RetireJapan

grimpeur wrote: ↑Fri Nov 12, 2021 2:38 am Another way to do this as DIY is with PVC frames sold by a company called Hikari. Some home centers, Cainz Home at least, stock the kits. The link is just one example. The kit does not include glazing, just the runners that fit in the window and the framing to go around the glazing sheet. For Google searches try "DIY 内窓"

https://www.cyber-reps.com/easywindow/Kit1.html

They suggest you do it with rigid polycarbonate, ribbed 4 or 4.5mm sheets with an air gap, that are mostly transparent except for the ribs. However, depending on the size and how much of the 1820 by 910 home center sheet you waste, it may actually be cheaper to get custom made 4mm acrylic sheets that are solid and almost perfectly transparent. ...

I looked at the link, and tho it may be available as a custom order, in the link the max width is 1.8 meters. Each of ours is about 2.6 meters wide.

I've seen some ribbed plastic at the home center, never thought about using that, may have another look sometime. But again, with my process above, I can use a single sheet (trimming where needed) with no "joins" to deal with.

Custom acrylic sheets, given that 1.8 tall and 2.6 wide is possible, would be great.

For a big width, I guess you'd have to line up the rails best you can end-to-end and alternate sashes in the front and rear slots to cover the entire window.

For full-height polycarbonate, one of the manufacturers recommends using aluminum reinforcement over the clip-on frames to stop the glazing from bending. From the stuff I've seen, the 4.5mm sheeting is much more rigid than 4mm. Its about 4000 yen a sheet, so 5m wide would be 20,000 yen, so yeah, starting to get expensive. Is the film you're using the polytunnel stuff? People grow melons in Hokkaido over winter in (heated) polytunnels, so film is much more effective that some people may assume.

Our place was built in 2007, so we have double glazing which is aluminum outside and PVC inside. It's not too bad, but not great either. We're in the mountains and get cold winters with an average temperature that is subzero for about three months. We have a mix of curtains and shoji as coverings. I'm going to make openable uchimado windows using the kits I linked to, but only in our toilets where the humidity is high and we get condensation on the coldest days in midwinter. I'll probably buy custom size acrylic, which is about 4500 yen for a 90x60 window (two 90x30 sheets for an openable window). I'll do our bathroom changing room too, the room that needs to be the warmest, but it has narrow vertical slit windows and I'll just press in single sheets that will not open. I don't know how it will affect room temp on the whole, but I expect the windows themselves to be 5C warmer. Our frames have thermal breaks between the aluminum and PVC sides, but the bottom parts of the frame still get 5-6C colder than the glazing itself.
https://acrylic-online.com/

I've got another room where I want an inner window, but it will be with black polycarbonate to black the room out for a projector. It's a washitsu with shoji I can hide the inner window behind. Once the rails go in, I might consider making clear windows for winter, I'll have to see.