Monday, May 25, 2015

Basement Window Replacement

We set out on the task to replace the old broken and rotten basement windows. Originally we had considered replacement hopper style windows that open allowing air flow. However, the dimensions of the window openings mandated that we would need to order a custom size window as opposed to using a standard size $70 version from the local home store. Custom hopper windows, it turns out, cost a lot more in a non-standard size. A local company had quoted us $350 each to replace our current windows with new hopper style vinyl windows. A much less expensive option was to go with glass block. We compromised and ordered our glass block windows with a vent that would allow air flow.

Over the years the glass window panes had broken for various reasons. In one instance a lightning strike close to the house had shattered one sending shards into the basement.

This window was fitted with a dryer exhaust tube to facilitate laundry in the basement during major house construction. The insulation to either side was to plug panes where the glass had broken.

 Patches cut from scrap materials had been somewhat effective in keeping the elements out.

Only two of the four windows seemed to have retained their glass over the years. There were many other issues with moisture and drafts seeping in around all of them.

For some reason there was an electrical outlet wired outside one of the windows. I'm told this was used as a convenient power supply for outdoor equipment. I bet the local inspector would love this. It must come out as part of this job.

Each window had a mesh screen in front of it. I'm not sure what this material is but it became quite brittle and useless over the years.

The old window may have tipped out or been removable at some point, but it was screwed shut and had been painted over a few times by now. It was stuck in the frame quite well and needed a bit of coaxing to get it out in one piece, avoiding more shattered glass.

Prying around it and lightly tapping from the outside allowed us to pop out the windows in one piece.  The next task was to cut out the frame.

 A sawzall was used to make a cut in the bottom of the frame creating a good spot to pry it up.

 Next, each side was pried away from the stone foundation.

The old stone mortar was in poor condition and simply brushed off the rocks. These areas will need to be repaired  as part of the process. Much of the old mortar on the bottom sill was powdered as well and had to be chipped and vacuumed off.

The top frame was cut in a similar fashion to the bottom and came out as the sides were bent inward.


The bottom of the frame was very close to becoming dirt. They had been so damaged by moisture that there were plant root systems growing in them.

The sides were re-mortared and later tooled flat. One window had a cavernous gap on both sides where the mortar was gone; it took about 40 pounds of mortar to plug some gaps and bring the sides back where they needed to be.

Next the new window was shimmed into place tight against the wood beam above. Mortar was added under and around the window and allowed to cure for an hour or so.

A shim screwed to the top beam helped prevent the window from falling inward while it was being positioned.

After the mortar cured enough to support the weight of the windows the shims were removed and the gaps they left were filled with more mortar.

An angled shelf was tooled into place once the shims were out, this should help water shed away from the foundation. Any time we added or manipulated the mortar we kept a sponge handy to wipe up any mortar film that had got on the window.

Inside, the mortar was brushed and blended using a whisk broom to match the finish of the surrounding walls.


This process was repeated 3 more times and we had our 4 windows done.

Here's the final product. We'll wait 30+ days for the mortar to cure to a low moisture content then paint the inside white like the rest of the wall.

Hopefully these windows will withstand the elements better than the previous ones. We might also build wood framed screens to go in front of these to hide the block and simulate the look of the older windows.


  1. What a great replacement for a basement window. I think that the thick glass can be an amazing addition to anyone's basement windows. Something that really is interesting as well is that you showed how you removed the old window and sealed in the new one. Hopefully it will be able to last you years.

  2. Nice post. Thank you for sharing this information.
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  3. It is about time I learn so much about doing some lagging changes that I have been ‘singing’ about for months now. I thought basement windows are a simple thing to fix until I came across this post. I guess I am now more prepared to do what is expected of me unlike the general thoughts, which have made me think it will cost me way below $200.

    Doug Lowe @ M & M Glass

    1. We used Pittsburg corning premade glass block windows from home depot. You can order them in various sizes to met your needs. They worked well and were not too expensive. Yep, sometime you just need to start the job and get down and dirty. Good luck.

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    1. We used Pittsburg corning premade glass block windows from home depot. They worked out great as you can order them in various sizes. They have been durable and were easy to work with.

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