ASK A BUILDER
By CCHRC Staff
The “Ask a Builder” series is dedicated to answering some of the many questions Fairbanks residents have about building, energy and the many other parts of home life.
Q: I am thinking of putting plastic film over my windows for the winter. Is there any value in this?
Yes, but mostly for windows that are old or are in bad condition. If installed well, using plastic heat shrink films can provide three key areas of benefit. Putting plastic film over a window is almost equivalent to adding an extra pane of glass on the window. This could mean up to a 50 percent decrease in heat loss through the glass of your window, but little to no reduction in heat loss through the window frame.
The better your windows, the less benefit you’ll get in using plastic films.
Applying a plastic layer can help limit condensation on window panes by helping to keep the interior window surfaces warmer.
If you can see a haze or droplets of water near the bottom of your windows, this is a sign that your windows could use an upgrade or that the humidity in your house is too high.
Finally, the plastic film can also help to reduce discomfort from cold window surfaces by reducing convective currents that form when air is cooled by the glass surface, causing it to fall and create a draft. If positioned well, plastic films can sometimes be used to help reduce cold air coming in past window edges and seals.
All of these benefits rely on a correct installation method. The common plastic films available at the grocery or hardware store do not insulate by themselves, but instead add insulation by trapping air between the glass and the plastic film. The optimal air gap to create with a plastic film is between 3/8 and 3/4 of an inch.
The seal of the double sticky tape and the window frame surface must be continuous and smooth to trap air effectively, otherwise air and water vapor will move between the glass surface and the plastic film. This will become apparent quickly, as condensation will build up behind the plastic film. This will eventually undermine the point of installing it.
Use plastic on widows that house pets and children can not get to, because puncturing the plastic will ruin it. Unfortunately, covering windows with plastic limits visibility somewhat, depending on the quality of the installation and the lighting. The finishing touches done with a hair dryer are crucial to achieving the best light transmittance, so take your time and work carefully.
Alaska HomeWise articles promote home awareness for the Cold Climate Housing Research Center (CCHRC). If you have a question, e-mail us at akhomewise@cchrc.org.You can also call the CCHRC at (907) 457-3454.