The exterior of the first house is completed except for the windows. We’ve been exploring options, but we are compelled to use custom windows due to the design of the house.

This seems to be the result of a chain of design decisions. One of the primary design goals of this house is to make it as easy to maintain as possible. One of the ways we do this is by eliminating “hidden spaces” for water to collect or animals to make their homes. No interior spaces inside the walls; no hidden area between ceiling and roof; not even any roof insulation.

Thus, the walls are all a single layer of pine wood. The wall you see when you are inside the house is the other side of a piece of wood from the wall you see when you are outside the house. Thus, the wooden support beams couldn’t be hidden inside the walls, so they are visible on the outside. (Given a choice between smooth walls on the inside, and smooth walls on the outside, which one would you pick?)

These wooden support beams are located every 50cm, and the windows are designed to fit between this regular pattern. (Single windows are 45cm x 150cm due to the addition of the window frame, double windows are 95cm x 150cm, and the quadruple windows are 195cm x 150cm.) Aesthetically, this looks quite nice. But it means we can’t use standard windows.

So we needed  to design a window style and get a custom window maker to make them. But I don’t know what sizes of wood a window maker normally uses, and I don’t know any custom window makers nearby. So this line of thinking seemed like it would take a few exploratory trips, followed by some designing, followed by ordering the windows.

This led to my crazy alternative idea: acrylic windows. So I whipped up a design in FreeCAD to show to the construction workers so they understood what I was thinking. Here are a few screen captures:

Acrylic window with pieces separated

Another view

 
I’ve always been a big fan of acrylic. I’ve heard it sometimes called “acrylic glass”, and I’ve also heard people refer to it by its trademark names of “Plexiglass”, “Lucite”, and “Perspex”.

The properties of acrylic are quite impressive. Here are some of its pros:

• it is lighter than glass
• it has better thermal insulation properties than glass
• it may have better acoustic insulation properties compared to glass
• it is cheaper than glass
• it has a very high impact strength compared to glass
• it can be bent with a fairly simple (DIY) table top tool
• it can be cut easily
• it can be drilled through easily
• it is really easy to source here

There are really only three disadvantages of acrylic that I have read about:

• it is damaged by most chemical glass cleaners
• it scratches easier than glass
• it ignites at high temperatures

The first issue is simple: don’t use glass cleaner on acrylic. Soap and water works fine. The scratching issue is a real one, although I have read about products that can help “repair” acrylic scratches. The third issue bothered me as a possible safety hazard (what happens if a small fire causes the acrylic to ignite causing a bigger fire?). Until I looked up the combustion temperature of pine wood (the walls are all pine wood). Acrylic ignites at 460 degrees Celsius, compared to 427 degrees for pine wood. Basically, any temperature that would cause the windows to ignite would have already caused all of the walls to catch fire.

It is worth noting that many people talk about acrylic yellowing under direct sunlight. Internet research seems to suggest that this is a misconception. Some places say this is due to confusion between acrylic and polycarbonate (which is stronger than acrylic and is normally used as “bulletproof glass” but degrades under UV light). I guess I’ll find out. Unless I apply a layer of tinting to reduce the amount of sunlight that comes in and maybe add a bit of greenish color to soften the light. These tinted films claim to reflect 99% of the UV light in sunlight, so this would presumably protect the window anyway.