How to Add a Glass Window to a Hollow Core Door

Few of us live in homes with solid wood doors. Hollow core doors do the job on a budget, but they aren’t always, er, beautiful. We’ve shared some ways to update doors before, but today Beck is back (remember her furniture refinishing tutorial?) to share a how-to that will make your hollow core doors look like so much more! Give Beck a big welcome back and learn how to add glass to a hollow core door:

How to Add a Window to a Hollow Core Door
by Beck from Beckwith’s Treasures

Hi, I am Beck from Beckwith’s Treasures. I am excited to share a simple tutorial for dressing up a boring interior, hollow core door!

I wanted to add a window to my laundry room door. It is a small room and while I am RARELY in there with the door shut, I thought it might open up this hallway a bit.

You will need the following supplies

(the lengths for the wood will depend on the size of the opening)

One interior, hollow core door! To remove the door just remove the 3 hinge pins. (slip them back in the hinges on the frame so you don’t loose them…trust me!) I use a tiny screwdriver and hammer to remove the hinge pins. If yours are really stubborn, try spritzing them with WD40 first, then remove the pins!

A glass insert (measure AFTER you have framed out the opening. I subtracted 1/8” from the actual opening to give me a tiny bit of wiggle room)

Your board material will depend on your opening…if you have a 22×36” opening you will want to buy at least 12’ of each

• ¾” board material for bracing (1×4 or any similar material) cut to the width between the door skins.
• ¼” x 2 poplar “craft board”(will actually measure ¼” x 1 ½”)
• ¼” x 2 door stop trim (Again, will actually measure ¼” x 1 ½”)
• Small trim…you should be able to find a ¼” x ¼” trim at your home improvement store.

plus

• Wood glue
• Silicone caulk
• ¾” Trim nails

Tools you will need:

• Skill saw
• Jig saw (or hand saw)
• Trim nailer
• Caulk gun

My interior doors are typical “builder grade” six-panel, hollow core doors. When you cut into them you will find they are exactly what they say they are…hollow. Truth is, the only real wood bracing is around the edges and where the hardware attaches.

I cut out the top four “raised panels” on the door. This cut doesn’t have to be “exact” but try to keep it fairly “square.”  I used my skill saw to cut the straight runs and then a jig saw to cut out the corners. You can also use a hand saw on the corners if you don’t have a jig saw.

After I cut the hole in the door, I added bracing between the “skins.”MOST hollow core doors will measure 1 1/8” between the skins, but measure the INSIDE between the skins…that will give you the width of your bracing.

If you are familiar with wood cuts, you know that 1 1/8” is not a standard cut. You can probably go to your local door shop and asked for some wood strips to use for bracing around the cutout but I decided to use some wood I had on hand and rip it down to the width I needed.

I do not have a table saw, so in order to make perfect straight cuts with my skill saw I use a metal yard stick as a guide.

I drilled little holes in a large metal yardstick. I measure for my cut and mark the line on the board, then I secure the yard stick with screws 1 1/2″ from the cut line…this basically creates a “guide” to run my skill saw along and allows me to cut a straight line.

After cutting 1 1/8″ bracing strips, I cut four pieces the length I needed for the four sides of the opening. I applied wood glue and slipped the strips between the door “skins.” A little trick…set a screw on each end of the bracing before putting it in the door…that way if it slips too far into the door, you can use the screws as “handles” to make adjustments. Then just back the screw out when you have finished clamping.

I measured from the inside edge of my bracing strips to the outside edge of the door…all the way around….and adjusted each so that I had the same distance from edge to edge.  My cutout was NOT the exact distance from the edges, but the strips need to be since I would be attaching my “frame” to it. I also measured the opening to make sure it was the same width and height all the way around.

After making adjustments to each strip and making sure each was in the proper position, I clamped them and let the glue dry.

No need for nails…wood glue will do the trick if you let it dry well!

After the glue dried, it was time to add the “inside” framing. Fortunately the width of the bracing and the skins combined was 1 1/2″. That worked out perfectly for 1/4″ x 2 (really 1 1/2″) craft board (available at Lowe’s) as my frame!

I measured and cut them with my chop saw. I pre-primed my trim pieces with Kilz and sanded and then I installed them with glue and trim nails.

Yes, I noticed the bottom frame piece was a tad off…my bad. I ended up “lifting” it, removing the nails and repositioning it so it was flush with the side piece!!! One of the many stupid frustrations of DIYing…the dreaded “oops.”

I wanted a very simple and small trim since the real focal point of the entire project is the window! I thought I could use the 1/4″ x 2 craft boards but they only came in 3′ lengths and the height of the window was over 36″. I ended up buying “door stop” material….the piece of trim on the inside jamb of a door that actually stops the door. It is 1 1/2″ wide and 1/4″ thick and it comes with or without a decorative profile on one edge. I ended buying the one with a little decorative edge, just for a tiny bit of detailing! I trimmed both sides of the opening using glue and trim nails. (Forgot to take a picture after the trim was placed, but you can see it in the next picture!)

I found a teeny tiny little decorative trim to use as a “frame” for the window insert. It’s really tiny…1/4 wide. Since my frame is 1 1/2 wide, I marked the center (3/4″) and then 1/8″ on each side since glass inserts are usually 3/8 to 1/4″ thick.

I cut and CAREFULLY glued and tacked the tiny trim on the line on one side only.

At this point, I went ahead and caulked everything, puttied the holes, gave it a light sanding and painted it all. I did this so I would only have to tape off and paint one side of the window trim after the window was set in place! (Mistake alert! I didn’t prepaint the backside of the tiny trim I put on last…so you can see the white primer through the window now that it is installed! Paint the backside of your trim before you put it on!)

This is the time to measure for your insert….AFTER the frame is all constructed. Again, I had my glass cut 1/8” smaller than the opening, just to give myself some wiggle room, but not so much that the small trim wouldn’t cover it. It is important that you get the dimension right, especially if you are ordering tempered glass since it can not be recut after it is tempered!

(I had to wait a week because I didn’t think about the fact that they might just have to order the glass I wanted…which took “3-5 business days.” Then I had to wait ANOTHER “3-5 business days” because they ordered the glass wrong…delays are inevitable! Also, the glass I feel in love with ended up being about 3x what my “guestimate” was! I would suggest getting a “rough estimate” for both time and cost before you hack a hole in your door!)

After the paint dried (and the glass FINALLY came in!) I applied a SMALL bead of clear silicone caulk all the way around the inside of the tiny trim and set the window in place (It is best to do this with the door laying flat!) The silicone is important because it holds the glass in place and creates a “soft bed” for the glass so it won’t rattle around in the frame.  (Don’t go crazy…pure silicone is not paintable and you do not want it oozing out onto the trim. If it does, let it dry, then trim it with a utility knife and then wipe it down with mineral spirits!)

After setting the insert into the frame, I glued and tacked the tiny trim on the other side of the window. (Do this VERY carefully…if you hit the glass with a nail it WILL shatter!)

TA DA!!!! I absolutely LOVE it. The glass (reeded glass…google it!) is absolutely perfect.

If you are installing glass in a door, I would strongly recommend getting a piece that is  ¼” to 3/8”thick and “tempered.” Tempered glass is about 4x stronger than “plain” glass and if shattered, it breaks into a bunch of tiny, relatively harmless pieces vs. the super sharp shards of regular glass!

Tempered glass really isn’t that much more expensive…especially when you consider the safety factor!

Also, the glass will be much heavier than the “hollow” door…so this is the time to replace the short hinge screws with longer screws that actually go into the framing of the door. You can buy longer hinge screws, but I just used black sheetrock screws. I will probably change them out next time I make a run to Lowe’s. This is important because the weight can cause the door to “drag” or stick on the knob side. For that matter, if you have a door that drags or sticks, try replacing a few of the short hinge screws with longer 2-3”screws! Replace one screw at a time and start with the hinge that is across from where the door is sticking…example, if it is sticking at the bottom, try replacing the screws in the bottom hinge. This door was sticking even before the new glass and using the longer screws worked like a charm! (In the picture above you can actually see where the black paint on the door rubbed off on the door jamb!)

If the holes were the screws go are stripped out, try this little trick.

There you have it. A tutorial for dressing up an otherwise boring interior door! There are so many other things you could do with this same process…maybe a chalkboard insert or fabric or even a MUCH less expensive glass!

You are only limited by your imagination!

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Beck, thanks for paying us another visit and sharing your awesome tutorial!

Remodelaholics, you can see more of Beck’s laundry room here, and be sure to head over to Beckwith’s Treasures for all sorts of furniture refinishing projects (like this grandfather clock) plus Beck’s list of what you need in your toolbox!

More ways to update interior doors:

add glass to a wood door

build your own door with glass pane

turn bifold doors into french doors — method 1

or method 2

or try these ways, too:

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