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Part II: Conservation FirstChapter 3. Seal, Insulate, and Cover

Insulated Window Shades and Quilts

Night covers that keep glass from becoming the coldest surface in the room.

Difficulty
Intermediate
Cost
$30–80 per window
published

Glass is the coldest large surface in many rooms at night. A quilt or a rigid insulated shade parked against that glass, with the edges sealed, puts a few extra R-values between the room and the outdoors and, just as important, stops the room air from washing the pane. A handsome blanket that hangs an inch clear of the trim does much less. Room air loops behind it, the glass stays cold, and the blanket mostly decorates the draft.

Use a clear interior storm when you want light and a view all day. Use a quilt at night, and open it when a south window should be collecting sun. Leaving a south quilt closed on a bright January day throws away the heat the window was going to give you.

Difficulty

Level
Intermediate
Time
A day to sew or build one window, less once the edge detail is solved
Skills
Sewing a heavy panel or building a simple frame, and fitting a seal

Cost estimate

$30–80 per window

Fabric, a layer of polyester batting or a thin foam that is allowed in this use, and the edge seal. Magnetic strips or a wood stop add cost. A large patio door is above this range.

Materials

ItemQtyNotes
A cover sized to the stop, not just the glass1 per windowIt has to reach a surface it can seal against.
Batting or a declared insulation layerEnough for about R-2 to R-5Polyester batting is a common choice. Do not use scraps of foam board that will sit near a heater.
An edge sealFour sidesMagnetic tape, a compressed foam bulb, or a weight bar that pulls the quilt against the stool and the sides.
A way to park it open1Roll-up, swing-out, or a hook. If opening it is annoying, it will stay closed on sunny days and open on cold nights.

Seal the edges

Heat and air go around the cover through any gap. A seal on the sides and the bottom, with the top trapped in a track or under a valance that actually meets the quilt, is the minimum. A weight in the hem helps the bottom. Magnetic strip set into the edge, landing on a steel strip you have fastened to the trim, is a clean version. Test with a tissue at the perimeter on a windy night. If the tissue moves, air is getting past the cover and the window is not getting the R-value of the batting.

Expect a well-sealed quilt to be worth a few R-points, far less than a wall. That is still a large change on a single-pane window that started near R-1. Do not expect it to fix the wall around the window.

Day and night

On a south window, open the shade when the sun is on the glass in winter. Close it at dusk. East and west windows in summer want the opposite help, and they want it outside if you can, because an interior shade still lets the sun through the glass. The shade guide is the daytime cooling tool. The quilt is the night tool.

North windows can stay covered longer. They were never your solar collector.

A quilt that seals the edgesAn insulated shade covers a window and compresses a gasket on all four sides. A rolled shade above the window shows the daytime position, when winter sun should be allowed in.QuiltEdge sealRoll it up on a sunny winter day
The quilt has to meet the frame. A rolled shade above the window is the daytime position for a south glass that should collect sun.

Moisture and the cold pane

The room side of a tight shade is warmer. The glass side is colder, and moisture can condense on the glass behind the shade. Check on the first cold mornings. If the stool is wet, open the shade during the day, lower the room humidity, or leave a less perfect seal and accept a smaller energy benefit. Do not store a wet wood sash behind a plastic-faced quilt all winter.

  1. Measure to the stop

    The seal needs a landing. A shade that only covers the glass and floats in the opening will disappoint you.

  2. Build the layer and the edge together

    Batting in the middle, a durable face toward the room, and a seal you can repeat on all four sides.

  3. Make opening easy

    Especially on south glass. If it takes two hands and a stool, it will be in the wrong position most days.

  4. Test with a tissue, then with a morning look for water

    Air first, condensation second.

Further reading

These links go to outside sources. This book cites them by link and does not copy their words or pictures.

General education, not a permit or a stamped design. Follow the safety note in the guide, read the safety disclaimer, and hire a licensed trade when the work requires one.