We decided window replacement to improve light and insulation was desperately needed in one of the rooms in our house.
When we purchased the property, one bedroom had a very wide window facing west. The temperature inside it in summer became unbearable as sun blazed in all afternoon. Even with curtains, the heat climbed unbearably. The window was too large for the relatively small size of the room. Plus it needed improved insulation.
We kept the door shut throughout summer days to stop the heat from spreading through the house. Sleeping in that bedroom was impossible until well after dark, giving us time to open the window and use a fan to circulate cooler air through.
So, at the beginning of last summer, our number one priority was to address the issue of window replacement to improve light and insulation in the bedroom.
We expected a change, but we had no idea that one window replacement would fix six problems!
- Window replacement gave more wall space
- Summer temperature improved
- Winter temperature improved
- Better lighting
- Window replacement identified leak
- Mould removed
Our window replacement to improve light and insulation ended up fixing six problems at once! Here’s how:
1. Window Replacement Gave More Space
Our teenage daughter had been using the bedroom with the problem window. Had she been younger, we probably would have replaced it much sooner. Younger children have earlier bedtimes. The problems of too much light and too little insulation would have been become more of a priority.
As a teenager, she was happy to wait until after dark before cooling her room and going to bed. During daylight savings time, the room was often still hot at 10pm.
Replacement of the window improved light and insulation issues. It also created a lot more space for our happy teenager. Wall space and floor space.
The large window filled an entire wall, with curtains hanging where she’d have rather stuck posters. The floor was kept clear to prevent items near the window from fading in bright sunshine if she forgot to pull the curtains before going out for the day.
Now after the window replacement, she has extra room for a desk plus whiteboard, corkboard and posters in her room.
2. Summer Temperature Improved
The replacement window is only about one third the size of the original one. Suddenly there’s less sunlight entering the room.
But more importantly, two-thirds of the wall now has effective insulation. Instead of the glass that allowed heat in, the sun is met by woollen insulation plus reflective sheeting inside the wall cavity.
The room still faces west and the relentless hot sunshine of summer, but the effects of the sun are minimal.
Home window replacement should always be accompanied by adding, replacing or upgrading insulation in the walls.

New insulation in new wall during window replacement.
3. Winter Temperature Improved
We were all amazed by the difference the replacement window made in winter. As well as remaining cool in summer, that bedroom now remains cozy in winter.
The winter temperature improved so much that the room is warm when she wakes in the morning. Internal warmth no longer escapes through a massive sheet of glass.
4. Better Lighting from New Window
In our case, the previous window let in too much light. Other homes undoubtedly need replacement windows to increase light levels, but that wasn’t our problem.
By replacing the original window with a smaller one, the room remains bright – but not uncomfortably bright. And because it is a standard window size (instead of unusually large), we could buy a venetian blind to fit it.
The venetian blind gives more control over how much light enters the room. In the past, the two choices were simply curtain open or curtain closed. Now the venetian blind can be up or down. Plus, when it is down, the slats can be either open or closed.
She only needs one curtain now. It hangs pushed to one side when not in use. Before we installed her window replacement, we had two layers of curtain – with six curtains on each layer!
5. Window Replacement Identified Leak (and Mould)
We knew there was a surface mould problem with the old window. But we didn’t know about the leak into the wall until we began the window replacement to improve light and insulation. That’s when we discovered mould in the wall cavity.
Every winter, we warmed our house and kept two layers of curtains closed near that window. We didn’t want heat to escape. But that created a pocket where cold met warm and formed condensation.
Because black mould is such a big health problem, we regularly cleaned the window and surrounds. We also kept a moisture-absorbing container between the window and the curtains during winter, in an attempt to prevent condensation.
Our window replacement required us to strip the wall away beneath the old window. That’s when we discovered the problem was much greater than we’d thought.
Rain (and perhaps condensation) had been leaking into the wall structure.
6. Mould Removed
As you can see in this photo, the wall itself contained mould. So we stripped it all out and replaced the timbers.

Mould in wall cavity, plus fluff from old insulation.
What began as a simple window replacement to fix one problem, ended up solving six problems at once.
So be prepared if you decide on window replacement to improve light and insulation. You may discover even more problems to address at the same time. We had to make a return visit to the hardware store to buy wood to replace part of the wall frame. But it was certainly worth the effort!
This was very interesting, iMom. It is so often the case when you decide to tackle one problem you find others needing to be attended to as well. Unless it is double glazed glass does let in a lot of heat so it makes sense that reducing the size of the window and adding extra insulation would greatly cool the room on the western side. It was a blessing that the leak and mould was found soi that you could rectify that problem also.
I don’t know what the difference is in price in countries where double glazing is common in windows, Pa John, but I’ve never considered the extra cost to be worth it. We have only one very small window double-glazed. Useful in a very high position where it would be inconvenient to fiddle around with a curtain. And we didn’t buy that one. It was a gift from a friend who decided not to use it.