The windows in my 1970s split-level were the definition of builder-basic: drywall returns, skinny casing (or none at all), and that slightly unfinished look you only notice once you can’t unsee it. The good news is you do not need a historic home or a fancy millwork catalog to get that solid Craftsman vibe. With flat-stock boards, a simple stool, and an apron, you can make an ordinary window look custom in a weekend.

This guide walks you through measuring, cutting, and installing thick, flat trim around a drywall-return window, plus the little details that make it look intentional instead of “I added boards to a window.”

A real interior room with a plain window upgraded with thick flat-stock Craftsman trim, including wide side casings, a substantial top piece, and a stained wood stool with a painted apron

What gives it the Craftsman look

When people say “Craftsman trim,” they usually mean a few specific proportions:

  • Flat, square-edged boards instead of ornate profiles
  • Thicker casing (commonly 1x4, 1x5, or 1x6 depending on the room)
  • A strong top piece across the window, sometimes built up to read like a header
  • A stool and apron at the bottom that gives the window a grounded, built-in feel

It is clean, confident, and forgiving. If your walls are not perfectly straight (welcome to real life), Craftsman trim gives you enough visual weight to hide small sins with caulk and consistent reveals.

Before you start

Drywall return vs. wood jamb

This tutorial is for a drywall return window, where drywall wraps into the opening and meets the window frame. That is common in many newer builds and remodels, although details vary by builder and region.

What you are doing is adding casing on the wall face, plus building a stool that either butts to the window frame or slips slightly under it (depending on your window style).

Quick safety note for older homes

If your home is from the 1970s (or older), assume there is a chance you will run into lead-based paint on old trim or in layers of repainting. Before you start scoring, sanding, or scraping, use lead-safe practices: contain dust, wear a proper respirator, and consider a test kit or a pro if you are unsure.

Should you fix drafts first?

If you already know the window is drafty, handle the air sealing before you bury gaps behind pretty trim. For quick DIY draft fixes, see Weatherstripping vs. caulking for drafty windows. If your window is sticking or swollen, that is worth addressing too so you are not fighting it after the trim is installed.

Tools and materials

Tools

  • Tape measure and pencil
  • Speed square (or combination square)
  • Level (2 ft is fine)
  • Miter saw (for accurate square cuts) or circular saw with a guide
  • Brad nailer (18 gauge) or finish nailer (16 gauge), or a hammer and finish nails
  • Oscillating multi-tool or sharp utility knife (for cutting paint lines)
  • Stud finder (helpful, not mandatory)
  • Caulk gun
  • Sanding block or 180 to 220 grit sandpaper

Materials

  • Flat-stock casing: 1x4, 1x5, or 1x6 (paint-grade primed finger-jointed pine is friendly for DIY)
  • Stool: 1x4 to 1x8 depending on how deep you want it, or 5/4 stock if you want a thicker sill
  • Apron: typically same width as side casings, or slightly wider
  • Wood glue (optional but useful for stool returns)
  • Wood filler or spackle (painted trim) or stainable filler (stained stool)
  • Paintable caulk
  • Shims
  • Nails: 1 1/4 in to 2 in is common for most casing work; longer nails (up to 2 1/2 in) are typically for thicker stock into framing, and you should use extra care around wiring and plumbing

Picking board width (my quick rule)

  • Small rooms or tight walls: 1x4 casing looks clean without feeling bulky.
  • Most living spaces: 1x5 is a sweet spot that reads “custom” but not heavy.
  • Tall ceilings or big windows: 1x6 looks right, especially if your baseboards are 5 inches or taller.

Material choice near windows

If you get condensation on your windows, avoid MDF for stools or any trim that will sit in the splash zone. Solid wood, primed finger-jointed pine (painted), or PVC/composite trim tends to hold up better in damp climates and bathrooms.

Plan your layout

I am big on “measure twice, cut once,” but with trim it is more like “measure, mock it up, then cut.” Here is the order that keeps you out of trouble.

1) Pick a reveal

A reveal is the little step-back from the window frame to the inside edge of your casing. On many windows, a 1/8 inch to 3/16 inch reveal looks crisp. The goal is consistency more than a magic number.

2) Check for out-of-square

Measure the window frame height on the left and right. Then measure the width at the top and bottom. If things vary, plan your trim layout so your reveals stay even. Drywall returns love to be slightly wonky.

3) Decide the top: simple or built-up

To keep the language consistent, here is what I mean in this article:

  • Top casing: the horizontal board across the top, same thickness as the side casings.
  • Header cap: an optional wider board above the top casing that makes the top look more like a Craftsman header.

4) Decide stool depth and ears

Stool depth is what makes this look built-in. A solid starting point is:

  • Depth: window frame to room side plus 3/4 inch to 1 1/2 inches
  • Side overhang (ears): 3/4 inch to 1 inch past the side casings

You can go bigger, just stay consistent throughout the room.

A window bottom showing a wood stool with squared corners and small side returns above a flat painted apron and thick flat-stock side casings

Install the trim

Step 1: Prep and protect

  • Score old caulk or paint lines where existing trim meets the wall.
  • Patch obvious drywall damage and sand it flat.
  • If you are working over a finished floor, put down a drop cloth. Trim projects generate little brad nails that love bare feet.

Step 2: Install the side casings

Cut two side casings with square ends. Dry fit them with your chosen reveal. Use a level to make them look plumb. If the window frame is slightly out, you can cheat a hair to keep the trim looking straight to the eye.

  • Shim behind the casing if the wall dips.
  • Nail near the outside edge into studs when possible.
  • Add a few nails closer to the window opening to keep it tight to the drywall return area.

Simple nailing pattern

For most interior casing, aim for nails about every 12 to 16 inches, plus one within a couple inches of each end. Put the longer nails on the outside edge where you are most likely to catch framing. Avoid nailing so close to the window frame that you risk hitting hidden hardware or deforming the frame.

Tip from my own mistakes: Do not force a bowed board flat with nails. It will fight you and usually opens gaps later. Swap the board or add shims so it sits naturally.

Step 3: Install the top casing (and optional header cap)

Simple top: Measure between the outside edges of the side casings (or follow your preferred butt-joint layout), cut the top casing square, and install it with the same reveal.

Built-up top: Install the top casing first, then add a wider header cap above it. That one extra board adds a lot of Craftsman character without getting fussy.

Either way, step back and eyeball it from across the room before you lock it in. This is where small alignment tweaks pay off.

Step 4: Build and install the stool

The stool is the part that changes the whole vibe. Here is an approachable way to do it with straight cuts and a clean fit.

When you might need an extension jamb

If your window frame is recessed and you do not have a flat, solid landing to support the back edge of the stool, you may need an extension jamb (a liner) first. In plain terms, you are creating a flush surface so the stool can sit tight and look intentional.

Measure stool length

Stool length is typically the inside window frame width plus your side overhangs (the ears). A common ear is 3/4 inch each side, so you would add 1 1/2 inches total.

Measure stool depth

Depth is measured from the window frame out onto the wall. If you want the stool to feel substantial, do not be afraid of 5 1/2 inches or more in a main room. Just keep it consistent across windows in the same space.

Cut the stool notch (if needed)

Some windows have a frame that sits proud of the drywall return, and a stool looks best if it notches around the frame so it tucks in. Hold the stool stock in place and trace where it hits the window frame, then cut the notch with a jigsaw or oscillating tool. Dry fit until it drops in without forcing. You want snug, not jammed.

Add stool returns (optional)

If your stool extends past the wall opening, add small return pieces on each end to cap exposed end grain.

  • Cut two small return blocks the same depth as the stool projection.
  • Glue them to the stool ends and pin them with brads.

Let the glue set before you start handling it a lot.

Install the stool

Set the stool in place, shim if needed so it does not rock, then nail it down into framing where possible. If you use construction adhesive, use a thin bead. Too much can telegraph, and it can make future service a mess.

Step 5: Install the apron

The apron is the board under the stool. Cut it so it aligns with the outer edges of your side casings, or make it slightly longer for a bolder look.

Hold it tight to the underside of the stool and nail it off. If there is a gap because the stool is not perfectly flat, shim behind the apron or pull it tight with nails and then caulk the seam.

A homeowner using a brad nailer to attach flat-stock casing to the wall beside a window with drywall returns

Finish it clean

Fill and sand

  • Fill nail holes with wood filler.
  • Let it dry fully, then sand smooth.
  • Vacuum or wipe off dust so paint sticks.

Caulk the right seams

Caulk where trim meets drywall, and where the apron meets wall. Use a paintable caulk and keep it neat.

Skip caulk on wood-to-wood joints you want to look crisp (like stool to side casing) if you are staining or if you want shadow lines. If everything is painted, you can caulk those lightly, just do not overdo it. Too much caulk rounds corners and kills that sharp Craftsman look.

Prime and paint (or stain the stool)

For painted trim, prime any raw wood and spot-prime filled areas. For a stained stool with painted casing, stain and clear coat first, then paint the surrounding trim.

If you want to reduce condensation issues that can mess with finishes around windows, it helps to understand why it happens. I broke that down in Why windows sweat in winter and how to stop it.

Common problems

My opening is not square and my reveals wander

Prioritize a consistent reveal against the window frame, not the drywall edge. If the drywall return is wavy, your casing can bridge it. Use shims and caulk to make the wall side look clean.

The casing rocks because the wall is bowed

Shim behind the casing at nail points. If the bow is severe, you may need to plane the back of the board slightly, but shims solve most real-world walls.

I cannot hit studs where I need nails

This is common around windows, especially near corners. Use longer nails where studs exist, and add more nails where they do not. Construction adhesive can help, but use it sparingly so future removal is not a drywall disaster.

Gaps where stool meets the window frame

Small gaps can be caulked if you are painting. For stain-grade work, take more time on the notch fit and consider using backer material or a thin scribe strip if the frame is irregular.

Craftsman-style options

  • Add a backband: If you want more depth, add a thin strip around the outside edge of the casing. Keep it simple and square.
  • Thicker top piece: Use 5/4 stock for the top casing or header cap to create a subtle built-up look.
  • Wider apron: A wider apron reads more traditional and helps balance tall windows.
  • Match your baseboards: If your baseboards are chunky, your window trim should be too, or the room can look mismatched.

When trim is not the fix

Trim makes a window look better, but it will not fix a window that is failing, fogged, or rotting. If you are debating whether to dress it up or replace it, skim 7 signs it’s time to replace your home’s windows. Sometimes the smartest DIY move is putting your effort into the right window first, then trimming it out once.

Quick FAQ

Do I need to remove the drywall return?

No. The casing installs on the wall surface outside the opening. The stool can be fit to the window frame without tearing out the returns.

What wood should I use?

For painted trim, primed finger-jointed pine is budget-friendly and stable. For a stained stool, use clear pine, or hardwood like oak if you want durability and a richer look.

How wide should the casing be?

In most homes, 3 1/2 inches to 5 1/2 inches (1x4 to 1x6) looks right. Choose based on ceiling height, window size, and how beefy your baseboards are.

Can I do this with basic tools?

Yes. A miter saw is nice, but you can make square cuts with a circular saw and a guide. The key is accurate measuring and patient dry-fitting.