Attic Musings

Cold air revealed via IR camera. Air movement is encouraged by creating a negative pressure environment within the house using a blower door setup

Cold air revealed via IR camera. Air movement is encouraged by creating a negative pressure environment within the house using a blower door setup

There was a period of nearly 18 months during which we worked exclusively on renovation projects in attics. This was not by design, nor was it the result of a new business plan; it was purely coincidental. Each of the homes we worked on during this period had originally been built some time between 1890 and 1940, which is typical in the Greater Boston area. In dismantling the existing attic areas our team uncovered some fantastic original detailing, as well as some construction techniques that left much to be desired. The only thing that was consistent was an inadequate level of insulation by today’s efficiency standards.

During the period that most of these houses were built, installing insulation was not a major consideration during construction. Historically, the heat escaping from the uninsulated walls and roof of a home did a great job of keeping things thawed. It also did a great job of ensuring the residents had to burn a lot of something (be it coal, wood, or oil) to keep warm. Heat was allowed to run up through the walls, into the attic and out, warming and melting the snow on the roof. Much of the heat also escaped through the eaves, which helped prevent ice dams, and also defrosted the gutter. Many homes in New England have split fascia with original wooden gutters that have lasted many decades.

Today, in an effort to conserve energy, insulationu is added to new and old homes to make them warmer and more efficient. Adding insulation to a home originally built without, or upgrading inefficient insulation, is a sound decision, however, one that requires a thoughtful approach. When one changes the original design of their house, and disrupt the flow of heat, they may run into trouble. Thankfully, we are better equipped now than ever before with insulation technology and information.

It is not enough to simply add insulation to a house without stopping the movement of air through the concealed spaces in the walls, attics, basements, and chases. Without air sealing in conjunction with the insulating, a house may still be very inefficient and suffer heat loss and ice dams. Using information gathered by using blower doors and infrared imaging, we can discover how air moves through a house and how it affects temperature. Once the leaks that compromise the efficiency of the home are found, they can be stopped.

Here is a great example of the hot roof method in action. It has been used to successfully insulate and air seal in an attached single family home renovation several years ago. We gutted the entire attic and installed spray foam insulation along the top of the lower walls, and directly on the underside of the roof. We also sprayed the very bottom of the walls around the perimeter of the basement right along the rim joist. This effectively blocked the air flowing into the walls and floor from the basement and rising all the way up to the attic.

Here is a great example of the hot roof method in action. It has been used to successfully insulate and air seal in an attached single family home renovation several years ago. We gutted the entire attic and installed spray foam insulation along the top of the lower walls, and directly on the underside of the roof. We also sprayed the very bottom of the walls around the perimeter of the basement right along the rim joist. This effectively blocked the air flowing into the walls and floor from the basement and rising all the way up to the attic.

It was not possible to address air leaks in the middle section of the walls in this particular renovation. Nevertheless, the end results were striking. In the middle of the renovation project, there was a slew of wintry weather, which was a gift in that our team was able to see the results of our insulation scheme. In the photo below, the left side of the house is our client’s side. The icicles seen on the right side (not our client) indicate heat loss, resulting in melting and subsequent refreezing (AKA ice damming). The side with no icicles or ice damming is the result of properly insulating and air sealing.

It was not possible to address air leaks in the middle section of the walls in this particular renovation. Nevertheless, the end results were striking. In the middle of the renovation project, there was a slew of wintry weather, which was a gift in that our team was able to see the results of our insulation scheme. In the photo below, the left side of the house is our client’s side. The icicles seen on the right side (not our client) indicate heat loss, resulting in melting and subsequent refreezing (AKA ice damming). The side with no icicles or ice damming is the result of properly insulating and air sealing.

What Can Be Done

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In your own home, the results of air flow through exterior walls may be observed through feeling the difference in the floor temperature on a cold day using bare feet on the floor near an outside wall vs. in the center of the same room. In an older home, the difference in temperature is often quite extreme.

Air sealing has been an important consideration in residential work for longer than the 22 years I have been a carpenter. There has been much trial and error on the path to discovering appropriate methods to insulate and air seal an older home. Insulating and air sealing is as much of an art as it is a science (more in some homes than in others).

Newly constructed homes can be designed to integrate insulation into the structure for efficiency. It is fairly simple and inexpensive to air seal in new construction. In remodeling projects on older homes it is much more complicated to air seal. There can be air leaks from areas that are not in the scope of work and one must weigh the cost of addressing these areas with the expected return. At a minimum, it is crucial to address what is accessible and not overlook or disregard opportunities simply because it is difficult to access an effected area. 

In remodeling attic spaces the we have had the opportunity to try different methods of air sealing, the thermal insulation is relatively simple once drafts are stopped. One approach that we found to be very effective is known as “hot roof.” It provides one plane of insulation, the underside of the roof, rather than trying to waeve the envelope around walls, floors, and ceilings. This approach still requires stopping airflow through wall spaces from the basement to the upper levels (AKA "stack effect.") One could run around for days on end caulking and sealing all the seams and penetrations in the top of the walls, which would have great results provided there is access to all the required leaks, and the budget to pay for the labor. In some cases, that is exactly what is required, especially in cases when areas not otherwise involved in the renovation are negatively impacting the efficiency of the insulation. However, we’ve found spray-in-place foam insulation to be a fantastic one stop solution. It both stops the movement of air and it insulates. It can usually be installed in hard to reach spaces, and has the ability to offer almost twice the r-value of fiberglass batts. Its cost to overall efficiency ratio is difficult to compete with as well.

Overall there is no one method that is the perfect solution. Every home needs to be approached with a fresh set of eyes and an open mind while drawing on the past successes and less than successes. The method outlined here seems to work well in the older homes in our area but its critical that we remain observant and honest in the process to figure out where it will not work and where ther may be better, albeit more challenging, means to the same end.