and replacement windows almost always leave a deep unfinished reveal that needs new extensions and casing.
Part of our Trim Carpentry service.
The problem new windows create
Window replacement is extremely common across Calgary’s established neighbourhoods, where a great deal of housing stock is now reaching the point where original windows need replacing. The window installer removes the old unit, fits the new one, seals it and leaves.
What remains is a rough opening with a new window sitting somewhere inside it, and a gap between the window frame and the face of the drywall — the reveal. On a wall with modern insulation and exterior sheathing that reveal can be substantial.
Finishing it properly means fitting jamb extensions: pieces of material that bridge from the window frame to the plane of the wall, cut precisely because the depth is rarely consistent across the opening. Then casing is applied over the joint. Doing this well is what makes a replacement window look installed rather than inserted.
The two casing approaches
- Picture-frame casing
- Casing on all four sides with mitred corners, like a picture frame. Clean, contemporary and simpler to execute. Now the more common choice in Calgary, particularly in newer homes and infills.
- Stool and apron
- A projecting sill — the stool — sits on the window opening with a trim apron beneath it, and casing runs down the sides to land on the stool. The traditional detail, appropriate in older homes and where you want a surface to place things on.
- Drywall return, no casing
- The reveal is finished in drywall with a corner bead and no wood trim at all. Minimalist and common in contemporary interiors. Requires a very clean drywall finish because there is no trim to hide anything.
Get a free quote for window trim
We measure, draw and provide a fixed written price — no cost, no obligation.
We reply to every estimate request — usually within one business day.
Casing styles and how they change a room
| Style | Character | Notes |
|---|---|---|
| Colonial / traditional | Profiled, detailed | Matches most Calgary homes built 1980–2005 |
| Craftsman | Flat stock, stepped head, apron sill | Suits bungalows, character homes and infills |
| Modern flat casing | Square, minimal reveal | Contemporary interiors; unforgiving of out-of-square openings |
| Mitred picture frame | Casing on all four sides | Common with vinyl windows that have no sill projection |
| Drywall return | No casing at all | Cleanest modern look; needs a very straight opening |
Why window trim moves in Calgary — and what to do about it
Windows are the coldest surfaces in the house, and in a Calgary January the temperature difference across a window opening is extreme. That gradient drives condensation and dries the surrounding trim unevenly, which is why window casing tends to open at the mitres before any other trim in the house does.
Two details do most of the work. First, glue and pin the head mitres so the joint moves as a unit rather than as two independent pieces. Second, make sure the opening is properly insulated and air-sealed before casing goes on — low-expansion foam in the shim gap, not packed fibreglass, which does nothing for air movement. Trim installed over a leaky opening will keep moving no matter how well it is cut.
On older windows, the sill is often the first thing to fail. Where a sill has cupped or the finish has broken down from sun exposure, replacing the sill and apron while the casing is off is far cheaper than doing it as a separate job later.
What a proper casing job includes
- Checking the opening for square and plumb
- Few openings are either. Knowing by how much before cutting determines whether the casing is mitred or scribed.
- Air-sealing the shim gap
- Low-expansion foam around the frame. This is the difference between a warm window edge and a cold draught behind the trim.
- Glued head mitres
- The joint most likely to open. Glued and pinned, it holds.
- Consistent reveal
- The small setback between the window frame and the casing should be identical on all sides — usually 3 to 5mm. Inconsistency here is the most visible tell of a rushed job.
- Sill and apron detailing
- Where a stool-and-apron detail is used, the horns must be equal and the apron returned at both ends.
Answers
Frequently asked questions
- Do I need new trim after replacing my windows?
- Almost always. Replacement windows sit differently in the opening than the originals, and existing casing rarely fits back cleanly. In most cases the reveal also needs new jamb extensions before casing can be applied. Some window companies include basic trim; many do not, and it is worth confirming what is in your window quote.
- What are jamb extensions?
- Strips of material that bridge the gap between the window frame and the interior face of the wall, bringing the two into the same plane so casing can sit flat. They are needed whenever the window is set back from the drywall — which is nearly always in a modern insulated wall assembly.
- Should I choose picture-frame or stool-and-apron?
- Picture-frame suits contemporary and transitional interiors and is cleaner and simpler. Stool-and-apron suits traditional and heritage homes and gives you a small ledge. Match whichever the rest of the house already uses unless you are re-trimming everything, in which case pick the one that suits the architecture.
- Can you trim a bay or a bow window?
- Yes, though they take considerably more time because of the angled joints and the wider seat board. A bay window seat board is effectively a small piece of joinery and is often built as one, particularly where it will be sat on or used as a display surface.
- What material should window trim be in a basement?
- For basement windows, particularly in egress wells where condensation is more likely, MDF at the sill is a poor choice. A moisture-tolerant material or a solid hardwood stool with a durable finish handles the condensation that forms on cold glass in a Calgary winter far better.
- Should window casing match door casing?
- In almost all cases yes — using the same profile on both is what makes a room read as coherent. The exception is where windows are trimmed with a stool and apron and doors are not; there the vertical casings still match, and only the sill detail differs. If you are updating trim room by room rather than all at once, matching profiles matters more than matching paint, since a slightly different white is far less noticeable than a different profile.
- What is a drywall return, and is it a good idea in Calgary?
- A drywall return wraps the opening in finished drywall with no casing at all, for a very clean modern look. It works, but it is less forgiving here than in milder climates: there is no trim to absorb seasonal movement, so any settling shows as a crack at the corner of the opening, and the drywall edge is vulnerable at a surface that gets condensation. If you want the look, it is worth using a metal corner bead designed for the purpose and accepting that touch-ups are more likely than with casing.
Why homeowners choose us
Careful work, honestly quoted.
We would rather talk you out of the wrong project than sell you one. Everything below is something you can hold us to.
Fixed written quotes
You get a drawing and a fixed price before anything is built — not an hourly estimate that moves.
Built for this climate
Material and joinery chosen for Calgary’s dry winters, so joints stay closed when the humidity drops.
Shop-built, site-scribed
Components made in a controlled shop, then scribed to your actual walls rather than trimmed to hide gaps.
One point of contact
The person who measures your space is the person accountable for the finished work.
Where we work
Calgary Carpentry serves Calgary and the surrounding communities.
Thinking about window trim?
Send a few details and we will come and measure. Free, no obligation, and a fixed written price.
We reply to every estimate request — usually within one business day.