Building science

Building Science 101

Building Science 101 by the Insulation Institute is a really good primer to get up to speed on building science. Pay particular attention to the discussion about moisture movement and control. I am sure you will find information on how moisture moves that you did not know about. This is a good companion to the perfect wall, and a good place to start if you know nothing about building science.

The Perfect Wall

Dr. Joseph Lstiburek is one of the giants of building science and performance. He has developed what he calls the Perfect Wall. There are variations to Dr Lstiburek's Perfect Wall. One of them can be found here.

The DER work we did under the NYSERDA grant is also a variation on the perfect wall. One important goal of the NYSERDA DER project was to keep the cost of the DER below $10 per surface square foot. We eliminated the vapor and air control layer under the two layers of Dow Tuff- R polyisocyanurate insulation to help keep the cost down. The reasoning is that the existing structure is open enough to the inside that any leaks will dry in. below is an explanation of how it can be done.

  • Make the structure air tight. Small leakage paths let in huge amounts of air when the larger holes are closed. Air is compressible and loves to move fast and the forces driving infiltration and exfiltration remains unchanged.
  • Mind the moisture. As the air leaks are closed up, moisture issues will be exacerbated, as water and vapor no longer leave the building. Elimination of moisture entry into the building is a must.
  • Place the insulation on the outside of the building. Use at least 2 layers of sheet insulation, such as Dow Tuff-R, with all seams taped. The outer layer will protect the inner layer from the weather, extending the useful life of the assembly significantly. As Dr. Lstiburek says, “wear your sweater, don’t eat it.”
  • Have a functional drainage plane. Using furring strips on top of the Dow Tuff-R secures the insulation to the building and provides a great drainage plane. They also provide a way to fasten the exterior cladding.
  • Be attentive to the small details. The water, air, vapor and thermal control layers have to work in conjunction with each other, make sure they are aligned and complete. Think about what will happen when the hurricane hits.

Deep Energy Retrofits of Historic Homes

When renovating an older building, preserving its appearance is important. So is updating its mechanicals. This article by Betsy Pettit shows explains how to approach Zero Net Energy by updating the enclosure while honoring the historical nature of the building. It is well worth the read.