Single-glazed double-hungs w/storms… a good strategy?
We’re agonizing over window choices for our place, which is a 1930s farmhouse. The original windows were double hungs, and at some point a previous owner removed the sash and installed miserable vinyl inserts into the frames. Those have distorted significantly over the years and now leak a lot of air around the sash edges.
Our first thought was to remove the vinyl inserts and the old wood frames and install new wood double-hung units from a manufacturer like Loewen. However, my wife is not sold on insulated glass, because of the 100% likelihood of eventual seal failure and the resulting need to throw out at least the glass if not the sash too. So, she is asking if we couldn’t install single-glazed units that would essentially match the original windows, with storm windows on the outside.
This doesn’t appear to be something I can easily get from a manufacturer, although I have not done much market research. It is, for better or worse, something I could make–I’ve made a lot of sash and windows of various types over the years, and have all the equipment and resources to do the woodworking.
So… my questions. First, what kind of U-factor could I get with a single-glazed + storm detail? I would need to demonstrate to the building department that I am complying with their requirements, which appear to be U = .40 or better. Second, are there proven weatherstripping details for this, and if so, what/where are they? If I do this I want air-leakage performance equal to or better than a good manufactured unit, and I want durable seals that also open easily. I have some experience with the RCT retrofit stuff, but no other recent exposure to what’s out there.
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David - I live in a historic district and couldn't change my 100 y.o. double hungs if I wanted to. I think your idea is kinda nutso, and I mean that in the kindest way possible, but we've done several retrofits with Accurate Metal's fantastic interlock weatherstripping. My local friend Marc Bagala has actually recently put together a video on his very impressive techniques - gimme a shout if you want me to put you in touch with him.
Dan, I'd definitely like to see the video and any other details I can get my hands on. Did you retrofit your windows? Any impressions on how they are for air leakage?
I did do my windows - made a big difference.
Here's Marc's website - http://bagalawindowworks.com/
Brosco has single pane double hung windows with storms in New York and Boston sizes, they are quite common in Vt.. I considered them for my house, but found insulated glass for the same price.
Pella has the perfect window. The interior pane is removable. At least they did twenty years ago when I changed out windows in a customers sun room.
The initial advantage of an IGU versus single glazing is obviously having two panes of glass in a window without needing to add a second (storm) window. The other advantage of using an IGU versus single glazing is the ability to include a LowE coating and gas infill between the lites of the IGU...something I am not going to go into here since Alex Wilson has just spent the past four weeks doing that (really well) already.
Your wife's concern about "the 100% likelihood of eventual seal failure" really should not be a concern when applied to state-of-the-art IGU's.
While IGU's manufactured 20, 30, or 40 years ago were much more prone to failure (including some versions that did have 100% failure by 20 years), pretty much all modern systems have failure rates (some well) below 1% at 20 years. Seal failure and replacing a house-full of windows in a very short time really shouldn't be a concern when dealing with a higher-end company using state-of-the-art materials.
The lowest published number that I am aware of is Cardinal's XL (stainless steel) with about a .2% failure rate, or 99.8% closed seals at 20 years. They predict about a .5% failure rate at 50 years based on their testing and real world experience.
In answer to your direct question, using a clear-glass single glaze and storm will not achieve a U.40, but adding a LowE coating to one of the lites can take you there (depending on the coating), but as a glass-only number. The problem is adding in the sash/frame numbers combined with the glass to stay below the U.40, and then convincing the building department that your numbers are accurate (assuming they are where you want them to be).
You need low-e storm windows, which provides the improved energy efficiency but without the cost or waste disposal of replacing your windows. The Department of Energy is supporting this new technology, and created a new fact sheet together with Peter Yost and Lawrence Berkeley National Lab. Look at the bottom of this link:
One company that sells low-e storm windows is http://www.quantapanel.com
You can also find info by searching for the Alliance for Low-E Storm Windows.
Tom Culp, Birch Point Consulting
You wrote, "If I do this I want air-leakage performance equal to or better than a good manufactured unit."
That will be tough. There are several problems: first of all, if you care about air leakage, double-hungs are a poor choice; you want fixed windows, casement windows, or awning windows. Second, it's hard to achieve low air leakage with homemade windows. This is one situation where a manufacturing facility can achieve better results than a craftsperson building one window at a time.
I received an exceptionally good answer to this question today, from Jud Aley. Apparently the forum software stopped him from posting it here. I am still undecided as to how to proceed here.... but need to settle it soon. Thanks to Jud for this:
"Over the last 10 years we have restored, weather stripped and added storm windows to dozens and dozens of wood single pane windows in homes from Rye NY to New Haven Ct. We have tried all kinds of different combinations for storms and weather stripping. If it were my house, same age as yours, here is what I would do.
Make or buy single pane wood sash.
W-Stripping: While we have installed a fair amount of Accurate weather stripping (Their factory is 25 miles from us) for the last year or two we have been using “Spring Bronze” or “V-Bronze” weather stripping bought from Kilian Hardware ---- http://www.kilianhardware.com/sprinbronwea.html ---- It seems to seal as well or better than the Accurate W-stripping, is a lot more forgiving and takes about 1.0-1.5 man hours to install per window vs. the Accurates 2.5-3.0 Man hours.
If you are going with single pane wood you're going to need to either have weight pockets, tape balances ----- http://pullmanmfg.com/typer.html --- or some sort of “Sash Keep” to hold the windows open, here is a link to a variety of different options
--- If you decide to go with the original pulleys and weights, in most windows, you can pull the interior or exterior casing off and insulate the weight pockets with rigid sheet foam and seal the joints and corners with foil faced tape and spray can foam. We have been able to use anywhere from ½” to 2” thick foam in the weight pockets and it completely stops the air leak in from the pulleys.
The weight pocket insulation is the most time consuming/labor intensive, but some people just have to have the original pulley system.
Storm windows: We have found that White, powder coated, triple track storm windows (Upper glass, lower glass and a half screen that can go either up or down) are the least expensive and easiest to install. Hard core preservationists seem to have big problems with them, but most people don’t notice them once they are in place. If you go this route for a storm window make sure that the brand you buy has a meeting rail cross bar, otherwise the storm frame bulges mid section and leaks like crazy. Here in Ct we buy Harvey Brand Tru-Channel Storms ----
---- The Allied Storm windows are nice, but for the same cost or less you can probably buy or make wood storms that will seal as good or better than the Allied units and will look great. Plus you can order or build them with double pan Low-E glass if you want.
One complaint of the wood storms is that for the warm months you need to swap them out for screens. That is true, but we have found a couple of solutions to this. One is that most people don’t open “all” their windows in the summer, usually just a select few so if that is the case you only swap out the storms for screens on those windows. Another solution is to install this hardware ----
It allows you to prop the storm window open for ventilation and also acts a latch system when they are closed. If you use this systems and insects are an issue you can install one of those expanding sliding screens like this ----
--- When we have clients who think this is too much hassle or the sliding screens look bad, but still want wood storms, we install this type of storm ----
---- Dave will ship them to you or you can make them yourself and source the screen/glass insert locally. We have even installed Bronze screens in this type of storm/screen and it looks fantastic.
Whatever you do don’t use interior storms. I’ve looked at three jobs in the last two years where they used interior storms and in all three cases there were humidity/moisture issues on the inside of the main windows that caused serious rot problems. Plus, inside storms look awful in my opinion and you spend a lot more time looking at your windows from the inside than you do from the outside.
Is this all a lot of work? Sure, but will you ever replace your windows again like you probably will with new double pan windows, No. And you can do all this work yourself or have it done locally so the embodied energy of your final package is going to be much lower than any new double panes.
Airtight and easy to operate = oxymoron.