This makeovers walkthrough stays in the order the work happens.
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 strong result.
If you like this post you might also like Other Ways to Use Old Windows, Inspiring Window Seat options, and Great Window Covering options.
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 direct 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 straightforward 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.
Handmade 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 memorable 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 low-cost. 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 low-cost. 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 well fitted 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 straightforward cleaning and energy efficiency. These Handmade 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 Handmade 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 clearly low-cost (and straightforward) 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 modest-cost-friendly and straightforward 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 strong! 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 striking 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.
Bekob, go visit Jill over at The Rozy Home — she always has great projects, like her entry closet redo, and tips, like this worth keeping 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
