Step by Step Interior Window Trim

Interior Window Trim Work

The interior of the house is now coming together.  It always strikes me as funny that a bit of trim work can really make a house’s look (even unpainted) start to pop.  I have spent the past week cleaning out the excess foam insulation that surrounds the windows, picking out any staples and nails, and generally just cleaning up the exposed frames around the windows in preparation for the interior window trim work.

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There are loads of methods to trim out a window and most require a fair degree of carpentry experience to make them look just right. I started by watching the training videos and course materials in the Tiny Home Builders Online Workshop.   I’m going for a fairly basic window frame.  Partly because I know the limits of my carpentry skills but more so because I don’t want to take the time to work on fine details that my wife and I won’t ever care about.  We’ve lived in lots of old houses that use this basic technique and if its good enough for old houses…its good enough for us.  The only downside of this technique is that you end up with a narrow sill.  So you wouldn’t want to use this technique if you plan to sit things like plants and such on your window sill. For us though…in a tiny house, every inch matters.

Since I’m on a budget I opted to use fence grade planks cut down to size.  Its an inexpensive cut of wood that when sanded and painted will look just as good as an expensive piece of wood.  The first step (after cleaning) is measuring the depth of the interior trim you’ll be building (video shows this part).  You’ll measure from the window to the outer edge of your wall.  The goal is for the interior trim to be flush with your wall when finished. I suggest measuring each corner since its possible that your window could be askew and you might have a slightly different depth in one part of your window. If this ends up being the case you wouldn’t cut with the table saw, but instead with a circular saw to get the angle correct. As for the width measurement….that’s just the width from frame to frame member.

You are now ready to cut your bottom interior trim piece. I’d suggest nailing it in place since you’ll be measuring from it in the next step. Now you’ll measure the vertical interior trim pieces.  The depth measurement is the same as above.  The length of the board is measured from the top of the bottom interior trim piece you nailed in to the top of the interior window frame (see picture 2 below).  Now you’ll nail in the side pieces. Measuring the depth of the top interior trim piece is the same as listed above.  For the width its just a matter of measuring from one vertical trim piece to the other. Slide it in and nail it in place. You could use trim nails or staples (I used trim staples) and then you are ready for the next step, the front trim pieces. Below is an example of one window’s interior trim being built out:

The front trim pieces width can be whatever material size you’ve chosen to reduce the amount of table saw time you are spending. I opted for 4″ boards which in reality are 3.5″ in width.  I started with the bottom piece by measuring the length of the interior finished window from the interior of one side trim piece to the other side.  Then I added 7 inches.  I did this because the material is 3.5″ thick and I’ll have 1 vertical board going up each side….3.5 x 2 = 7. Cut the board and then make a pen/pencil mark 3.5″ from each side.  Line those marks up with your interior trim pieces and be sure the top of your face trim piece is flush with your interior trim piece.  Then nail it into place.

The vertical face trim pieces are measured from the top of the bottom board to the bottom of the interior trim piece.  Cut two of those and nail them into place on top of the bottom face trim piece. For the top face trim piece….DO NOT repeat the step bottom piece step.  Its likely you’ll have come out of square a bit and/or your trim work isn’t 100% on point.  To make it look like its all lined up, just take a measuring tape and measure from the end of one vertical face trim piece to the end of the other.  Then cut your board that length.  Nail it up and viola, you are done with a window.

To finish up the trim work you’ll need to fill in your nail holes the gaps between the interior and face trim, and face trim to face trim gaps with caulk or wood putty.  I opted for wood putty since I still had to sand everything down. If you use a caulk you’ll want something that is paintable and sandable (if you haven’t sanded yet). The below video and pictures of another window I did in order should highlight a bit better the process.




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