8 General Guidelines for Creating a High-Efficiency Home
Updated: Aug 22, 2019
1. A TIGHT AND HIGHLY INSULATED HOME BEFORE CONSIDERING RENEWABLE ENERGY SOURCES
Too many people are seduced by solar arrays and wind turbines. If you care about your environment, focus first on getting your house right so that it won’t NEED a lot of energy to keep you comfortable. Focus on an air tight and a super-insulated shell of your house. (R-40 walls, R-60-80 ceilings) triple pane windows. Air Changes Per Hour at -50 pascals depressurization at or below 1. This is how we measure the tightness of a home. Fulfilling these goals creates a low energy demand home and is the most affordable and durable approach to building a highly efficient home. If you are trying to have a home that costs nothing to keep you comfortable (Yes this is possible and it is called Net Zero) This approach will get you there. It is proven to work. These houses will last a lot longer than your new solar panels.
Your house loses heat in a similar way to your body. Here is the correlation.
The thick sweater you wear under your shell or windbreaker is insulation. In building science, we call it the “thermal boundary”. It traps heat near your body. Your house’s thermal boundary is the insulation that you have in your walls and in your attic. Sometimes this is fiberglass, cellulose, foam, newspapers in older houses or mineral wool. Houses can have many different insulation in their walls depending on when they were built. Some older homes have no insulation at all.
On your body, your windbreaker is the air barrier. It stops the wind from robbing the heat your body worked so hard to produce. We also call this “air sealing” or “air leakage”. Imagine your windbreaker is full of holes. It will feel drafty and uncomfortable especially where the holes are. The air barrier in your house stops the heat from passing through the thermal boundary and escaping to the outside. When we do audits we regularly find MANY holes in the air barrier in a home.
2. Moisture is Always an Issue with Tight Houses
We employ many materials from lumber products, to gaskets, to tapes, adhesives and high tech sheets of fabric to manage water vapor and the negative impact it can have on our high performance homes. Be sure that your builder truly understands how moisture works and moves in a high performance home.
3. Have a Full House Integrated Air Exchange/Heat Recovery Ventilation System
If your home is high performance it needs balanced ventilation to breathe. THIS IS MANDATORY! This will foster excellent indoor air quality including excellent moisture/water vapor control.
4. Heating/Cooling and Hot Water
Heat pump hot water heaters work! Part of a low energy demand home before solar. Check out the multi head mini split heat pumps to heat and cool your home that are available. We have installed many of them and they are successfully heating and cooling homes for a dramatic fraction of the costs of any other options.
Keep your window glazing to the south and include about 10% of your total wall square footage for south facing glass area. Have windows in the 0.16-0.18 U factor range and 0.6 or more solar heat gain coefficient (SHGC). Use lower SHGC on east, north and west sides to gain lower U-factors (Higher R values for glass).
Completely insulate your foundation/slab from the footings on up and make sure your air barrier follows the thermal envelope completely from under the slab all the way to the roof and is continuous with no breaks.
7. Roof Trusses/Rafters
Make sure you have adequate raised heels for your trusses/rafters above your top plates of your walls- 12-18 inches minimum so that the top of the walls are adequately insulated. This is one of the major weaknesses of new home and it is why you get ice damming in so many Vermont homes. It’s about air leakage, not roof venting.
8. Blower Door Tests
Be sure to have your builder perform multiple blower door tests especially BEFORE insulation and drywall. This will allow you to do detailed diagnostics and trouble shooting on your air barrier and take care of any problems. This is much harder to do after insulating. Your home should be at or under 1 ACH50 before you insulate. We typically do 3-4 tests before we are all done. This is a great tool to use and in my experience is under-utilized by most builders. We have all our own testing equipment and regularly perform the testing, rating, modeling and analysis for other builders and homeowners throughout Chittenden and Addison Counties.