I tried to look for building materials second-hand. And I found an ad for these mini windows. I think they were showroom examples before, because they had handles attached to the top. This was convenient as I went to pick them up using public transport and I had to haul them back on the bus and train! They are triple-glazed, tilt-and-turn wood+metal windows. A steal for 50 francs apiece! Here's my version of window installation: 1) get it level in the opening using shims. Peel back the rubber joint and screw through the wood frame into the structure. 2) Tape around the exterior frame using weatherproofing tape. 3) Add sheathing board around the edge (for extra insulation) 4) Stuff cracks with wool (I vowed that I wouldn't use spray foam on this project...meaning I spend time stuffing wool into gaps) Now it just needs some interior and exterior cladding!