How to Build and Install Custom Window Mullions (Grids)
Learn how to transform your windows with custom window mullions (grids) through this step-by-step guide, complete with helpful tips and tricks for a stunning result.
If you like this post you might also like Other Ways to Use Old Windows, Inspiring Window Seat Ideas, and Great Window Covering Ideas.
How to Build and Install Custom Window Mullions
Updating a cookie cutter house to a custom stylish home usually means combining large projects (like entry renovations and updating cabinets) with smaller details like choosing the right paint color and window treatments.
Jill has put a lot of work into her home (remember her range hood and trimmed arched windows?) , and this latest project is simple but has such impact on the room! Half of the windows in her home had grids (mullions) — but the other half did not. So Jill came up with a great way to make her own window mullions, inexpensively, so that every window has the same grid look! This easy project really improves the aesthetics of her home, so the large windows match the paned windows, and these new grids fit right in the existing window frames.
DIY Window Mullion Grids, Step by Step
by Jill from The Rozy Home
Hi everyone! It’s Jill from The Rozy Home. I have worked for almost 5 years (yes, 5 long years) to make our house our forever home. My most recent project is one of my favorites to date. You see, I’ve got an AMAZING view. It is just spectacular – during the day. But at night, when the view disappears, I’m left with two huge, boring windows in my dining room. I haven’t been 100% happy with the windows in my dining room for a while now, but I never knew what it was.
And then I had my ah ha moment. I realized that what bothered me is that every window on the front of the house (including the arch windows and even the little windows) have grids but every window on the back and side did not. At first I thought the builder did this because he wanted to enjoy the view. The more I thought about it, though, the more I realized he did it to be cheap. I think that if he really wanted to enjoy the view, he would have picked larger windows without huge pane dividers going through them.
With this in mind I decided to add my own window grids. I will be honest with you – I didn’t know where to start. Naturally I took to the internet and was so disappointed by what I found. I found tutorials that either were too complicated or looked really, really cheap. So I did what I normally do with projects – drank coffee and just thought on it.
I walked around the house and looked at the windows with grids. Then I realized the grids were simply made up on two vertical pieces and 6 horizontal pieces. With that bit of knowledge I headed to Home Depot to find the perfect trim.
Quick note: traditional mullion grids as made by manufacturers are thin strips of aluminum between the panes of glass on a a double-pane window to make for easy cleaning and energy efficiency. These DIY windowpane dividers are easily removed for cleaning the glass panes and saved me a bunch of money by making my own grilles and giving me the aesthetic appeal I wanted. Homeowners who want the true architectural style of the window muntins grids can talk to a window manufacturer to retrofit or replace their windows.
Dividing the windows into smaller panes of glass does slightly reduce the amount of natural light in the room, but this DIY doesn’t impact the structural integrity of the window, so consider your personal taste and make an informed decision about what you like for your windows.
Step 1: Choosing the Mullion Grid Material
While at HD I looked at a ton of trim. I thought about wood. The only problem is that the pieces on the front are not wood so they wouldn’t match. After a bit of searching I came up with these polystyrene vinyl screen mouldings:
Not only were they the right width, but at $2.38 for 8 feet, they were the right price. My windows are 32 inches wide and 72 inches tall and there are 4 total so decided I needed 16 pieces (which, by the way, was too much. Turns out I only needed 12 pieces).
(Update: I later traded for this pine screen moulding trim, which is just a hair thinner, so that my mullions didn’t rub on the window when I opened it.)
Step 2: Determine Mullion Grid Placement
When I got home the first thing I did was decide how wide apart I wanted the vertical dividers. I decided on two vertical pieces of wood that were spaced about 10 1/4 inches apart. Next I decided how many horizontal pieces I wanted. For that, I opted for three rows. Having figured that out, I measured the length from the top of the window to the bottom (just the glass part).
I made those cuts and attached them to the window with double sided tape. This allowed me to accurately measure the length of the horizontal pieces. After figuring that out, I went and cut 48 (yes 48!) horizontal pieces and the remaining vertical pieces.
Step 3: Paint Mullion Grid Pieces
After cutting the pieces, I took them out in the garage and spray painted the back. This wasn’t really necessary because no one will see the back of them, but I decided to “do it right.”
Here’s the thing about spray painting poly – it takes at least three coats to cover it. I used Rustoleum 2X and it still took 3 coats.
Step 4: Build Mullion Grids
After deciding how far apart I wanted each grid, I measured from the bottom of the grid up and marked the spot. I wanted mine spaced 8 1/2 inches apart, so I measured 8 1/2 inches from the bottom and marked it across the entire piece. It’s really helpful to place a horizontal stile at the bottom between the vertical stiles. This helps ensure your measurements are equal.
Next, I took out the handy dandy hot glue gun and put hot glue on the end of the horizontal stile and attached it to the vertical stile. Then I did the same thing on the other end (attaching it to the other vertical stile). It’s easier to start with the center horizontal stiles first. It will make the overall structure more stable.
Repeat the steps on the left and right sides. Allow the grids to sit for about 15 minutes.
Step 6: Attach Mullion Grids to Windows
To attach the grids to the windows, I purchased double-sided/mounting tape from Ace. I placed one piece on the back of the top of each vertical stile. On a few I attached them to the outside horizontal stiles. They stick really, really well and if they wear out they are super cheap (and easy) to replace.
So there you have it! With a little bit of time and patience, you can give your windows a more custom look.
The total cost of the project (including the paint) was $35 which breaks down to around $9 a window. Not a bad way to add some character to boring windows. 🙂
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Thank you for sharing with us, Jill! A budget-friendly and easy update!
Wow, what a difference those window mullions make! The “before” picture shows a nice room, but it feels a bit plain and ordinary. The “after” picture, on the other hand, is absolutely stunning! The mullions add so much character and charm to the space. They give the windows a more traditional look, and they really help to frame the beautiful view outside.
I’m also impressed by how much brighter the room feels with the mullions in place. They seem to let in more light, which makes the room feel more airy and spacious.
Remodelaholics, go visit Jill over at The Rozy Home — she always has great projects, like her entry closet redo, and tips, like this must-have tool for painting cabinets.
And this wraps up our holiday guest series! But never fear, we always have more great tips, inspiration,and tutorials for you.
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First published 5 Jan 2015 // Last updated 30 Sept 2024
Jill has been working for years to make her house into her forever home. With a love of high-end details, Jill works to recreate a high-end look on a DIY budget.
Lorene has been behind the scenes here at Remodelaholic for more than a decade! She believes that planning projects and actually completing them are two different hobbies, but that doesn't stop her from planning at least a dozen projects at any given time. She spends her free time creating memories with her husband and 5 kids, traveling as far as she can afford, and partaking of books in any form available.
Thank you guys for sharing! Now I’m off to do the windows in the living room! 🙂
Thanks, Jill!
Wow, that looks great, good job Jill! I have considered going to non-grid windows if we ever replace our windows but seeing both options side by side I might have to stick with grids 😀
This tutorial came at the right time, I was just thinking I need to do this to our front door and garage door! My only concern is what does the mounting tape look like front the outside of the window?
Thanks
Curious if you went ahead and tried this approach, and what the end result looked like? The only thing keeping me from attempting this is not knowing how the mounting tabs look from the outside.
Jill, Thanks for the information about building faux mullions or grids. I have a project that will require large windows. I wanted to use double panes with no grids and then add my own grids in order to save money. I ran this by my architect and he felt that depending on where the grid was attached (either inside or out) that one side would show the glue. It’s important to me that both sides look great. Why not put a grid on either side?
Any problems opening and closing the window? Is the grid installed on the outside as well?
Looks great!!
Not trying to be a stickler, or to take away from your work, but a mullion joins 2 windows, a muntin is the grids on the windows
Thanks for the info, Pat!
Actually these are muntins. Mullions join windows together.
Thanks, this is what I needed to do grids on some large mirrors; I found 3 wood framed mirrors (18″ x 66″), and will stain the wood frames and the wood trim you recommended to match to make the grids. By placing the 3 mirrors together (maybe about 2″ space in between) I think I will have a stunning “window” wall…directly across a large sunny window to really brighten and make the room look larger (a dining area). The grid look will mimic the window across from it. Hard to explain but it will look great! Thanks again!!
Beautifully done. Obviously you can add muntins to the outside, but in this case who would ever see the tape, glue, etc. If you need them then go for it. Jill does not need them. Also, an English/writing teacher told me once, if your audience understands what sentiment you are conveying, there is no need to get caught up in vocabulary. I’m fairly certain no one reading this post was confused by Jill’s choice of words for this tutorial; but, it may have been a nice bit of information for those who did not know.
I cannot TELL you how incredibly thrilled I am to have found your great bog article. We lost everything we owned in Hurricane Harvey this past Aug/Sept. and did not have flood insurance. My husband and I are retired teachers in Beaumont TX–in fact, my sweet hubby had JUST retired from 30 years of teaching, four days before Harvey struck. So, we are doing as much of the rebuilding of our little shell of a house, ourselves. I love mull ion ed windows-but the for having to replace every one of our windows–They ALL have nasty water between the panes–one neighbor actually had a small fish between her window panes. I kid you NOT!! Anyway–I actually did this exact same trick, many years ago in our first home–who can remember 38 years ago.o . But, though it did turn out well–I I ads most definitely, not as precise and savvy with it as you obviously are! Thanks to your great post, I realized I CAN do this again–but BETTER!!! And your greattips will davre us a bundle, for things like–floors, cabinets, BEDS!! Lol-Seriously!!! Thanks so very much for writing such great directionsvand having excellent pictures. I can’t wait to actually GET windows again, so I can do this!!! You’ve given thIs 58-year-old girl the guts to go for it!
Thank you so much for leaving us a comment, Marlene! We love hearing that what we share is inspiring. So sorry to hear about your Harvey damage and we wish you all the best in your rebuilding! If you want to share pictures (or ask for ideas from our other readers) you can message us over on Facebook or drop us a line here: https://www.remodelaholic.com/share-brag-post/
I cannot TELL you how incredibly thrilled I am to have found your great blog article. We lost everything we owned in Hurricane Harvey this past Aug/Sept. and did not have flood insurance. My husband and I are retired teachers in Beaumont,TX–in fact, my sweet hubby had JUST retired from 30 years of teaching, four days before Harvey struck. So, we are doing as much of the rebuilding of our little shell of a house, ourselves. I love mullioned windows-but, unfortunately, after four bids for Windows Only, the ball park figure is about $7,000–a HUGE chunk out of the 32,00 Fema graciously wrote out a check for–having to replace every one of our windows, is just a huge price point-so grids of any kind were out of the question!! They ALL have nasty water trapped between the panes–one neighbor actually had a small fish between her window panes. I kid you NOT!! Anyway–I came across your great post–a belated Christmas Miracle!!–and Bing!! A light bulb went on over my head–well, not an Actual light bulb–but you get it! I suddenly remembered–I actually did this very same project years ago, when our three kids were small!! Really!! The same trick, many years ago in our first home–However NOT nearly as well as you have done! Mine did turn out well enough–But certainly not as precise and savvy as you so obviously did!! I just wanted to say a big THANK YOU for your great post, because of it– I realized I CAN do this again–but BETTER!!! And your great tips will really save us a bundle, for things like–floors, cabinets, an entire house Lol f furniture–ESPECIALLY BEDS!! Lol-Seriously!!! Thanks so very much for writing such great directionsvand having excellent pictures. I can’t wait to actually GET windows again, so I can do this!!! You’ve given thIs 58-year-old teacher one heck of a Great lesson, and the courage to go for it!RThanks so mu
I can’t believe I found this post! Years ago I removed the muntins on our windows and lately I’ve been regretting that decision. I was just starting to look into buying new ones for the windows when I came across this post! I can totally do this…actually you’ve got my juices flowing with how I can do this a little more fancy then I originally planned.
Thanks so much for this awesome post and the inspiration!!!
We are so glad you found this helpful! Thanks for sharing your comment.
You have an amazing blog! I was looking to add grids to my windows and found a company that sells DIY kits and individual parts to create that look. All they require are scissors and a tape measure. It is super easy to install and are super affordable. You should check them out!
http://www.newpanes.com
Thank you sooo much for this post! I have glass front kitchen cabinet doors that I wanted to turn into six pane glass doors. I have seeded glass which I really love but want them to have the six pane look. I looked at purchasing mullions on Etsy for each door – for 5 doors it would have been close to $500! I’m so going to try this myself! Thank you, thank you!
You’re welcome! We’d love to see photos when you finish!