How to Insulate an Attic _ This Old House

The Importance of Insulation and Vapor Barriers in Attics

When it comes to insulating your attic, it's essential to understand the importance of insulation and vapor barriers. As the video explains, once you've finished with the walls, it's a good idea to head up to the attic and fill those rafter bays. This can be done by using a hose to fill the space, much like we see in the example provided.

Insulation is rated by an R value, which measures its resistance to heat movement. The bigger the number, the more insulation you have, and the better it performs. In this case, we have r19 insulation, which is sufficient for most attics. However, if you want to increase the efficiency of your attic, it's recommended to buy a 12-inch thick piece of insulation and lay it on top of existing insulation.

When using insulation, it's crucial to understand how it interacts with the vapor barrier. A vapor barrier always goes to the warm side, meaning that if you heat your house most of the time, the vapor barrier will face downwards towards the conditioned space. If you air condition your house most of the time, the vapor barrier will face upwards towards the hot sun.

The reason we use a vapor barrier is for condensation. Warm air has moisture in it, which gravitates to the cold and condenses. This can lead to condensation getting into the insulation, wetting it, and lessening its effectiveness. It can also cause condensation on the underside of your roof sheathing, leading to rot, mold, or mildew.

Paper is not a proper vapor barrier, despite being around for a long time. Instead, we can use polyethylene vapor barriers, which are common today. However, when laying down insulation and a vapor barrier, it's essential to understand where they meet. If the vapor barrier is not installed correctly, moist air can pass through, leading to problems.

To ensure optimal performance, it's crucial to lay down insulation perpendicular to the ceiling joists. This allows for good airflow and helps to cover up any seams or gaps. By continually packing the insulation tightly against the underside of the roof rafters, you can create a comfortable and energy-efficient space.

When installing insulation, it's also essential to consider ventilation. If you put too much insulation in place, it can become compressed, reducing its effectiveness. Ventilation is critical for most roofs, as it allows air to circulate and prevent moisture buildup. By packing the insulation tightly but not too tightly, you can create a balanced and efficient system.

In conclusion, understanding insulation and vapor barriers is crucial for creating an energy-efficient and comfortable attic space. By choosing the right type of insulation, installing it correctly, and considering ventilation, you can ensure that your attic performs well and lasts for years to come.