Buildings like this one have become a common sight in Ukraine these days. Amidst the invasion, shells and bullets randomly shatter windows. Near the bottom of the photo you can see a window that's been patched with plywood.

Plywood keeps the elements out—as well as light. It's also a relatively pricey material. Thus British engineer (and PhD. candidate at Cambridge) Harry Blakiston Houston designed a low-cost, easy-to-build temporary window replacement that both admits light and offers some insulation.

Perhaps these should be called 15-15 windows: They can be built in 15 minutes, and the raw materials for a one-square-meter window cost $15. There are just four materials required: Polyethylene sheet (150-200 microns), PVC piping (20-20 mm), pipe insulation (10mm thickness) and duct tape.

Unlike with plywood, no circular saw (and power source) is required; a hacksaw and a pair of scissors will do.

Houston formed a volunteer organization, Insulate Ukraine, to build the windows and disseminate the design, so anyone can make them.

"Insulate Ukraine windows are triple-glazed polyethene windows designed to protect against the cold. IU windows insulate like double glazing, let light through, cost $15 per square meter of the window, and can be built at home in 15 minutes from basic materials."

Thus far Insulate Ukraine has installed hundreds of windows across the country, making an immediate difference in the lives of residents. "There was an old woman in Mykolaiv, in southern Ukraine, who had been sleeping in her bathtub for two months because it was the warmest place in her house," Houston told the BBC. "We were able to get her back to some kind of normality after the windows went in. The house was immediately warmer and lighter - she was able to rearrange everything and actually live in her home again."

If you'd like to donate, volunteer or simply spread word of Insulate Ukraine's mission, you can learn more here.