What are Glass Block Windows? And What Can You Do With Them?

By thewriteDuffy •  Updated: 07/07/24 •  7 min read

You have likely seen glass block windows in some older buildings like schools, office buildings, or some homes built in the 1940’s through 1980’s. While they fell out of popularity in the last few decades, they have been gaining popularity recently for those looking to make an impact with their satisfyingly angular, Art-Deco aesthetic.

So, what are glass block windows? Just like the name suggests, glass block windows are translucent, thick blocks of glass that you stack together to make a full window. Glass block windows allow light through them but can not be opened and you aren’t able to see through them.

Quick to install and top-notch in terms of insulation and weatherproofing, glass block windows make for an interesting alternative to standard frame and pane windows.

Because you can’t see through the individual glass blocks, these make excellent, striking privacy windows. Since glass block windows are almost like masonry, they also offer greater security.

What Is the Purpose of Glass Block Windows?

Glass blocks can be used to create superbly weather-proof privacy windows in bathrooms, ground-floor bedrooms, and basements. The blocks are often also used to build room partitions and privacy screens where light is still desired on all sides.

Not a fan of frosted or obscure privacy glass? Glass blocks may suit your tastes better, especially now they’re available in a range of colors and textures. Glass blocks reflect light well, giving the illusion of space in a room. This makes them a smart choice for brightening and freshening up bijou bathrooms and gloomy basements. 

Are Block Windows Outdated?

Until recently this style of window was considered outdated. But, with new materials and structural design ideas, glass block windows are making a return and looking at home in modern homes when used well.

In modern homes, you can style glass block windows in such a way that it captures the clean lines and airy feel of a contemporary home, but it’s best to avoid frosted glass blocks and only opt for colors that complement your decor.

For a contemporary glass block look, it’s also best to avoid imposing, large glass block windows and to use muted wall tones, plants, furniture, and gentle lighting to soften the look if needed. 

How Long Does It Take to Install Glass Block Windows?

It doesn’t take long to install glass block windows. By far the quickest and easiest glass block windows to fit are the prefabricated models.  If you’ve measured the window space correctly, installing them is a breeze and smaller specs can be fitted within just an hour or two.  

The rod-and-mortar technique is the most common method for installing glass block windows. Because it involves no framing, the installation is remarkably quick.

Because you install glass block windows by laying them like bricks, the job requires a special glass block mortar and expansion material for the perimeters. This will allow for the natural expansion and shrinkage of the blocks. The mortar may take up to 24-48 hours to set and after that time, silicone can be used to seal the window.

Glass Bock Windows

Are Glass Blocks Cheap?

Glass blocks windows tend to be cheaper than similar-sized double-pane windows. At Home Depot, a box of 8 average-sized glass blocks costs around $100 depending on where you live. Prefabricated glass block windows (which are pre-mortared), with options to fit standard-sized windows, cost between $150 and $500. 

When you’re working out your glass block window budget, the type of block you go for can make a big difference to your material costs. Factory glass blocks can cost as little as $5 per block for a basic, clear glass cube. Customized blocks are more expensive but they give you the freedom to choose your thickness, color, texture, and finish – plus they tend to be shatterproof and more durable.

If you’re not keen to DIY this project, you’ll need to take the cost of installation into account, and unfortunately, you can expect to spend almost as much on installation as you did on materials – if not more!  You need to budget around $300 for the fitting of a small glass block window.

Can You Replace One Block in A Glass Block Window?

A cracked or shattered block spoils the overall look of the window and you might panic that the entire window needs to be removed to fix the problem. The great news is, most of the time you can get away with simply removing the one, damaged block.  As long as your window was installed to a high standard, the extraction process shouldn’t destabilize the structure.

This has to be one of the real plus points of a modular glass block window – they’re so quick and relatively inexpensive to repair. When you’re first installing your window, make sure you put aside a few spare blocks just in case!

The repair job simply involves chipping away the mortar from around the damaged block, sliding it out, hoovering away the debris in the hole, then replacing the block with a fresh batch of glass block mortar. Remember to do this job on a dry day, to make sure the mortar sets properly otherwise you may have issues with leaks.

Are Glass Block Windows Load-Bearing?

Glass block windows should not be load-bearing and sturdy though they are, they are not fit for this purpose. Using glass blocks to load bear doesn’t only put you at risk in terms of building regulations, but you also compromise the safety of you and your home.

It’s essential to note that glass blocks are only certified to carry their own weight, so if you’re renovating or building, do not count on these windows for structural support. Adequate support should be provided at the “head” of the window and lintels are sometimes used for this purpose. Glass block windows installed in load-bearing walls can end up cracking and shattering over time because of the weight.

Is Glass Block a Good Insulator?

Glass block windows are excellent insulators when properly installed, thanks to their thickness and tight mortar and silicone seals.  This has traditionally made them a good choice for basement windows, which are otherwise notoriously leaky and drafty!

This type of window is comparable to a double-pane thermal window when it comes to insulation and energy efficiency. When you think about the thickness of the individual glass blocks and the two layers of glass, you can see why great insulation is one of their key features. 

Not only do they have a double layer of glass, many also contain a core of pressure-controlled argon gas.  This gas reduces heat loss from inside the home to the outside. Heat loss and drafts are also greatly reduced by the mortar between the blocks and around the perimeter.

Glass block windows are available in a rainbow of colors.

Conclusion: Do You Want to Go With Glass Block Windows?

Glass block windows are growing in popularity and have a lot to offer your home.  If privacy is a priority, and you want something budget-friendly but a little bit different; this energy-efficient, unusual style may tick many of your boxes. If you’re not sure that glass block windows are right for your space, click here to see our list of the 13 most popular window styles for your home.

Glass block windows are an ideal choice for home renovations or infill homes in busy cities thanks to their added privacy and security.


At home, April is a mom, wife, and DIY darling. Among other home projects, she helped her husband Dan renovate their 1986 bungalow and is currently designing and decorating the 2023 custom home they are building themselves. Professionally, April is a writer, author, and online marketer with 15 years of experience writing for newspapers and magazines, building online authority websites, and publishing books.