A place where one woman has gathered resources and information to help her family survive in an uncertain future; together with occasional personal musings.

Tuesday, March 22, 2011

Insulated Window Covers

One way or another, though, whatever income my readers happen to have coming their way in the months and years ahead is likely to buy quite a bit less energy than the same amount of money buys at present. That makes finding ways to make less energy do more work crucial just now – and that, in turn, leads to windows.

If you’ve caulked and weatherstripped your home, and have a decently thick layer of insulation in the attic, your windows are where the largest fraction of your remaining heating bills go dancing out into the great outdoors. Window glass has an R-value (R means resistance to heat flow, remember?) right around 1 per layer of glass, so a double-pane window has an R-value of 2, or maybe a bit more: that is to say, not much. Interestingly, this is true no matter how fancy or expensive the windows happen to be: you get an R-value of 2 or so from an old-fashioned single-pane window with storm windows slapped on the outside, and you also get an R-value right around 2 from a very expensive vinyl-framed double-pane window with the space between the panes pumped full of inert gas, or what have you. If you want a higher R-value, glass is not going to give it to you.

One point worth taking home from this last comment is that if you’ve got windows that don’t serve a useful purpose, getting rid of them, permanently or temporarily, may be your best option. It takes a certain amount of skill at carpentry to take out a window and seal up the opening so that the resulting wall is weathertight and well insulated; if you don’t happen to have the skills, your friendly local handyperson can do the job in a day or so, and it’s often money well worth spending. If you don’t feel confident in doing anything so drastic, get some rigid-board insulation from your local lumber store, cut it to fit exactly into the window opening from inside, and then cut a sheet of hardboard to fit the same opening, inside the insulation; glue the insulation to the hardboard, paint the hardboard to match the wall, weatherstrip the edges of the hardboard so that you’ve got a good tight seal around the sides, top, and bottom to prevent air leaks, slide it into place and you’re good to go. If you live in a place with cold winters, closing up half a dozen windows in this way during the cold season can save you quite a bit on your heating bills.

What if you want something more easily movable, so you can catch the rays of the winter sun when it’s out but close things up easily at night? Here we come to one of the great forgotten secrets of the Seventies appropriate-tech movement, the fine art of insulated window coverings.

I had the chance to learn about those personally in my teen years. In 1977, my family moved from a rental house in a down-at-heels Seattle suburb to a larger and more comfortable place we actually owned – well, subject to mortgage and all that, but you get the idea. The one drawback was that the new place was expensive to heat, and that was mostly because most of the main floor’s walls facing southeast, toward a stunning view of the Cascade Mountains, consisted of single-pane windows. Insulated window coverings were much talked about in those days of high energy costs and state-funded conservation programs; my stepmother found a pattern, fired up her sewing machine, and made what amounted to a set of inexpensive quilts – faced inside and out with the ornately printed sheets popular in those days, and filled with polyester batting – rigged to slide up and down like Roman blinds. They went up in the morning and down with the sun, and the monthly heating bills dropped by a very noticeable fraction.

There are dozens of designs for insulated window coverings – or, more precisely, there were dozens of designs. It will take you a bit of searching to find them nowadays, as a result of the thirty-year vacation from reality American society took in 1980 or thereabouts. All the designs have certain things in common. The first, obviously enough, is that they put a bunch of additional insulation over the window. How much? A good rule of thumb is that your windows, with window coverings in place, should be as well insulated as the wall on either side – for an uninsulated wall of normal American housing construction, this means around R-5, and up from there as your level of insulation improves.

The second common feature is that the window covering should be sealed around the window, especially at top and bottom. Conventional curtains, open at top and bottom, can actually increase your heat loss by convection: air up against the window glass is chilled and flows out the bottom opening, making a draft across the floor, while warm air gets drawn in through the bottom opening and flows across the glass, cooling as it goes. Stop that "flue effect" and you instantly make the room more comfortable. The insulated shades my stepmother made were pressed right up against the wall above the windows, and had little magnets sewn in along the edges to hold them against metal strips in the wall beside and below the windows; there were many other tricks used to do the same thing.

The third common feature is that the window covering should contain a vapor barrier. Ours didn’t, which meant that the windows were thick with condensation when the shades went up in the morning, and often had to be mopped off with a rag. A layer of something waterproof, on the side of the insulation closest to the interior space, will prevent that, and avoid problems with mold, water damage, and the like.

Beyond these three points, the options are nearly unlimited. It’s entirely possible to use something like ordinary curtains to get the same effect, as long as they have something holding them tight against the wall on all sides of the window opening. Shades were a very common approach, and so were shutters of various kinds, hinged or sliding or even concealed within pockets built out from the walls. One of the most elegant examples I know involved built-in bookcases along a northern wall; there was a gap behind them just wide enough to make room for sliding shutters, and at night the homeowner simply pulled two inconspicuous handles together and turned the window into an R-12 wall.

These same techniques can be used in two additional ways to help save energy. The first is to use insulated coverings inside a solar greenhouse at night. The same clear surfaces that let sunlight into a greenhouse lose plenty of heat at night; equip your greenhouse with some sort of movable insulation to cover the glazing at night, and it becomes possible to run a solar greenhouse much more efficiently in cold weather. The other is the old medieval custom of using cloth hangings, a few inches out from the wall, to insulate an otherwise chilly space. That’s what all those tapestries were doing in medieval castles; insulated wall hangings can function exactly the same way in a modern house, so long as they extend from floor to ceiling on exterior walls, and have both a reasonable amount of insulation in them and a couple of inches of air space between the fabric and the wall.

None of these things are particularly difficult or expensive to make. If you have some basic facility with a sewing machine – and if you don’t, getting it might be a worthwhile project sometime very soon – you can knock together a good set of insulated window coverings for a couple of rooms in a couple of hours, using storebought sheets and some quilt batting as your raw materials. If you know how to handle a saw, a screwdriver, and a carpenter’s square – again, these are skills worth acquiring soon if you don’t have them already – it won’t take any longer to turn some lumber, hardboard, and rigid board insulation into good sturdy insulated shutters.

The time to get these skills, and get your window insulation in place, is now. Just as the inhabitants of dying empires in the past used to listen nervously for the distant sound of hoofbeats that told them the barbarians were on the way, those who are paying attention to the predicament of our own time need to get used to listening for the cracks and judderings of an overburdened system as it lurches down the slope of its own decline and fall. Those faint noises and brief glimpses may be the closest thing to a warning that we’ll get.

1 comment:

  1. I remember greenpa mentioning that what he uses for window coverings is space blankets. He also has velcro along the edges of the windows and along the space blankets, and stores them in labeled bags for the summer. I've often thought of doing that, but still have yet to.