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Community and Q&A

Window historic preservation issues

mike keesee | Posted in Energy Efficiency and Durability on

Our local historic preservation committee will not allow retrofits/replacement of so called historic windows – the aging, single-pane, wood frame with “wavy” glass. Some in the historic community claim that the existing windows can be retrofitted with films, weatherstripping, insulated shades or the like and match the performance of a high performance (e.g., energy star rated) window replacement. Unfortunately they don’t respond well to arguments based on the laws of physics and I’m asking if anyone has more specific “studies” – the historic types want studies – that show the quantify the benefits (not only energy savings, but improved durablility, reduced maintnenace, etc) of replacing historic windows vs. apply window film, etc. approach. Any help would be greatly appreciated.

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  1. user-940291 | | #1

    As it turns out I just spent the last couple of hours trolling NFRC's data for specifics on the performance of a single-glazed wood window with a combination storm window applied. Data my Marvin Windows supplier was able supply shows that a double-hung with 1/8" clear glass separated 2.15" air gap from a single Low-E combination storm window has a U-factor of .35. That's 25% less efficient than the .28 U-Factor you can pull from a lot of mainstream insert windows with double-pane Low-E4. The data I'm seeing says that the folks who think the retrofit will meet current standards are incorrect. If you do find research somewhere on the topic please follow up here. You're not the only one going through this for sure.

  2. smalld | | #2

    I would say you are on the right track - the Marvin Ultimate Insert Double Hung- if that is in fact the type of window you are after in this specific instance; does offer an large array of sizes and configurations,clad and unclad. They easily out-perform the suggested storm window configuration that you have been quoted.The man-hour and materials costs significantly decreased and offset the increased costs.They range from approximately .21 to .45 u factor and with SHGC's from .16 to .56. Please remember that higher SHGC's can markedly offset the lower U values of windows and glazed doors depending upon both the specific climatic factors and the orientation of those glazed units. I have used them very successfully here in residential heritage home energy retrofits north of the 49th.

    small d
    being human on a small planet

  3. user-659915 | | #3

    I'm going to give a counter-argument here and suggest the 'historic types' are not all full of hooey. The laws of physics, when consulted on the big energy picture, tell us that for a historic building (with usually rather limited fenestration) glazing U-factors are a relatively minor consideration compared to all the other usual energy retrofit suspects. Furthermore, by saving manufacturing and transport costs, weatherstripping and renovation of the existing sash is often a greener option than complete replacement. Fine Homebuilding had a great article a couple of years ago on the best way to go about this. And finally, the laws of economics consistently tell us that window replacement is about the least cost-effective way of improving energy performance in an old building, with a payback period generally exceeding the projected lifetime of the unit.

    Yes, old windows have a maintenance penalty compared to high-end new ones. The same could be said for your home as a whole. There's nothing to stop you having the latest and best in high-tech energy efficiency in such replaceable items as your refrigerator and your furnace. But If you actually have 'wavy glass' in your windows this suggests your home is a hundred years old or more, and looking at it as a precious and increasingly rare resource - you must appreciate that to have bought it in the first place - there's a good case for leaving your irreplaceable historic windows as part of that whole fabric.

  4. user-963050 | | #4

    Biggest improvement you can make to your existing windows is to get them tightened up (i.e. air tight).

    The single pane glass, even with a Low-e storm, will not approach the performance of a double pane insulated, Low-e/argon won't look as charming either.

    The wood used in the older windows is old growth timber and usually very durable. I would stay with what you have and get them retrofitted for a good air seal. Once that is done, look at insulating the attic and other improvements first.

    As mentioned, the relatively small amount of glass does not give you a real good ROI for expensive windows.

  5. gusfhb | | #5

    Stopping people from replacing nice old windows with cheapo vinyl windows is a good thing.,

    Allowing self appointed historical committees to trump energy codes is a travesty.

    There is really no low budget answer to your problem. Committees created to save important buildings from destruction instead decide what color you may paint your house, while it is nestled between one with aluminum siding and one with asbestos.

    At the end of the day, turn your old windows into bad storms. Mount a single pane low e inward swinging window. I don't think you will win against the historical com, so you need to go around them

    Some 20 years ago there was a guy in This Old House who had a whole setup in a truck to rout out old glass from antique sashes and install thermopane, He would then install vinyl[IIRC] glides and remove weights. Maybe not state of the art, but better

    Don't listen to those who say you don't lose heat through windows, do the math yourself. A house full of R1 windows can lose more heat than a whole roof

    Air seal and insulate first of course.

  6. user-659915 | | #6

    Responses to Keith:

    "Allowing self appointed historical committees to trump energy codes is a travesty."

    It's almost always possible to a comprehensive better-than-code energy upgrade to a historic home without removing irreplaceable old glass. The National Park Service has some excellent guidance on how to do this. The key to working with a historically significant building is reversibility. If your intervention turns out to have been a terrible mistake, can you put it back the way it was? This is why cellulose attic insulation is preferred to spray foam, and open cell spray foam to closed cell. We're all fallible, and destroying the historical record does nothing to improve our knowledge about what makes good (green) building practice. I know it's easy to get worked up about local committees that may on occasion be extremely misguided and ill-informed but let's not assume they have nothing important to contribute.

    "At the end of the day, turn your old windows into bad storms. Mount a single pane low e inward swinging window."

    Now we're talking. This is not a bad idea, and it's been employed by preservationists on some very significant historic buildings. It doesn't have to be just single single-pane either.

    "I don't think you will win against the historical com, so you need to go around them."

    Instead of going around them, how about working with them, and educating them.

    "Don't listen to those who say you don't lose heat through windows, do the math yourself. A house full of R1 windows can lose more heat than a whole roof."

    No-one is saying you don't lose heat through windows. And I'm pretty sure you'll never achieve passivhaus standards without at least high-end double pane. But if that's your target, why start with a historic home subject to these kinds of restrictions? There's a much, much vaster supply of crappy mid-to-late twentieth century homes begging for deep-energy upgrades. And you can still do a pretty damn good job on a house full of R1 windows if you pay attention to all the other elements. Net-zero, probably not. Better than current energy code, almost certainly.

  7. gusfhb | | #7

    RE: James

    I agree with what you say, a few quibbles:

    Actually you kind of did say that windows don' t waste much energy

    the measures you describe are absolutely perfect for historically significant buildings.

    Unfortunately every single historic commission confuses 'old' with historically significant.

    In my area pre revolutionary houses are quite literally a dime a dozen. Most were built by Ed the barrel maker and George Washington never slept within a days ride of them.

    They should be saved

    But preserved?

    better rip out all that pesky electrical see my point.

    The national register for historic places is the right venue for talking about saving historic framing details, not downtown East nowhere, where Mr Smith has a job to keep him out of Mrs Smiths hair at night, deciding what color is historically accurate, what level of gloss.....this is the more common scenario than anyone ever ripping the walls out of a 200 year old house to learn about it's framing techniques.

    The house I lived in from 85-96 was ~200 years old, Indian shutters, 5 fireplaces. The house diagonally across 210, 2 houses down over 200, 4 houses down 300 years. Two houses the other way 150, 150. Thank god we have no historical commission[being we were in the sticks, 4 miles from the historic district] we never would have gotten anything done.

    I still drive by a house in downtown Salem that has curved sashes with curved glass[2 over 2, mid 1800s I guess]. It would be a mortal sin to replace those, but force them to keep them..........

  8. user-659915 | | #8

    Hey Keith:
    I take your point that there are a few places in the US where century-old plus homes are a dime a dozen, we're not so lucky around here. I also agree historic oversight committees can be difficult to deal with. They tend to see the world from a very narrow perspective. But so do we, and with our close focus on technical specs we can sometimes miss the forest for the trees. There's a very good reason why this site is not called 'Net-zero-energy Building Advisor: there's more to green than energy performance, which is why we see here so much thoughtful discussion to balance the high R-values of hydrocarbon foam insulation against the better environmental footprint of cellulose, for example.
    The old-window issue requires a similar balancing act. Sometimes replacement IS the best choice, but repair and re-use is a good green option, where the lower environmental cost can often outweigh the marginal benefit of super-low U-factor in a singular building element. When we consider that our older buildings were built to function in a pretty low-profile energy economy there should be no reason for historic authenticity and green renovation to be at loggerheads.

  9. user-659915 | | #9

    Post-script -

    having been mostly away from GBA for a couple weeks I only just now came across this very recent post by Carl Neville on exactly this issue. Definitely a propos:

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