How to insulate skylight windows?

Skylight windows are quite easy to install but some important details like insulation are sometimes overlooked. Warm air usually escapes through weep holes. You want your room to be full of light but also to be warm in the winter and not too hot during the summer. With right insulation, you can be sure the air won’t escape your house.


The best kind of insulator is polystyrene foam. It has a high R-value and good resistance to air infiltration. Don’t use fiberglass or batt insulation because indoor air leaks cause winter condensation. Spray foams are great and keep the warm air inside. You can buy spraying kits and take care of the insulation by yourself. There are usually two tanks with a gun. It’s very important that you remember about eye protection and a respirator. The foam needs to be left for a few minutes to harden, then the excess can be cut off. Flared surfaces have to be covered with drywall or wood.

Ways of insulating the windows

The least expensive method of preventing escaping warm air is attaching a window film to the ceiling. You can install additional films in the light well by attaching tracks around the inside perimeter of the light well. Another option is attaching magnetic plastic storm windows to the ceiling. Installing glass window panes or rigid plastic sheets under the skylight helps as well. It adds a dead air space between the skylight and the windowpane and reduces the movement of window film that results from the change in the air pressure. The light well needs to be insulated in the attic, otherwise, the air will escape through the light well to the attic. You can also attach a hinged foam insulation board that opens during the day and closes during the night. It can be attached to the ceiling.

If your light tunnel is long and has framed walls, you need to apply sheets of polystyrene foam to the insides of your light tunnel frame. It’s best to use two layers. Make sure to seal all the gaps between sheets with spray-on polyurethane foam. After that, cover the foam with drywall. If your light tunnel is short because you have roof windows in the attic, you need to fill the space between wooden framing elements with spray foam. It needs to be applied to the underside of the roof sheathing.