Building a Greenhouse with Old Windows: What are the Issues?

I’m planning to build a small greenhouse with old windows. Is there anything I should be aware of? Do I need double glazed windows?

 John M. — San Jose, California

Safety is the main issue. If you build a greenhouse with old windows, never use them for the roof. A window can break if something falls on it, or from snow loading or wind shear or, in your area, because of an earthquake. Falling glass can be very dangerous, possibly blinding or even killing someone.

The same is true for glass doors. Make sure that any door and, ideally, any window that operates by swinging upward, has safety glass which will shatter into small, blunt pieces on impact, not into sharp wedges that can cut you. (Home safety glass is similar to windshield glass.) Use Lexan, windows with safety glass or code-approved skylights for the roof.

Also, building a greenhouse with old windows can be a lot of work. It’s often hard to find enough old windows of similar size and style to build with, and many old windows need to be scraped down and puttied and repainted.

Your windows do not have to be double-glazed. Double glazing gives you about three times as much resistance to heat loss (R-value) as single glazing. But that’s still not enough to make a significant difference in performance in most climates, because single-glazed windows have almost no resistance to heat loss. (Also, older, discarded double-glazed windows have often have broken seals which allow the insulating gas between the panes of glass to escape.)

To keep a greenhouse with single or double-glazed windows heated (which is probably not necessary in your climate), you would need to throw an insulated blanket over it at night and/or use a lot of energy running a space heater. Single glazed windows will work fine  for a small garden greenhouse.

Building a greenhouse with old windows can be very rewarding. For one thing, it will save you quite a bit of money, if you have the time and patience to fix up the windows. Done well, it will give you a charming result that you can’t duplicate with shiny new windows. And of course you’ll be reusing material, which is good for you and the planet.


Relevant Reading:

Buy books and help Ecotecture! If you liked this article and want to learn more, we invite you to buy books through the links below — we earn a small commission on each purchase you make, without raising your cost one cent. We’ll use that commission to expand our efforts to empower you to solve environmental problems.

How to Build Your Own Greenhouse, Roger Marshall
Building Your Own Greenhouse, Mark Freeman
The Complete Guide to Building Your Own Greenhouse, Craig Baird



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