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Community and Q&A

Window Restoration and Energy Efficiency

user-7660704 | Posted in General Questions on

I have a small window restoration business in Cleveland. Nationally, the window restoration community is great, and everyone shares methods and ideas. The downside to this communication is that everyone does things the same way, and the MO seems to be to restore everything like it’s still 1920. If you’ve ever installed interlocking zinc weatherstripping, you’ll understand my frustrations.

I’m all about restoration, but I’m finding myself gravitating towards changes that prioritize energy efficiency improvements over making everything look pretty. Old sashes can be retrofitted with modern weatherstripping, and new sashes can be made that incorporate insulated panes while still utilizing the existing frames and reusing as much as possible (it’s also faster to make a new sash then it is to restore it). I am also starting to build rot-proof wooden storm windows (Accoya) that are much more tightly sealed.

I was wondering if the GBA community might have some suggestions for additional avenues to explore regarding window restoration and modernization with an eye towards energy efficiency, sustainability, and maintaining the historic character as much as possible. Any input is greatly appreciated!

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  1. GBA Editor
    Kiley Jacques | | #1

    This is such a good question. Just yesterday, I was talking with the other editors over on Fine Homebuilding about former FHB editor Justin Fink. He does window restoration work in CT, and is a proponent of both preservation and energy savings. He might be a resource to try to tap. His company is Fink & Son Carpentry & Woodworking .

  2. gusfhb | | #2

    Wasn't there a 'This Old House' like 20 years ago where the guys had a machine to cut the old glazing out and install new insulated glass?

  3. Uiloco | | #3

    Exploring innovative approaches in window restoration that prioritize energy efficiency and sustainability while preserving historical character is a valuable direction. Collaborating with the GBA community can yield insights into advanced methods like retrofitting modern weatherstripping and incorporating insulated panes, which align with your goals.

  4. DennisWood | | #4

    One of the guest Youtube sessions on GBA involved a builder who was trying to maintain efficiency with double hung windows. He was doing this, (if I recall correctly) to conform to historical requirements on the retrofit. The solution was not the windows themselves, but adding acrylic inner storms to get to the efficiency level desired. Having used the same methodology for home (where windows are double pane, double hung) and business (triple pane, casement) in climate zone 6A and taking extensive comparative FLIR images at temps in the -20C range, I can attest to how effective these are. The acrylic panels are not inexpensive, but combined with newer (but nevertheless pretty leaky) double hung sliding windows, they raise the overall efficiency to levels of a triple pane casement window. Just throwing this out there if it helps. The difference is not just thermal performance, the acrylic inner storms increase sound attenuation by at least 10 db. vs the double hung sliders in my testing.

    1. user-7660704 | | #6

      Thanks for this. I’m actually installing these this winter in my own home, and it’s something I plan to offer. People balk at it sometimes as it sometimes requires replacing the sash stop trim piece (which is often split and broken to begin with). I like the magnetic strips on the acrylic panels. It makes a nice seal and is easy to install.

  5. Expert Member
    DCcontrarian | | #5

    How do you like working with Accoya? Do you find that it's stable? I've wondered about it for a while, and one thing that turned me off is that it's made from radiata, which tends to be quite unstable.

    Also, I've been unable to find it locally. Do you know how it's distributed?

    1. user-7660704 | | #7

      Accoya is a mixed bag. I see a lot of rotted wooden storms that weren’t maintained, so having something that won’t rot is a nice piece of mind.

      The acetylation process makes the radiata significantly more stable; the shrinkage coefficient is very low.

      It’s pretty good on workability, but because it’s plantation grown and the growth rings are large, you can easily get tear out with the router if you aren’t careful.

      UFP reliably carries 2x rough sawn stock. I buy it through a local lumber yard, and UFP just throws what I need on the top of the lumber yard’s weekly order. It’s also A LOT cheaper than other places I looked. The key is to find a yard that gets UFP deliveries *regularly*. The bonus to this method is that delivery is a lot cheaper, too. The boards are 16 footers.

      The sustainability is also a mixed bag right now in the US. The wood will last a long time, but it is grown in NZ, shipped to the NL for treatment, and on to the US. That’s a hefty carbon footprint. They’re currently building their first plant in the US which will help the product reach a wider audience. It’s slated to be operational in 2024. They’re going to start with radiata, but are working on optimizing the treatment for a domestic species.

      1. user-7660704 | | #8

        Also, if you call Accoya’s reps, they can give you a better sense of distribution in your area. If you find a distributor, they can tell you who gets regular orders from them—Accoya is mostly carried through wholesalers.

  6. rockies63 | | #9
    1. user-7660704 | | #12

      Yes, the 100 year windows are great!

  7. Expert Member
    DCcontrarian | | #10

    I've spent a lot of time scraping, painting and puttying old windows, and I've built a few replacement sashes. And I'm highly dubious that it's possible to retrofit an antique window to be as energy efficient as a new one. The big issue is air infiltration. The glass itself is airtight, and you can seal it pretty reliably, but I don't see a way of sealing wood-on-wood reliably. Wood moves with the seasons, it's hard enough to get a window so that it opens in the summer when it's at its biggest size without it being so loose it rattles in the winter. If you look at modern windows that have wood clad sashes, they're designed so that the wood isn't one of the contact surfaces so it can move freely without affecting the operation of the window.

    So what am I missing?

    1. user-7660704 | | #11

      There are various weatherstripping options that can make them operate better and seal almost all of the draft. That combined with a properly fitted and sealed storm can be pretty efficient. They’ll never be as good as a modern window, but you can them pretty snug. I’ve tried dozens of different types/shapes/materials and there are some that work pretty darn well.

      Silicone bulb at the rails; polypropylene leaf seals on blind stop, parting bead, and sash stops; and felt on the sides of the sash are my current favorite combination. I also add a felt corner at the parting beads on the bottom sash meeting rail.

    2. gusfhb | | #16

      No way to make it a 'modern window'
      I would say that if you:
      Fixed the top sash[I don't remember having one that moved, but I have seen it in pictures]
      The sides and bottom can be sealed from the inside with compliant seals that have enough movement to make up for any seasonal swelling shrinkage. You have 3 moving surfaces, building a seal carrier is not rocket science. I am thinking a 'question mark' shaped seal like every swinging door in the US. Not really designed for sliding, but I have used them as such, and the average window is not opened and closed often enough and the replacement seal is cheap enough that it does not matter.
      The mating seal between sashes as with all crossover seals it a PITA. If you could shift the lower sash inward enough to get a smaller version of that same style seal in a cut kerf in the sash it would seem pretty air tight
      There is a place I bought some nice seals from when I did my 'pretty tight' garage doors that is really good but the name escapes me

  8. user-1112693606 | | #13

    I’m curious what you think of the metal jamb weatherstrip with return flange?

    I’ve used it a few times and it seems to work well. It has the benefit of eliminating the paint-on-paint friction of a sliding sash and providing a good air seal. The sash gets kerfed for the rib. The return angle laps onto the parting bead. Usually I eliminate the sash weight pulley and insulate the sash pocket and install a sliding stop to hold the sash open. A window with operating sash weights is great but in climate zone 6 the winter time air leakage is just too much.

    Still waiting for vacuum insulated glazing. If that ever comes to market we’ll be able to have cake and eat it too: true divided light windows with great u values.

    1. Expert Member
      DCcontrarian | | #14

      Can you tell me more about the sliding stop?

      Your comment about the sash weights is kind of what I was getting at in post #10. I don't mean to be Contrarian, but old-school windows just weren't designed to be air-tight.

      1. user-7660704 | | #15

        I’d be curious to hear about the sliding stop as well. Or are you referring to spring bolts?

        The metal weatherstripping works well, it is just a bit of a paint to install, old sashes frequently have damaged slots, and it adds a step in removing sashes for maintenance or cleaning, unless you know what you’re doing, which most painters don’t.

        Also, vacuum glazing is available. Call Tom O’Day at Pilkington and ask for the spectra glass.

        1. user-1112693606 | | #17

          Yes, sorry, spring bolts is what I meant, although I like the ones without the springs .

          Thanks for the VIG lead. Is that “Spacia” instead of “spectra”? I heard about a few demonstration projects but I guess it’s available? Have you used it?

          1. user-7660704 | | #18

            Yes, sorry, Spacia. I haven’t used it yet, but plan to on my own house as a test. I have a sample, though. There are a few caveats summed up nicely on this website:


            The dots aren’t too noticeable unless you’re right next to the glass. The plastic piece is more noticeable, and I think it’d stand out like a sore thumb if used in a multi-lite window. There is also a minimum size, which can potentially be limiting. It’s a great step in the right direction, though.

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