This quarter was all about air leakage and energy efficiency. In order to have an energy efficient house you have to cut off the air leakage. This keeps the conditioned air in the house that you have paid so dearly to heat. After the air leakage is cut off then ventilation air is the concern. Living beings, like people, need fresh air to breath in order to be happy, healthy, and productive. The following is the process of events leading up to the present state of efficiency for the little house.
We passed our frame inspection and started to install insulation and sheetrock. Everything on this house has been a bit of a trial and the insulation was no exception. As part of the science of the building we were testing for air leakage at each stage of construction. We first installed the insulation and sheetrock in the ceiling portion and then ran a blower door test, the result was 15 air changes per hour at a negative 50 Pascal air pressure. I was hoping for better, it seemed as though the exterior walls were not as much of an air barrier as I had expected.
Next was to insulate and sheetrock the walls. We used dense-pack blown-in insulation in the walls that was held in place with netting until the sheetrock could be installed. This insulation was chosen because the wall cavities could be filled fully without the voids and compressions that can be the result when using fiberglass batt insulation. The insulation and sheetrock went up and another blower door test was conducted. The result this time was 8 air changes per hour at a negative 50 Pascal air pressure. This number is better, but still not what we are looking for in an energy efficient home.
What can be done now you ask? Well we started to tape and mud the sheetrock. All ceilings, walls, inside corners, outside corners, transitional areas, and intersecting walls were tapped and coated. At this point we thought we for sure were going to have built the equivalent of a thousand square foot thermos on a foundation. The blower door test at this stage showed 5 air changes per hour at a negative 50 Pascal air pressure. We are still not at the 1 air change goal that we all thought we were going to be able to achieve.
So now this is getting frustrating. One thing we noticed when conducting the leakage testing was the amount of air leaking through the penetrations in the envelope. Every hole in the envelope was contributing to our very significant leakage number. I went to the hardware store, bought caulking, cover plates, insulation pads for under the cover plates, and some blue tape to cover holes that couldn’t be managed with cover plates.
We covered most everything we could find and the result was to bring the number down to 3.5 air changes per hour at a negative 50 Pascal air pressure. OK, so now were starting to approach an acceptable number. What this shows us is that the devil is in the details, and not just at one spot, but through the entire construction process. We still have some air leakage in the attic areas to seal up and I am confident that once that is done that we will be very close to our goal of 1 air change per hour.
Another thing we were very pleased to discover was that our heating system is totally within the thermal boundary, which is as planned. The significance of this feature is that if by chance there should be any leakage from the heating system, it doesn’t leave the conditioned air space. Hence, there is no leakage of heated air to outside. This house holds all the air it heats.
Once again I would like to thank all the students for their continued support and enthusiasm towards the project. Without their hard work, critical thinking, and creative ideas this project would not be able to proceed and be successful. I will leave you with a few more pictures of progress and fellowship.
Good by and good building,