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How to Install Window Trim

How to Install Window Trim

Hi everyone, I’m Cristina from Remodelando la Casa, and I’m beyond excited to join the team of Pretty Handy gals and guys!  I’m still pinching myself at such a wonderful opportunity.

Today I’m going to show you a fairly easy way to transform your builder grade windows from plain and boring to beautiful with loads of character and with a more finished appearance.

trimmed left window lg

Right now I’m working on updating my bedroom, where I have a couple of these windows.

small window sills lg

 They look  like they are wearing skirts, but forgot to put on the tops! 🙂  Yeap, naked!

plain builder's windows lg

Let’s change that by dressing up those windows!

This is only a decorative treatment.  All the wooden material (Poplar or Pine), can be found at your local home center.

(Affiliate links are included for your convenience. Brittany earns a small percentage from a purchase using these links. There is no additional cost to you. You can read more about affiliate links here.)


How much material you need depends on the size of your window, but this is what I used:

parts of window - trim
moldings for window trim


The first thing to do is getting rid of the old window stool and apron.
Using the utility knife, score around the window cutting the caulking. This is very important to prevent rips in the drywall.

Cutting the caulking lg

 Using the pry bar begin lifting the apron, use a wood shim as support to prevent damage to the wall.

pray bar to take away sill lg

 Once the apron is off, you can begin lifting the stool.

taking away window sill lg

Underneath I found lots of wood shims that were used to level the stool.  They were left in place.  Scrape the old caulking from the window and wall.

window sill removed lg

Don’t throw away the old window stool, you can use it to trace the pattern onto your new stool.   Measure the width of your window, add the width of both side casings: 7 inches, add 1/2″ for reveals (1/4″ on each side) and add 2 more inches for the “horns” (The horns are those extra parts on the window stool that go beyond the apron. Allow one inch on each side of the stool.)

Mark the center on the old and new stool boards, align those centers and trace the new pattern.

tracing new stool with old one lg

If you are working on more than one window, it is a good idea to mark each board, even though they look pretty much the same, their measurements can vary.

two window sills ready to be cut lg

Use your jig saw to cut away those marked ends.

Cutting window stool with jig saw lg

Place it on the window and make sure the new stool is level.  Nail it in place.

nailing stool to a window

The apron can be installed by centering it underneath the stool.  The dimensions are the same as for the stool, but without the horns (2″).  As shown below, the horns protrude an inch on each side beyond the apron.

attaching apron to a window lg

The side casings can be installed now.  To figure the length of the side casings, measure the distance from the stool to the top of the opening of the window, add 1/4″ for reveal line. Secure the side casings with nails.

attaching sides of window lg

After the side casings are installed, measure the distance from the outer edges of the side casings. That will give you the head casing length.

Head Casing Length

Nail the head casing in place.

attaching top part on window lg

 Cut the decorative molding, crown and half round.

crown molding and half round to trim window lg

When cutting the decorative molding, miter the ends (cut at a 45 degree angle as shown below.)  Remember to cut the molding upside down.

cutting crown for window lg

The crown is installed at the very top of the head casing and the half round is attached to the bottom of the head casing.

nailing crown molding to window lg

The returns (side pieces of the decorative molding) are glued in place and held overnight with tape.

attaching returns of crown to window lg

Fill the nail holes and gaps with caulking. After the caulk is dry, a good sanding is a necessity.  Don’t forget to sand those sharp edges too.

sanding window before painting lg

 Paint the trim with one coat of primer and two coats of paint. Then you’ll have good looking windows in your room!

new trimmed window1 lg

Add new paint in a contrasting color on the walls and the room is almost ready!

new window trim-crown lg

 I had some leftover paint that I mixed to achieve this hue.

trimmed left window lg

window stool lg

These twin windows really add a lot of character to the room.

finished two window trims lg

 The trim makes a big difference, wouldn’t you agree?

new trimmed window2 lg

 Thank you so much for having me here at Pretty Handy Girl! I can’t wait to share more with you!

~ Learn more about Cristina~

Don’t miss Brittany’s great tutorial for trimming a casement window: How to Install Trim and Casing Moulding on a Casement Window by PrettyHandyGirl

112 replies
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  1. Tina
    Tina says:

    We ordered beautiful moldings in molding creator, increadible moldings of houses, facades, I really recommend them because they are of a very high level of services.

  2. Ryan
    Ryan says:

    I’m looking to replace the old wood trim around my wood windows. At the moment window, trim, stool, and apron all match but I was looking to update with the white trim that is used throughout the house. My question is this…can I remove the stool/apron and just have the trim?

    I know it would leave a gap and I would hate to try and sand, stain, etc. the windows to match a new piece of wood where the stool would have been. Right now I am considering removing the current trim, cutting the current stool flush with the wall, and then adding the new trim around the window and cover the cut surface of the old stool.

    Would this work? What is your advice? Please help!

  3. David Stanley
    David Stanley says:

    in some of the pictures I see blinds. In the final picture I do not. I am going to keep blinds in my windows once I am done with the trim.

    How would you recommend I “cover” up the bulky top of the blinds so as to keep my windows looking neat and clean? Thank you!

    • Jennifer
      Jennifer says:

      I’m following this as I have the same question as David. I want to leave up my blinds to retain privacy, but I don’t want to see the top of the blinds. Do you just install the Head Casing lower?

    • Brittany Bailey
      Brittany Bailey says:

      Jennifer and David, Cristina took down the blinds at the end. But, you can certainly install them inside the window as you saw in her earlier pictures. To cover the top, you’ll need to add a fabric valance or get creative with a wood slat. You can also leave it exposed as she had.

  4. Xavier
    Xavier says:

    Very nice indeed
    2 quick questions:
    1) did you use glue – or at least caulk – underneath each piece of wood, or nails only?
    2) Why you didn’t install the side casing aligned with the flange of the wall? looks like you left a 1/4″ gap


  5. Rob
    Rob says:

    I have never done a window trim job or anything like it, but gave it a shot last year when the windows on my 15 year old home started to look like junk around them (only a stool and apron and no other trim…began cracking, and such). Your directions were great. The look is very simple, yet elegant. Thanks a bunch. The only challenge I had with your instructions was where you said to cut the molding at a 45 degree angle…to make it work on the style of molding you chose, the mitre saw angles you set are actually a bit different…don’t have them handy now, but you can look them up anywhere.

  6. Amy
    Amy says:

    Hi! Where did you buy your half rounds? I went to Home Depot and Lowes and neither one carried them. Thanks!

  7. Jenny
    Jenny says:

    Hi! I know this post is a few years old. I hope you are still able to reply to this.

    I am starting this project soon. I have a question that I didn’t see posted yet. What do you mean by REVEALS? It says to add 1/2 inch for reveals but I’m not sure what is being revealed?!?

    Thanks soooo much!

    • Brittany Bailey
      Brittany Bailey says:

      Jenny, the reveal is the portion of the stool that sticks out beyond the window casing. You’ll see the side casings sit on the stool, but the stool extends out an additional 1/2″ on each side (that’s the reveal.) Hope that helps.

  8. Jay
    Jay says:

    I’ve been looking at doing this but I have seen over and over to remove the drywall return and replace that with a wood jamb instead of leaving the drywall return due to cleanliness of the lines. Did you leave the drywall return? It looks like you did leave the existing return in there and just used the outside trim pieces. I was curious about any spacing issues you may have had as this would save a lot of time in trimming the window without havingto remove the drywall and replace it with wood.

    • Jason
      Jason says:

      I’m hoping to hear the answer to this as well. People I’ve talked to have also said I’d need to remove the drywall and replace it with a wood jamb. Did you do this? I too would love to avoid removing the drywall and instead just trim around the outside of the window as it is, but I worry about how it would look without a jamb. Thanks!!

      • Brittany Bailey
        Brittany Bailey says:

        From Cristina Jay and Jason: I’m so sorry for my late reply! The drywall return on my windows was left in place. As I mentioned in my post, this is only a decorative treatment. The right way to trim this kind of window would be by first getting rid of the drywall returns, install a jamb and them add the outside trim. I didn’t have spacing issues doing it, they had sharp straight lines which was the main reason for me to leave the returns, well avoiding the drywall mess was another good reason. 😉 This would be like a “jamb cheating option” on this kind of window trim.

  9. Ashley
    Ashley says:

    Question for you: Is the inside of your window wood or drywall? If it’s drywall did you paint it white or the same color as the window trim? I’ve been having a time trying to find the answer to that question :/

    • Brittany Bailey
      Brittany Bailey says:

      Ashley, do you mean is the window wood or vinyl? Our window is vinyl and no I didn’t paint it. The trim I installed around it is all wood and yes, I painted it all the same color (but you can’t tell that the vinyl isn’t painted.

    • Brittany Bailey
      Brittany Bailey says:

      Ashley, this is from Cristina: Ashley, I’m sorry for my late reply! The inside of my window, the returns are drywall. I painted them the same color as the window trim , a semi-gloss Swiss Coffee color.

      • Steve
        Steve says:

        I kept the inside of my window as drywall as well, but I applied all-purpose joint compound over the drywall with a putty knife to cover the texture. The result is that you can’t even tell the inside of the window is not wood trim.

  10. Michele
    Michele says:

    I FINALLY got every window and doorway in my home trimmed out. I absolutely could not cut that angle on the half round moulding — it kept splitting it. The only half round available in my local area was oak, which is VERY hard, and cutting that short piece with the angle on one side was too much for the wood. I ended up having to have flush ends on the half round. It still looks awesome…..but I still miss the little accent that could have been if the half round had wrapped around the casing. My miter saw blade was probably too thick or too dull for it.

    • Brittany Bailey
      Brittany Bailey says:

      To Michele from Cristina:
      I’m so sorry for not answering before! Wow, you were on a train, I bet they look great! Most of the time the miter saw blade is too much power for those tiny pieces of trim. A miter box is a good option when making those small cuts.


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