Historic windows present challenges when it comes to mitigating the effects of UV and thermal transfer. Providing both UV and thermal barriers for historic windows is often accomplished via some ancillary attachment. Here are a few examples, with associated pros and cons:

 

Insulated roller shades
- Can protect against UV while still allowing natural ventilation

- Can sometimes be concealed when not drawn (doesn't always interfere with historic import)
- Not the best possbile air or thermal barrier - e.g., in winter, can still allow for condensation to form on glass

 

Sealed quilt or roman shade

- This refers to a heavier, well insulated interior shade mounted on tracks that forms a reasonably good air seal around the window
- A well known brand is  Window Quilt (claimed R value from 4.6 to 7.1)

- Bulky, and may not appeal to some; may detract from historic import
- Better air/termal barrier than a roller shad, but might be less than adequate if both UV protection and natural ventilation are desired in summer

 

Exterior storm window
- Might help to further mitigate any air/moisture infiltration issues
- Newer ones are designed to be nearly invisible - don't detract from historic import
- Can be onerous to remove every spring and replace every fall

 

Use of exterior awnings, overhangs, or plantings (transpiration, shade)
- Natural, passive
- Can help extend the effects of existing heating/cooling mechanisms

 

In general, what approaches have any of you attempted, and what sort of results have you achieved? What seems to be a preferred strategy (or combination of strategies), or potential best practice solution to this problem?

Tags: Barrier, Preservation, Thermal, Transfer, UV, Windows

Views: 1791

Replies to This Discussion

I like using storm windows & solar screens - in some cases I will also recommend a low-e film being applied

Good Energy Circle article on basic use of landscaping to facilate/improve cooling

I've found insulated (foam-backed) roller shades to be a simple solution for blocking UV and heat during the summer. The trick is to get as close a fit as possible between the shade and the sashes (or sash stops) and to have the roller positioned horizontally so that the panes are completely covered. This usually means an inside mount, and sometimes a bit of fussing, especially if the window frame is not completely square. For example:

The nice thing about an inside mount is that it keeps the roller out of the way of more decorative (e.g., historic or period-specific) window treatments. Furthermore, the shade is easily concealed when not in use. For example, here is the same window with the roller shade down, blocking the sun during the early part of the day:

And here it is later, rolled up after the sun had transited above the overhang. Note that the shade, and even its control cord (secured at its lower end to the casing, for child safety), are almost fully concealed by the period fishtail swag:

Here's an example of a period linen festoon that obviously could also easily conceal a roller shade (even though there's no roller shade installed in this photo):

A disadvantage of roller shades is that you can't really get a positive seal between the back of the shade and the sash or stops. Such a seal is needed when the shade is pulled down in the winter to prevent the warm air of the room from hitting the cold surfaces of the panes and condensing. And for any walls that lean inward (as you'll often find in very old homes), there may be a considerable separation between the back of the shade and sashes/stops, as the lowered shade will lean away from the wall, making the shade less than effective in either winter or summer.

In these situations, what might work better (although I have yet to try these) are insulated Roman shades, or a commercial product known as a <a href="http://www.1windowquilts.com/">Window Quilt<a>, that attaches to the window casing via a track. The Window Quilt product is heavily insulated, and the manufacturer claims both air blocking and high insulating properties, ranging from about R-5 to R-7, depending on the number of panes and glazing.

By contrast, I have not been able to find any published R values for the foam backed roller shades. However, I intend to also install the Window Quilt in one of my "test windows", and will attempt to do some thermographic analyses of both solutions (and maybe a few others, as well), so I can come up with an empirical basis for comparing these different approaches.

So stay tuned for more.... :-)

Why no mention of interior storm windows?  They seem to be better than exterior units in many respects.  I have no hands on experience, but the info available on the web seems to make a compelling case.   Anybody with first-hand experience?

Hi Alexander,

I personally have no first hand experience with them. I'd never meant to exclude them from my laundry list above; just wasn't thinking about them at the time. I agree with you that the information available is quite compelling -- they would seem to address air exfiltration and condensation issues, and they don't interfere with the external appearance of historic windows. They're also easier to handle. On the other hand, they wouldn't protect the exterior surfaces of an historic window the way an exterior storm window would.

But in any case, thanks very much for joining the group and for your comment. Consider interior storms to be added to the research topic list.

~ John

I've been making and using interior air panels for 15+ years. They are low cost and effective.

More details here:

http://historichomeworks.com/forum/viewtopic.php?t=193

This is the only professional interior storm window I have found.

http://www.indowwindows.com/

We have not used them on any projects yet.

Thanks Steve. I'm accumulating a list of links to manufacturers, so will include this one. Appreciate it!

Old House Journal article on "How to Save Energy with Awnings" (August-September 2011):

http://www.oldhouseonline.com/how-to-save-energy-with-awnings/

John, I worked on home in historic Maysville, KY several yrs. age. The home was limestone ext. w. framed walls int.. The original windows had been well maintained casement units. The air leakage was significant and replacement was not an option. After through ext. and interior caulking around the perimeter we used Magnatite interior windows. The installation was fairly easy other than taking percaution not to scratch the acrylic glazing. Cutting the corners of the magnetic seals requires careful layout so there is no air leakage around the edges. My main concern is the adhesive holding the metal strips that the magnets attach to will hold up in the long run. As far as doing the job of sealing the windows they work well.
Hi Ed, thanks very much for your testimonial on interior storms. Good to hear about others' experiences with these. And thanks for joining the group!

I have exterior storms made by Allied window. I mount them to furring strips that I have installed inside the windows casing. That way, the trim is not obscured, so they look like an original window. They can be ordered with whatever glass you like and come in several standard and any custom color. They cost about 1/2 as much as replacements and retain the beauty of those old fashioned wood framed windows, while performance is on par with any double pane.

I like exterior storms better than interior, because I don't like to remove and store them for the summer and they are just as important in summer as in winter even here in zone 6. Also, I don't like covering the often painstakingly restored wooden windows, especially with plastic.

For my own house, I use insulated roller shades, also inside mounted so as to be inconspicuous when not in use.

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