Historical Window Energy Efficiency Upgrade Standards? 

My name is David Clark, and I am an artisan/craftsman and the Old House Window Wright, out in Northern California. I'm also a long time home performance enthusiast. I have been rehabilitating and weather-stripping (WS) historic and period houses, especially 'wavy glass' windows, for 30 years.  I restore windows to the Secretary of the Interior Standards, plus a little more to better shed moisture, and then I WS them and address thermal issues. I believe I can WS a double-hung sash window to 80-90% airtightness, and single casements 100% tight, with the windows fully functional. As a home performance devotee, I state to all the preservationists I know that the best way to save historical windows is to apply Home Performance/Building Science and to WS and mitigate thermal issues.  

As preservationists and building science/home performance specialists, we are aware that the 'house is a system' of interactive interstitial parts that play off and support or detract from one another in determining the structure’s comfort, safety, durability, and energy efficiency. We preservationists cherish our historic antique/wavy glass windows. In the scheme of things, whole change-out of windows based on energy cost payback is a very expensive and arduous proposition if keeping to the structure’s historical integrity and if done correctly [see HE mag article on John Krigger's Montana home retrofit (http://www.homeenergy.org/article_full.php?id=583)]. Looking at the finished window and wall, John and his crew did a magnificent job.

There is a time and place to change out windows. John mentions in his article that comfort, structural soundness, durability, etc contribute to one’s decision to change out windows. However, for many homes and climatic regions of the country, rehabbing and retrofitting existing windows is the way to go. Krigger, in his Homeowners Handbook to Energy Efficiency, says "If you are considering spending $500 to $1200 per window for the installation of replacement windows, why not consider instead spending $100 to $500 repairing or improving your existing windows.” With today's economy and limited funds, it is viable to save and retrofit the existing historic and period house windows. If done right, I believe 80% or better improvement of a window’s energy efficiency performance can be achieved by WS and thermal mitigation.

I would like to respond to the two blogs: the first on UV and thermal transfer and the second, air/moisture infiltration. I believe both issues have to be addressed, and that the Preservationist and Green and Sustainable movements have a mutual interest in not only saving historic and period houses and their windows and doors, but in establishing a new, verifiable energy efficiency retrofit upgrade standard that results in aesthetically pleasing windows. Furthermore, I feel if we can set verifiable retrofit performance standards, and if the homeowner is part of a 'home performance upgrade program,’ the homeowner should get an energy tax credit for upgrading the windows. To establish the standards, a lot is happening. 

First, thermal issues. Lawrence Berkeley Lab, in collaboration with Building Green, have developed a window retrofit fact sheet that addresses window thermal mitigation applications. The website (http://www.windowattachments.org/)  will also include a third party protocol for field testing and verification of retrofits. Check it out. It's a great new resource!

As for air infiltration, we need to have some verifiable weather-stripping tests to sort out the good, the bad, and the ugly in weatherization of windows that Preservation and green building groups can embrace and promote. I hear that the Mobil Window Thermal Testing Facility (MoWiTT) (http://windows.lbl.gov/facilities/Mowitt/default.htm) is being brought out of retirement. And, Dr. Larry Kinney at the Center for Recourse Conservation has designed and built a testing unit that produced the report "The Effects of Energy Efficiency Treatments on Historic Windows" (EffectsEnergyonHistoricWindows.pdf on http://www.conservationcenter.org/assets/EffectsEnergyonHistoricWin... ). Maybe between the two testing units, protocols leading to standards can be established. For those concerned with insulating weight wells, you will want to get this report.

Finally, the Preservation Trades Network, along with the Window Preservation Standards Collaborative and Kentucky Heritage Council, are sponsoring a National Window Preservation Summit to provide "...definitive energy testing data as well as standards for sustainable window repair, restoration and weatherization" July 25-29th in Pine Mountain, Kentucky (http://www.iptw.org/wpsc_summit.htm). I'll be there as an advisor. As for other window repair resources, John Leeke, Bob Yapp, Duffy Hoffman, and David Gibney all have great web pages, via Google! 

With skilled carpenter/craftsmanship and judicious use of marine epoxy, 'old forest' wood sash windows can give another 100 years of service, if not more. Preservationist and those who want a Green and Sustainable - Home Performance world, need to apply window efficiency up-grade standards to improve a historic and period house window's function, comfort, durability and beauty. 

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Replies to This Discussion

Until people get that their homes are best kept SEPARATE from the outdoor environment, windows will be an energy and durability expensive proposition whether replacing or repairing.  People shortsightedly think they "save" money opening windows.  They think they want the "fresh" air.  Serious education is needed about energy efficient design and operational strategies.  


Air coming through a window is laden with moisture, dust, dirt, pollen... lots of things that make the indoor environment uncomfortable, inefficient, unhealthy, and high maintenance.   Let's not forget Noisy.   


And how many times do you enter a home to find open windows and the AC on?  Examples of operator error abound.  This one is all too common.


If I could have my way I'd say repair old windows, clean them, seal em shut.  Get rid of ugly triple tracks, find and install the beautiful old storms, seal THEM shut too.  Then run an ERV with proper filtration and moisture management for super-efficient, healthy, and comfortable delivery of fresh air. 


Some of the things you say are true, but you have a limited scope.

Personally, I cool my 120 year old adobe home with "fresh" air by opening every one of my wavy glass windows in the evening and closing them before I go to work in the morning. I use a whole house fan as necessary and I don't need A/C. My house is a cool comfortable 65F when it is 100F+ outside.

My point is; every house is different, even the same house can have multiple conservation/comfort strategies that are equally correct.

Free your mind and your work will follow.


Oh contrare, windows are for opening and getting fresh air. Now some people are effected by pollen, and others are dust storms (Google Phoenix dust storm) and some homes might have to much moister, for these issues 'filtered' ERV air might be needed. I do not think you can make a blanket statement that all windows need to be sealed. I for one hate totally sealed buildings. 


As for people leaving AC on, and open windows and or doors, I see it all the time.


By the way, are you in a hot-humid or cold humid climate zone???

David, I share your passion for wavy glass wooden framed windows. The quality materials and craftsmanship of these historic treasures are nearly unattainable in today's marketplace. I am "self-taught" from information gleaned from John Leeke's great website. Most of my competitors are swapping out old windows for new ones with only marginally better performance. I have found that exterior storms on restored wooden windows with an interior roll down insulating shade can far exceed the thermal performance of new Energy Star windows R-3.33. I wish Kentucky was not so far for me, learning first-hand from guys like you and John would be a real treat. This is especially true right now, as we are negotiating to restore 60 8' tall round top double hung windows from the first school built in our valley, which is now serving as a community center.

I just watched an old movie called Hud. The old man tells the kid not to look up to the titular incorrigible Paul Newman; "the world around us is shaped by who we look up to" Congratulations on being featured, you seem to be the kind of guy that more of us should look up to.




I am an energy auditor!   Absolutely, never prescribe without first diagnosing.  We aren't prescribing here, we are discussing strategy.  I'm sorry you feel my strategy is closed minded.  


That said, have you performed diagnostics and modeling on your home?  Your building has tremendous thermal mass.  The amount of BTU's removed in the evening are likely pretty small.   How much do you "save" using your ventilation strategy - do you know?  


Or do you simply assume this is a cost and energy effective approach without having any measurements to back it up?  Have you determined how much do your envelope deficiencies attributable to all these penetrations cost in the heating season?  In my climate heating costs can range a factor of 5-30x cooling cost.  So ventilation strategy saving $1 in cooling may cost $10 in heating.  Since I'm in a humid environment, the latent gain from ventilation may mean purging the house of sensible actually increases a/c load.  Do you track when ventilation makes sense from a total energy perspective, or just vent when it feels cool?


Pardon me if I'm misreading the tone and intent of your post, but doing what you intuitively think is effective and calling yourself open minded, inferring  I'm close minded and should broaden my perspective, seems self-congratulatory, arrogant, and irrelevant.  I want people to save energy and I prefer to see the numbers.  You don't mention energy savings, but maybe you have done then numbers, in which case that's great!  


Do the numbers, and the energy savings will follow.  


An energy auditor, WOW!

Morning Bill, Thanks for the appreciation and your appreciation of 'wavy glass'. I'm self-tought too. John Leeke is a great resource for those seeking restoration knowledge.  I hope this window summit up's the value in saving our historic windows. By the way, what part of the country do you live. I'll get back to all after the summit with what happened.

David, I live in Northern Utah, not too far from the Bay area, so if you ever have a training, I would be very interested in attending.

I also hope the window summit can help people to see the value in their historic windows. It's a constant battle against the replacement mentality that has been fostered by the big window manufacturers. They have misinformed not only the public, but also the legislators, policy-makers and even the guys on the ground(contractors, energy auditors, etc.).

I look forward to your report.


I work (audits and retrofits) mainly in brownstone Brooklyn.  Do you know of anyone who is restoring historical windows in metro NYC who I can partner with?  Thanks.

Afternoon Robert, I do not know anyone in New York, but John Leeke should be able to help. Here is his contact info.  207-773-2306 and http://www.historichomeworks.com/hhw/index.htm



Thanks.  I will call John this week.

My book, Save America's Windows, has a national directory of historic window specialists:





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