Affordable Energy Efficient (Green) Housing
An energy efficient house at an affordable price – what a dream! In the real world, perfection is probably not possible, but there are measures that we can take to make homes more cost and energy efficient without breaking the bank.
Taking time to plan up front not only makes a job go more smoothly, but also avoids expensive retrofitting. It also permits the project planners the opportunity to easily introduce energy efficient improvements into the plan.
It starts with design. During this phase, all critical team members meet to ensure that the building envelope, water management systems, and mechanical systems are specified, materials priced out, and integration planned properly. By the end of the design phase, everyone involved knows exactly where all the ducts, wires, plumbing pipes, insulation, air barrier, and flashing details are going to go, what materials they'll use, and when their part of the project will begin and end.
A complete HVAC design should be conducted. Before the foundation is built, the HVAC (heating, ventilation, and air conditioning)contractor should understand the heating and cooling loads, which system is going in, and all of the distribution details.
Some rules of thumb:
- 1000 square feet per ton of air conditioning capacity.
- All distribution inside the envelope. Do not place ducts outside the envelope, such as in attics and crawl spaces, which can become encapsulated.
- Do not use atmospheric combustion systems, which means either electric (for example, heat pumps) or sealed combustion.
Along with the HVAC design, a HERS rater works up the preliminary HERS rating. ( http://www.resnet.us/hers-index) The Home Energy Rating System (HERS) Index is the industry standard by which a home's energy efficiency is measured. It’s also the nationally recognized system for inspecting and calculating a home's energy performance. By taking this step, the project team creates a baseline for evaluating energy saving strategies that are proposed. The U.S. Department of Energy has determined that a typical resale home scores 130 on the HERS Index while a standard new home is awarded a rating of 100, meaning that a new home is usually 30% more energy efficient than an older home.
The building site should be evaluated so that the building can be oriented properly to allow for efficient passive heating and cooling. Erosion patterns and tree protection should be considered as well.
Most energy efficient builders agree that the insulation levels specified in the 2012 IECC are the standard to measure up to. The building envelope must be complete and continuous and the insulation and air barrier must be in contact with each other and use materials that will stay in contact with each other for the life of the assemblies. Grade I insulation is a must. Thermal imaging will reveal insulation holes, and the Blower Door test will measure the “tightness” of the building. (See this great article by Joseph Lstiburek on measuring building “tightness,” “Just Right and Airtight.”
Taking these measures during a home construction project can result in more energy efficiency for the buck, and help us take care of our planet.