Sealing the Ceiling

Now that the exterior walls are done, it’s time to start sealing up the house and insulating it for winter. The walls are still drying, so the next step is the attic space.

At the Midwest Renewable Energy Fair this year, I had the pleasure of meeting Rob and Shirley Pichelman. They live near Richard Flatau’s house in Northern Wisconsin and have built their own cordwood house. Besides Rob’s excellent blue print design work, he also mills his own lumber. He informed me that he had some nice 3/4″ cedar tongue and groove planking for sale. So, I took him up on his offer and both Rob and Shirley stopped by last Saturday to drop off 1,500 sq. ft. of cedar planking. The cedar was cut right on his own property from a tree that was at least 125 years old. The cedar is quite beautiful and will make a great ceiling for the second floor living space as well as our master bedroom on the first floor. Although you hate to see trees harvested, at least you know that it was done selectively without any major impact to the forest.

Besides the planking, I had to make a decision on what to use for insulation in the attic space and to decide if a plastic vapor retarder was warranted.

I’m not quite sure if the vapor retarder debate will ever end. There are varying opinions to using a vapor retarder between the ceiling and attic space and I re-explored this issue just recently.

It all started when I purchased 84 bags of insulation. I bought it at Menards and I did save “Big Money at Menards” by purchasing it on sale. It was about a dollar off per bag. Anyway, I decided to check out the manufacturer’s web site and to my chagrin, they suggested not installing a vapor retarder. They didn’t explain why, just that it wasn’t necessary.

Being the curious type, I called their headquarters to find out why it wasn’t necessary. It was explained to me that the cellulose insulation blocks air infiltration and allows moisture to diffuse through the cellulose. If I did put on the vapor retarder, I ran the risk of condensation forming on the plastic and rotting my ceiling. I asked how was condensation going to form on the plastic if I was going to install 18″ of cellulose up in the attic space? The temperature of the plastic sheeting should never reach the dew point, if there’s R-60 worth of insulation up above it. The kind fellow on the other end of the phone couldn’t explain that one and just answered my question by stating that if it was his attic, he wouldn’t install a vapor retarder.

I was not satisfied with that response and decided to call Oak Ridge Laboratories in Tennessee. The engineers at the laboratory have always been willing to answer my questions regarding the energy efficiencies of insulation and thermal mass, so I figured I would give them a call. (Last February I spent about 45 minutes with them on the phone discussing R-values of a cordwood wall and the thermal mass issue. After that discussion, I am quite confident in a R-value of about R-1 to R-1.5 per inch of cordwood wall.)

After I explained my case, they asked a few questions about where I was building, type of house, etc. Right away, I knew I was going to get a more thorough evaluation of my project. Based on the climate in SE Minnesota, along with my intended R-60 for the attic space, the engineer concluded that a vapor retarder would be beneficial. He explained that during extremely cold conditions, it would be best to keep as much moisture from penetrating the attic space as possible to prevent any condensation/frost from occurring above the insulation. The kind engineer concluded by stating that if it was his attic, he would install a vapor retarder.

So, now I had to weigh the two answers. But before making my final decision, I researched the Internet for more opinions. The best one I found, I think…explains it the best. So instead of reiterating, here’s a link for those who wish to read more: http://www.buildingscience.com/resources/roofs/ceiling_vapor_barrier.htm

A Barn Swallow’s eye view of the attic space. The vertical insulation screen is 18″ high to prevent the insulation from going out to the eves where it is not needed. The vertical screen does not go all the way up to the underside of the roof, thus leaving space for ventilation.

To make a really long story just long, I decided to go with the vapor retarder. The vapor retarder that I am installing is 6 mil plastic. I purposely call this a vapor retarder because it’s not 100% sealed. There will always be some holes due to staples, nails and seams, but 90+% is fine with me. It should greatly reduce the amount of air/vapor penetration into the attic space and keep the living space warmer in the winter.

There is one section though that I decided not to run the vapor retarder and that is the attic space directly over the double cordwood cavity. I do want the walls to breath—especially while the inner walls are drying. A vapor retarder at the top of the walls would substantially slow down the drying process to the point where “fungus amongus” might be a concern. The temperature in between the walls will be lower too, so it’s probably best to insulate, but not seal the wall cavity. (The inner side of the outer wall will be spray foam insulated this Fall.)

Other Things to Consider
The attic space is the most critical aspect to the home’s energy efficiency and for that reason, I am taking special care to keep the number of ceiling breaches to a minimum. In our case, the wood stove chimney, vent stack, electrical boxes for ceiling fans and whole house fan comprise all of the breaches in the attic. Bathroom fans will be vented out through the walls rather than the attic space. All interior walls will be framed under the ceiling instead of through the ceiling.

I do find myself doing a juggling act with all the things that have to get done this fall season. I’m at a point where I can’t do anything other than ceiling joist framing until I get the electrical service roughed in. Which brings me to my first meeting with the electrical inspector.

Meeting the Electrical Inspector
I had asked for his assistance to understand how to proceed with obtaining a permit, and found myself lighter in the pocketbook after his arrival. Things started out on a rather strange note with his arrival late in the afternoon last Wednesday. He drove up the road and instead of stopping at the house drove all the way to the pole shed located about 700 feet from the house. So…I had to run down the ladder, and down the road after him. Once I caught up to him and explained where the house was, he turned around and headed back up the road with me in hot pursuit. By the time I caught up to him, he decided to nose around a bit and lifted up the cover to the temporary service panel located out by the electric meter. Now I rarely have a need to lift up the door on the panel, so I had no idea that a rather large nests of wasps had taken up residence under the door. All of a sudden he started running away from the panel with wasps in hot pursuit and of course, he got stung. (At this point, I’m thinking to myself this is not going very well.) I apologized for the wasp nest (like I had any idea it was there and had trained them to sting on his arrival) and he assured me that at least he wasn’t allergic to wasp stings.

We then proceeded to the house and I explained all about the cordwood house and explained to him that I hadn’t covered up any electrical fixtures except for mortaring in 7 electric boxes for external outlets and light fixtures. He didn’t seem too happy that I had already mortared over the boxes, but he could easily see that the conduit ran directly from the boxes through the mortared walls.

I informed him that I wanted to get him involved at this point because I was just starting the attic work, which would mean electric lines would need to be run through the attic space for five ceiling fans and a whole house fan. I explained that I was also going to use conduit throughout the project. Conduit is not necessary in Minnesota, but it gives me the flexibility of changing the wiring without tearing apart cordwood walls.

I asked him a few questions, he reviewed my plans and seemed quite satisfied. Then he started filling out the paperwork for the permit. I wasn’t sure how much it was going to cost, but I knew he wasn’t going to go away without a check in hand. He informed me that the electric permit cost $80 plus, $20 for a rough-in inspection and $20 for final wiring inspection. So far, it seemed pretty reasonable. But… then he informed me that since I was doing the electric work in segments that it would cost me $20 for every trip he has to make for rough-in and wiring inspections. My total for his first trip out was $101.00. $80 for the permit, $20 for inspecting my rough-in electrical work in the exterior cordwood wall and $1.00 for writing up the paperwork. I’m sure the electrical inspector and I will become good friends before this project is complete and I’ll have to keep the checkbook close by for his next visit(s).

The next few weeks will find me busy framing out the attic space and installing electric conduit lines. I’ll keep you informed to my progress.

The glow from a “scrap wood” campfire lights up an oak tree by the cabin.