Part 2: What it means to be Net Zero and how this will be achieved in the Hegstad Haven
There are many defining factors that go into creating a Net Zero home, today we will take a deeper look into the home's exterior walls. Firstly you need to create an efficient envelope, this is done with the use of extra insulation, thicker walls, and the reduction of thermal breaks throughout.
To get the higher quality envelope we made a thicker exterior wall, however, we needed to make the construction as affordable as possible. In order to meet this goal we first started with you typical 2x6 exterior stud walls at 16" on-center, as framers can build these walls efficiently. On the exterior side of this wall we have added 2x4's running horizontally at 2' on-center. By adding these we have given added protection against thermal bridging on this portion of the envelope. Next we added a Zip-System sheathing to the exterior instead of plywood and building wrap, doing this does not give added R-Value, but instead gives a much higher resistance to any water penetrating through this layer as the sheathing is factory coated with a water proofing membrane. On the exterior of the Zip-System there will then be a rain screen for added protection against moisture becoming entrapped within the walls. The rain screen also helps to further reduce thermal transfer and since it is very simple to construct it does not have a nominal effect on the overall cost. Finally, there will be hard board added with wood siding to complete the exterior finish. Overall this will make the exterior walls approximately 8 3/4" thick, not including interior drywall. Now, prior to adding the interior drywall the cavity of the wall will be filled with High-Density Cellulose. This was chosen over traditional fiberglass insulation for several reasons, one being that spraying in the insulation coats the 2x6's and 2x4's and all their joints, which is where the majority of your thermal bridging occurs. Another reason for choosing High-Density Cellulose is that it is only 4 PSF. Typical fiberglass insulation is heavier and eventually starts to sag under it's own weight, creating entirely uninsulated cavities at the top of your walls! Lastly, it is made of, up to, 85% recycled materials, helping to reduce the overall carbon footprint of the new home. All this forward thinking will bring the envelope of the home to an insulation value of R-27, rather than the standard R-21, making the exterior envelope of the home very well insulated with little to no thermal breaks and little to no chance for moisture to become entrapped in the walls, which is of extreme importance in our moist climate!