Summer 2009: Finally addressing vaulted ceilings!

After a few posts on analysis, we are returning to the narrative of what changes I made to my inefficient house to achieve dramatic savings and comfort.
After the early spring completion of the radiant barrier and the subsequent installation of a good chunk of blow-in insulation, my attic efforts were largely complete. The only remaining concern nagging at me was the fact that around the border of roughly half of the house, I had vaulted ceilings that were inaccessible from the attic as well as from the outside. There was no way, short of removing roof shingles and decking and attacking from the top, to install radiant barrier in these areas.
This was somewhat unfortunate, because this was a good 4 feet of ceiling along the outside wall that I could not cover, extending around half the house. Furthermore, two runs of vaulted ceiling intersected over the master bedroom, making that room at best 70% coverable with radiant barrier, unless one were to do something dramatic like replace the roof.
Well! As it happened, a (rather convenient) massive, record-breaking hailstorm occurred in March. The damage from that particular storm damaged roofs in my area severely enough that crews are _still_ in our neighborhood replacing roofs, lo these 7 months later. In fact, they are all over this part of town. (And, in a development near and dear to all of our Energy Efficient hearts, a lot of the new roofs I see are getting ridge vents installed. I do not know if they have investigated clearing their soffit vents or not: perhaps some of them will read this blog and know what to do.)
So, although the insurance deductible payment was not trivial, this turned out to be the year to get a new roof. And of course, since this roof replacement event happens less than once a decade, I wanted to take the opportunity to try to make my changes to the decking over the vaulted ceiling areas.
From the beginning I learned that this was unlikely to be as cost-effective as the other improvements that I had made, mainly because I would be forced to replace existing material in the house rather than simply add to it as I had until this point. The material I had to replace was roof decking; there was no practical way to bring up the old decking without tearing it up. In effect, the extra cost I was paying was because I was giving up decking that probably had another 10 or 15 years of life on it.
The deal I reached with the roofer, who was quite helpful, was this: The new decking was going to cost me roughly $1/square foot. Since he couldn't find radiant barrier decking in the exact thickness to match my existing decking, he was going to supply me with the new decking the weekend before the job. Since I still had plenty of radiant barrier left over, I would construct homemade radiant barrier decking by stapling sheets of radiant barrier along one side of the 4' x 8' pieces of decking. Then the crew would remove the existing non-radiant-barrier decking from the parts of the house that I showed them, and replace it with the new homemade radiant barrier decking. The only cost to me would be the cost of the new decking, which I felt was more than fair.
Another helpful thing about replacing the roof decking is that it would help me resolve another problem that had dogged my attic from the beginning: lack of intake ventilation. As you may recall, I had unclogged all the soffit vents that I could reach from the attic. However, there were many places, all of them over vaulted ceiling, where the vents were still blocked due to the impossibility of getting my body in front of the area to work. Replacing the old decking gave me access from outside, allowing a chance to install baffles on the bottom of the new decking to create airflow where there had been none before.

4'x8' decking with baffles and foil barrier

You can see from the picture above that the combination of radiant barrier and baffles works quite well! I had first stapled radiant barrier to each piece of decking (except the last couple of inches on either end, which were going to be nailed to rafters anyway), then stapled baffles over the top of these, spacing the baffles to where the parts flush to the decking would coincide with the rafters.
To review our radiant barrier theory, the radiant barrier needs an airspace adjoining it to work; having it touch insulation or anything else destroys its reflective properties (recommended is at least a 3/4" space; these baffles gave about 1"). The baffle serves to create that needed airspace. In addition, the airspace is creating a channel to allow outside airflow into the attic from the soffit vents, cooling the attic during the evening hours when the barrier isn't helping. Thus, these cheap Styrofoam baffles perform double duty, allowing the barrier to reflect heat out before it causes trouble, and cooling the heat that does get through by enhancing attic airflow. They are truly an excellent value to the discriminating Efficiency Enthusiast!
The only downside is apparent from the photo: each baffle has a couple of inches running down the edge and through the middle that touch the barrier. These are necessary to give you a place to staple the baffle as well as to provide structural support, but along these runs, the radiant barrier will not work due to lack of adjoining airspace. So for each of these pieces of decking with barrier and baffles, I am probably getting only about 80% of the reflective power of the barrier. Still quite worth doing. I even considered trying to install small strips of radiant barrier along the top of the problematic portions of the baffle, but that would have been a good bit of work for very little square footage of reflection, plus, depending on how much the insulation bent under the pressure of the baffle, these sections might have contacted insulation anyway after installation, making them nonreflective. So I left the decking as you see it in the photos.