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Home Improvement: Trimming a Window (replacing the sill & apron, adding side/top molding)

Home Improvement: Trimming a Window (replacing the sill & apron, adding side/top molding)

When we moved into our new house back in April, I had a list of must-do items that I wanted to do to help “improve” the house.  And make it more OUR home.  In my brain, I figured, “hmmm, these few projects should only take a month or so…….maaaaaybe 2 months”.

Ha!  That was the clueless Ashley talking.  You know, the girl who has no-idea-what-she’s-talking-about-because-she’s-never-purchased-a-home-before……or-renovated-one-for-that-matter.  Silly.  Just, plain silly. :)

I have learned that when one project is underway……17 more projects suddenly appear.  Like, when we began laying new hardwood floors, we realized that we’d better buy those new baseboards we had been eying.  But before the baseboards could be nailed in, we needed to trim out all the doors.  But that’s funny…..because you have to replace the doors first (with the ones you want) before you can trim them out.  But hey, don’t forget that painting the walls would be easier if you did it before installing your brand new doors.  Oh yeah, but don’t go installing those new doors when painting them first would save you a lot of grief.  Can you see the rookie thought process in all this?

Yeah…..we’re learning.

And have made lots of progress.

But I can’t wait to actually lay around and enjoy all this work.  Go on……..someone please lie to me and tell me that this day will come! ;)


Until then…….our latest love.  Trimming out windows!!!

**Nope, baseboards still aren’t up.  Just pretend they are. ;)


Trimming out these windows (and our doors) has been magical.  All of the sudden, our boring ol’ windows are turning into stunning little focal points.

A piece of wood here and there, a few little pieces of molding……done.  We are loving how it’s all turning out.

And we love that our windows are no longer nekked!


We’re kinda cheater-pants because we’re not trimming out the interior edges of the windows.  We’re just painting the interior edges of the windows the same color as the trim.  A little deception is okay in this scenario. :)


And because I love seeing a good BEFORE/AFTER shot……I went digging in my old photos.  But turns out, I didn’t really focus much on this particular window and its surroundings.  But here’s a picture where you can see it in the background.  You know, just to get an idea of how that window used to look in the living room.


See ya later sucker!

Because here she is NOW!

I keep sneaking into the rooms that are mostly done, and I just stare.  Watching these projects actually turn out…… THRILLING! :)

More to come soon…


But would you like to see how we trimmed out our windows?

Most likely, your window is a little bare.  It probably has a window sill and a measly little apron down below.  A very common window construction.

Let’s fix that.  Pronto. :)

**Wood sizes and trim styles are totally variable.  I will show you the process we used and the material we used…….but keep in mind, but you’ll have to decide what wood widths and trim styles look best in your home.


Here are the wood types we purchased and used.

  • 7.5 inch wide MDF (along the top and for the sill)
  • 2.5 inch wide MDF (for the sides and the apron….which is below the sill)
  • 1 1/2 inch MDF molding piece for upper trimming
  • 1/4 x 1/2 inch wood piece for upper trimming


And then, here are a few more supplies you’ll need:

  • Nail gun (you could also do this by hand…..but a nail gun will save you some time)
  • Liquid Nails (construction adhesive)
  • Paintable Caulk
  • Miter Saw (or a miter box to cut molding pieces at a 45 degree angle by hand)
  • Utility Knife
  • Crowbar
  • Paint Scraper


Okay……let’s do this!

First, use a utility knife to cut the old caulk seams…


And then pry up the old wood with a crow bar of some sort.


Scrape off all the old caulk and any other debris that’s hanging around.


Now, measure the opening of your window base.  Write that number down.  (Ours is 28 inches wide.)


Then, decide how wide you want your window sill to come out.  For our windows, we use 2.5 inch wide pieces along the vertical sides of the window.  But we like the sill to come out an inch beyond that.  So, we measured out 3.5 inches at both sides and added both of those measurements to the window width measurement.  (So……28 + 3.5 + 3.5 = 35 inches)


Then measure the depth of the window.  Write that number down.


Then, decide how deep you need your sill piece to be.  Our window was a little over 5 inches deep……so we decided to use 7.5 inch wide MDF for the sill.  We have other windows that are only 3.5 inches deep…….so a piece of 5.5 inch wide MDF works great for those.  It just depends, so measure and decide what will look the best.

Now, grab the board you are using for your window sill and cut it down to the length you need it.  In our case, 35 inches long.  Then, use those measurements that you wrote down and draw them right onto your board.


Be sure to measure both sides and mark them separately…..because most likely, they are a little different.  Yeah, no one’s house is perfect.


Then, use your saw of choice and cut those pieces out of your board.


Then, place the board in the window opening.  If it’s slightly off, make adjustments until it fits.


Now, nail the board into place, securing it to the stud pieces underneath.


Now, it’s time for the top piece.  Cut it to the width you need.  In our case, it was the window width plus 2.5 inches on both side for the vertical pieces that will be added next.  (You can add the vertical pieces first but we needed our top piece in place first, because it’s slightly hiding some of the blinds behind it.  And it was hard to measure where that top board would sit, without having it in place first.)  Use a level to be sure that the top board is sitting evenly.


And then nail it in place.


Next, measure how long your side pieces need to be and nail them in place as well.  (Measure them independently.  Most likely, they will be different lengths.)

Now, measure for your apron piece.  Measure from one side piece to the other…….because you’ll want it to be the exact same width so that everything looks even.

Then, nail that apron right in place.


Now, for everything up until now, we used 2 inch brad nails.  But for the trim pieces, you want something much smaller.  We used little half inch brad nails.


For the upper trim piece, we decided on a 1.5 inch wide simple molding (another close-up picture above).  I have seen much bigger and more ornate molding pieces used…..but I prefer a simple molding for the window.

Just measure the width of your board that’s in place, grab your molding piece and miter the two ends at a 45 degree angle to meet the length measurement you need.


And then nail it in place, using those smaller nails.


And because I need a close-up of everything, here’s that 45 degree angle.


Oh, and line up the top of the molding evenly with the top of the board piece.


Then, cut a “return” piece, that is mitered (at a 45 degree angle) at one end and then a straight 90 degrees at the other, to sit against the flat wall.  Nail it in place.  (And don’t worry if it’s not perfect……we’ll fill in the cracks later.)


If you get into a tight spot and can’t fit a nail gun or hammer, construction adhesive works great and dries really fast.  (Just don’t get it on your skin.  It’s awful to get off!)


We like liquid nails.  And use it for many things.


Next, nail the skinny trim piece in place.


Keep the trim piece even with the bottom edge of the board behind it.


And because this trim piece is flat (unlike the curvy molding piece), you can just butt up the corner pieces to each other.  (Don’t worry, we’ll fill in those cracks later.)


Now, time for all the finishing work (…which always turns out to be my job!)

Use wood filler and fill in all those nail holes.


Once it’s dry, sand it down evenly.  And while you’re at it, smooth out any other wonky edges or rough corners.  (The MDF we used has a slight curve to it along its edges.  So, any edges that we cut, we tried to match the same curved edge look.  You may want to do the same.)


Once you’re done sanding, vacuum up as much as possible.  Then wipe with a damp cloth to get all of that dust off and then let dry.  However, if you don’t want to wait for the wood to dry (after wiping it with a damp cloth), using denatured alcohol on a cloth will make the cloth damp enough to attract the dust but dries instantly.


Now, time for the fun.  Caulking.  Begin caulking all your cracks and gaps, hiding any imperfections.  I’m serious……this stuff is magic! :)  (Just be sure you’re using paintable caulk.)


But here’s my secret.  A bowl with a bit of water and some wet paper towels.  ALWAYS keep your fingers wet when working with caulk because it keeps it smooth and easier to work with.


Then, smooth out those lines with your wet finger.  (There are caulking tools to smooth out those lines…..but I prefer my finger.)  Then re-wet your finger, and repeat.  After every swipe, I wipe my fingers on the wet paper towels and continue on.  If your caulk is looking bumpy……just really wet those fingers and smooth it out.  Just be quick about it all, because caulk starts drying pretty quickly.


But just to give you an idea of the magic of using caulk…….here’s the before, after adding caulk, and then after the final paint job.  See?  It’s magic!  You can’t even tell there used to be cracks anywhere!!!!


Once all your caulk is dry………paint everything!  Then your trimming will all melt into each other.

Then, sit back and let your socks be blown off.  Pretty, right? :)


Whew……only about 17 more windows to go.  We’ll just pace ourselves.  It’s so worth it! :)

Good luck!



Home Improvement: Trimming a Window (replacing the sill & apron, adding side/top molding)





Ashley Johnston

Administrator at Make It & Love It
Ashley Johnston is a professional DIY costume maker, sewist, crafter, and owner of Make It & Love It. She is a mom of 5 and a wife to a very patient (with the craft clutter) husband. In case you’re wondering, she always chooses crafting/sewing/designing over mopping/dusting/wiping base boards……but bathrooms/laundry/full bellies are always attended to. Whew!

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Hi, I'm Ashley

Hi, I’m Ashley—the DIY-enthusiast behind this crazy blog!

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