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Community and Q&A

Reuse historic double hung-windows with exterior foam?

kjhkjh | Posted in Green Building Techniques on

We’ve a house in Cambridge, MA which will need total renovation (close to needing demolition!)
The house will need re-siding and windows will need refurbishment (original 6 over 1 double hung)

We want to apply exterior foam (4″ of foam, 2″ of XPS and 2″ of Polyiso) before re-siding and the plan was for ‘outie’ windows (using dudley boxes)

Q. Is it possible to remove and reinstall the original double hung windows or is this unrealistic given their age (1879)? They seem in reasonable condition.

Yes, we could consider innie windows but this is in a historic district and the radically new external appearance might be opposed.

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  1. Expert Member
    Dana Dorsett | | #1

    Yes, late 19th century windows can usually be removed and re-built, tightened up and even re-glazed with a hard-coat low-E glass without changing the look much. It's not cheap though.

    Boosting the performance of antique windows with low-E storm windows also works, and is almost always allowed by those more interested in the local past than the future of the planet if they are interior storms, and sometimes exterior low-E storms will be allowed. I haven't lived & worked in Cambridge for over 25 years now, can't say with any confidence what the current keepers-of-history are giving a pass on. The fact that you're being allowed change the siding is a good sign though.

    On the exterior, skip the XPS, boost the polyiso to 4". XPS is blown with climate damaging HFCs, and loses performance over a handful of decades as those HFCs bleed out, ending up at about R4.2/inch when fully depleted, the same as EPS, which is blown with pentane (at 1/200th the global warming potential, most of which is scavenged during manufacturing and burned for process heat.) Polyiso is also blown with pentane. Even though polyiso won't perform to it's labeled R-value over a winter, the total assembly's performance will beat code-min even when it's 0F outside, and quite a bit better than code min at Cambridge's 28-30F mean winter temperature.

  2. kjhkjh | | #2

    Thanks for your helpful response. I'm thinking of doing much of the window rehab myself (hopefully after some gudance from Boston Building Material workshop!)
    My hobby is cabinetmaking and so I'm pretty comfortable working with wood and rehabbing the windows may be fun (well, at least the first).

    The house is in a historic distribut but I believe that in the context of rahabbing / renovating a house that's otherwise ready for demolition, we may stand a chance of getting through the hysterical commission.

  3. Expert Member
    Dana Dorsett | | #3

    BTW: If the old windows can be truly tightened up, in combination with a tight exterior low-E storm the performance is comparable to a code-min window, even if you keep the original wavy glass (assuming it hadn't been re-glazed with something flatter in the last 127 years.) Reglazing the sash with hard-coat low-E facing the storm window would also boost performance, but not enough to make it "worth it".

  4. kjhkjh | | #4

    You are on the same wavelength.
    Our current house has Harvey TruChannel exterior storms and, in addition, 3/16th acrylic interior storms in some walnut frames that I made for the interior. The combination is very comfortable and likely what I will end up doing to the new house.

    p.s. do you provide consultation help?
    This is a large house (5,000sqft above basement) and I'm considering a multi-zone, multi-unit MrSlim system). Would be great to have a local involved.

  5. jbmnd93 | | #5

    Especially yes if you're a cabinet maker. The only joint work you need to know is rabbets and most of that is going to be hidden in the wall where no one's going to see it. You just need some good reference materials to translate your woodwork skills to your windows. On facebook: Wood Window Makeover, Books: The Window Sash Bible by Steve Jordan. Inspiration: video of a joiner making a sash the old fashioned way, with hand tool:

  6. dankolbert | | #6

    What are you thinking of doing? Making new frames? If the district would allow it, I think you might be better off leaving them alone and extending the sill and frame to the new exterior. The foam overlay would take care of the un-insulated weight pockets. With storms on, the depth of the sashes wouldn't be as noticeable. Accurate Metal weatherstrip and re-glazing goes a long way toward tightening up the windows.

  7. kjhkjh | | #7

    I was hoping not to have to build new frames but reuse the exiting units (I've never removed double-hung windows and have no idea of their structural integrity as they are removed).

    The plan was to remove the windows (by GC or sub) and then I would use a steam box and heat to remove the putty and paint. Then installation of bronze interlocking weatherstrip on the sides, replacement of the weight and balance system with a sprung (pullman-type) tape so that the weight pockets could be filled with polyiso board material). The top and bottom of the sash would also have weatherstripping (final choice TBD)

  8. kjhkjh | | #8

    Hmm, Dan Kolbert, your post about leaving the windows as 'innnies' and using the foam to insulate the weight pockets is a good one. I had not thought about the fact that the exterior storms would mitigate many of the deficiencies of the 'innie' position (e.g. snow accumulation)

  9. dankolbert | | #9

    It would simplify things enormously. The chances of all your windows surviving removal aren't good.

    And the check rail interlock is in some ways the most important part of the system - if you're going to the trouble of doing the sides, I would definitely get the interlock for rails and top and bottom. Not that much more work once you're set up for it.

  10. GBA Editor
    Martin Holladay | | #10

    You've received lots of good advice here. You may be interested in reading the following article -- some of the links on the page maybe useful: What Should I Do With My Old Windows?

  11. kjhkjh | | #11

    Thank you for pointing me to this webpage and for your support on this forum; excellent source of information that's (typicall) substantiated by data and not just point of view ;-)

    I've found a few additional websites on window restoration and bought a couple of books on the subject.

    I'm intrigued by Dan Kolbert's suggestion as to using the storms 'outie' with the (to be restored) double hungs in an 'innie' arrangement. My one concern is what this might look like? Does anyone have pictures they could add to this thread?

  12. dankolbert | | #12

    Wouldn't be that hard to mock it up temporarily on one at your own house.

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