Old church windows

May 24, 2008 4:40 AM

Calling all Stained Glass Experts!!! Is it all right to put older stained glass pannels inside insulated glass? Older windows on church, are there better ways to protect - save energy?
posted by ok to grab bag (3 comments total)

I would contact the Preservation Services department of the National Park Service. They may know of someone in your geographical area or in this area of specialty who could assist you with this. Their brief on stained glass will give you more information on weatherproofing and the specifics around using protective glazing and screens.
posted by jeanmari at 6:43 AM on May 24, 2008

I've had quite a bit of experience as a church member dealing with stained glass window problems, though I'm not a stained-glass specialist by any means.

So, you want to install an older stained glass window inside an insulated (double-pane) glass window? Or to install insulated glass panels on the outside of existing stained glass windows?

Either way, the problem you have is this: the stained glass has dark shades that absorb sunlight and warm up as a result. Without insultaing panels on the outside, this heat dissipates in both directions and is not much of a problem. The window gets a little warm but not hot. But, with an insulating panel, the window gets hot. The combination acts just like a solar collector. I've seen windows get so hot you could not put your hand on the inside of the glass.

If these windows have been restored in recent years, the lead solder used can stand some heat. But if the solder is old, and somewhat deteriorated already, the constant daily temperature swings caused by the solar-collector effect will be problematic and will accelerate deterioration.

There are several things you can do about this. The most important is to install glass panels that have ventilating weep-holes installed at the top and bottom. Most importantly this will prevent buildup of moisture between the window and the insulating glass, which would cause rotting frames and possible corrosion to the metals. If there is sufficient ventilation it will also somewhat alleviate the heat problem, although it will also reduce the insulating effect of the panels. As noted in the NPS brief linked above, a gap of several inches is ideal.

If you have truly valuable windows, like documented Tiffany (there are a lot of "alleged" Tiffany windows out there that are not Tiffany), LaFarge, Tillinghast, etc., the state-of-the-art way to preserve them is to install a solid insulated glass windows on the outside, no weepholes, and then to re-mount the window inside that so that it's suspended in the opening with air circulation all the way around it (but in such a way that no light shows through that gap). The installation could even be hinged so the window could be swung inside to facilitate cleaning on both sides. In effect, you're hanging a picture in front of a clear window; the air circulation around all sides insures that neither moisture nor heat will build up detrimentally, and you get the full benefit of the insulated glass windows. Of course, this is the most expensive solution to the problem.
posted by beagle at 7:14 AM on May 24, 2008

i am a stained glass artist. what your talking about is called "storm glazing" and is really a MUST. if you care about the health of your windows. storm glazing is a clear glass panel on the outside [usually plate, but sometimes insulated] whoch protects the stained glass from wind, water, UV, tree branches, etc. it can be VERY expensive getting your windows fixed, so the expense of storm glazing WILL save you money eventually. i promise. make sure you have a professional do it, so it's done right.
posted by swbarrett at 7:19 AM on May 25, 2008