How much gap should I leave with a DIY security window bar?
How much gap should I leave in my window when I am installing a DIY security window bar?
This question might sound like a super niche topic— but it’s one of the most common ones we get from people installing window bars for the first time.
The short answer?
It depends on how much of a gap you’re okay with leaving on either side of your window bars, and often directly answers another FAQ "How Many Window Bars Do I Need?"
Sounds like common sense, right? But let’s break it down together.
Index
- General Rule of Thumb and Window Bar Types
- Case Studies
- Visual Tips and Safety Advice
1. General Rule of Thumb and Window Bar Types
Quick Tip: Match the Gaps
As a general rule, we recommend keeping the side gaps about the same or smaller than the gap between the bars themselves.
Every window bar type has a different width and bar spacing — here’s a quick guide:
- Gap between bars: 120mm
- Number of bars: 3
- Adjustable Height range: 485mm – 900mm
- Fixed Width: 340mm
- Gap between bars: 120mm
- Number of bars: 3
- Adjustable Height range: 900mm – 1650mm
- Fixed Width: 340mm
- Gap between bars: 100mm
- Number of bars: 3
- Adjustable Height range: 630mm – 1100mm
- Fixed Width: 300mm
- Gap between bars: 100mm
- Number of bars: 4
- Adjustable Height range: 630mm – 1100mm
- Fixed Width: 420mm
- Gap between bars: 100mm
- Number of bars: 5
- Adjustable Height range: 630mm – 1100mm
- Fixed Width: 540mm
2. Case Studies
Let’s try an example. Say your window is 1000mm wide by 1000mm high and you're thinking of using one bar in the middle. Here’s how much space would be left on each side:
| Type | Bar Width | Gap Between Bars (Inside) | Remaining Gap (Total) | Side Gap (Left and Right) |
|---|---|---|---|---|
| A | 340mm | 120mm | 660mm | 330mm |
| B | 340mm | 120mm | 660mm | 330mm |
| C | 300mm | 100mm | 700mm | 350mm |
| D | 420mm | 100mm | 580mm | 290mm |
| E | 540mm | 100mm | 460mm | 230mm |
Installing 2 Window Bars on a 1000mm Wide Window
| Type | Width per Unit | Total Unit Width (x2) | Gap Between Bars (Inside Unit) | Remaining Gap | Gap per Section (Left / Middle / Right) |
|---|---|---|---|---|---|
| A | 340mm | 680mm | 120mm | 320mm | 106mm each |
| B | 340mm | 680mm | 120mm | 320mm | 106mm each |
| C | 300mm | 600mm | 100mm | 400mm | 133mm each |
| D | 420mm | 840mm | 100mm | 160mm | 153mm each |
| E | 540mm | 1080mm | ~100mm | -80mm (overlap) | N/A (bars overlap) |
📌 Explanation on the Gap per Section (Left / Middle / Right):
Since We're installing 2 units side-by-side across a 1000mm wide window, after subtracting the total bar width from 1000mm, we get the remaining open space.
- That space is then split into three:
- The left gap,
- The middle gap (between the two units),
- The right gap.
Example — Type B:
- Two Type B bars: 340mm x 2 = 680mm total width.
- 1000mm - 680mm = 320mm left over.
- 320mm ÷ 3 ≈ 106 mm per gap. (it is safer to round down)
👉 ~106mm gap on the left,
👉 ~106mm gap between the two bars,
👉 ~106mm gap on the right.
You can reach the same conclusion with Type A, but it only extends up to 900 mm on one side, which isn't enough to cover either the 1000 mm height or width of the window.
One more tip on choosing a security window bar:
When comparing options with similar remaining gaps, we recommend choosing the window bar that covers your space with less extension.
A less-extended window bar has greater structural integrity and offers better long-term durability.
In general, the more a bar is extended, the less robust it becomes. If possible, go for the option that fits your window more naturally, especially if security is your top priority.
3. Visual Tips and Safety Advice
- Looks vs. Safety – Some people don’t mind bigger gaps for the look. Others want them as small as possible for security.
- Start Small – If you're new to DIY, we suggest ordering fewer window bars* at first. You can always add more later (they’re removable from the inside — but not easy to remove from outside, so no stress).
- Avoid Returns – It’s easier to order extras later than to go through the hassle of returning bars you don’t need.
*By the way, those expandable Window Bars are also known as expandable Window Security Bars, Burglar Guards, Security Window Grates, and Burglar Guards.
Still Not Sure?
No problem — we’re happy to help!
Just send us your window measurements and, if possible, a photo or two of what you're working with.
If our DIY range doesn’t cover it, we can also point you to our partner, Xpanda Security, who specialises in custom-made security options.
Thanks again and stay safe!
