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Insulating the Attic

Normally, we wait until the end of a project to summarize "do it yourself" stuff, but recently we've been getting good advice from readers and there's no sense in waiting until after the fact to get more ideas.

The Challenge
We've finally gotten to the insulation phase (horray! < This is a combination of "horrors!" and "hurray!") for the second floor. I've insulated the walls over several weekends and have now started to insulate the attic and ceilings.

The challenge around insulating the attic is twofold: first, the higher ceiling in the master bedroom leaves relatively less room for insulation. Second, the main attic space criss-crossed by the air conditioning ductwork from our Unico air conditioning system.

Our Approach
First, we researched the recommended insulation levels for our climate. This information is widely available, including at the point of sale in stores where you can purchase insulation. The government's EnergyStar website has a simple summary here. They recommend that a Chicago home have between R-38 and R-49 for ceiling and attic spaces. (The R-value rates how well a material insulates. A higher rating indicates more insulation.)

Selecting Materials
There are a myriad of insulating materials to choose from, with many newer 'hi-tech' varieties cropping up in recent years. One way to categorize the types of insulation is by the methods of installation: rolled material insulation (primarily fiberglass) is the most common; 'blown-in' insulation is very popular for existing homes because it is so flexible; 'sprayed on' varieties of insulation are frequently used in new construction and commercial applications; and rigid foam materials are good for getting higher R-values into tight spaces.

We chose to use a combination of rolled fiberglass and rigid foam. The rolled fiberglass represents the majority of the insulation we are using, with the rigid foam solving a specific problem at the peak of our cathedral ceiling in the bedroom. We wanted something that we felt confident in installing ourselves, that would fit the space, would create the cost savings we were comfortable with, and which was affordable.

When would you choose one over the other? The following factors are considered when choosing insulation:

-Space available for installing insulation
-Cost (cost of insulation/installation vs. savings gained over time from insulation).
-Specific characteristics of the space being insulated (ventilation, above ground, below ground, wall, ceiling, exterior, interior, etc.)
-Ease of installation for your specific application
-Personal preference for specific material-types

The Department of Energy has a helpful primer regarding insulation types and decisions. There are MANY different opinions regarding insulation AND ventilation, with no consensus among home professionals as to the BEST type and technique. So, learn as much as you can in order to make an informed decision for your specific situation.

Installation
First, I tackled the higher ceiling. There is a partial vault in the front bedroom dormer, with a 2 foot high, 3 foot wide space at the peak that accomodates the AC ducts. (Actually, we prefer that look to a fully vaulted peak anyway.) For a majority of this ceiling we used rolled batts between the rafters. That space only allowed for using R-30 while preserving the ventilation we needed, a bit below the government recommendation. At the peak we're using foam board because space is so tight we couldn't get much more than R-20 with fiberglass. Stacking foam board with an R-value of 10 should allow us to exceed R-38. I haven't gotten to install this yet but I hope to soon.

The ceiling above the second bedroom and the bath is lower, so there is plenty of space in the unfinished attic for meeting the recommendations using fiberglass. However, installation is tricky because the AC air handler and the main trunk line circle through the entire space. I decided to tackle the space as three layers:

• Kraft-faced R-13 - Typically for walls, this was actually a useful first layer because it is the same depth as the 2x4 ceiling joists. Our joists are roughly 14 inches apart, so common 16-on-center insulation was inexpensive and I was able to cut and staple it into place quickly.
• Unfaced R-25 - This sits on top of the first layer and covers the tops of the joists (wood conducts heat and moisture and covering the top of the joists cuts down on this). This is where the AC ducts become a challenge, so there is a lot of cutting involved to achieve a proper fit. The nice thing is that the R-25 is roughly the same height as the AC trunk line--about 8 inches. This will create another even surface when the R-25 is laid next to and around the ducts.
• Unfaced R-11 - This final layer rests across everything and will run uninterrupted across the whole attic space. This provides a protective layer over all of the AC ducts, so it should help prevent any loss of cooled air traveling through the ducts on the hottest summer days in the attic.

I'm not finished with this yet, but here's an in-progress photo showing the first two layers amidst the AC ducts.

The attic ultimately achieves close to R-49, although I know some of this benefit is cancelled out by the lower value of the insulation above the front bedroom. We can help to influence this by closing the door to that bedroom when the air-conditioning is not in use--the main attic then serves as the highest point of the house, adjoined to the first floor by the stairwell.

Special Considerations
There are a few additional unique things we're planning that are worth pointing out:

• Because the AC trunk is in the hottest part of our house (a necessity), we're concerned about insulating it from hot attic air during the summer. Although the ducts themselves are wrapped in foil and some insulation, we wanted to increase that. We found a useful product from Johns Manville called DuctWrap, available at Menards. It is foil-faced so it will reflect radiant heat from the sun that penetrates the roof.
• Our air handler is also in the attic, so it will require some space on all sides to allow for air circulation. We're expecting to build some sort of box around it with rigid foam.
• I'm sure someone will wonder why we didn't used blown-in insulation for the attic given all these obsticles. Our main concern about any loose material was its possible interference with our attic ventilation system over time.
• Before we began insulating the attic, Jeanne suggested checking the AC trunk line for air leaks (the trunk is installed from a series of joined pieces taped together with a special reflective heat tape). We found and sealed several small leaks...we will create a separate journal entry to explain why and how we did this.

So, there you have it. Given that we're not done yet, suggestions are welcome. We expect to finish up insulating in the next two weekends (except for the bathroom, which we've delayed pending some of the other work we are doing there).

Posted by aaron on November 13, 2004 at 8:15 AM (4)

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