A superinsulated (SI) home can save 75% of the annual energy costs for heating and cooling compared to a standard home, and is also more comfortable and healthy for the occupants. SI houses can be of any design—Colonial, Victorian, Contemporary, Ranch, etc.—and often look identical to a conventional home, especially from the exterior.
The design and construction of a conventional house will vary according to the area of the country, and the climate, in which it is built. The same is true for a SI house. A superinsulated house built in Florida, where there is a 'cooling climate' requiring cooling most of the year, will be very different in construction from an SI house built in the northeast, which has a 'heating climate'. This article will focus on residential construction in the northeast.
Flexibility is a key trait of SI homes. They can be built on any building lot, facing any direction. If a building lot has an unobstructed southern exposure, it is recommended that the house be oriented to take advantage of the solar gain, but this is not required.
Elements of Superinsulated Houses.
All superinsulated houses share three important elements:
* They are constructed to be air tight.
* Compared to conventional houses, they have a higher level of insulation, hence the name 'superinsulated'.
* They have a ventilation system to control air quality.
All three of these elements are planned into the SI house during the design stage.
Although SI homes resemble conventional ones in appearance, there are numerous, subtle differences. SI houses are constructed using conventional building materials for the most part, but these are assembled somewhat differently, using more care and attention to detail during certain stages of construction. For example, very important air tightening procedures are commonly preformed integral with the framing of the house. In fact, all construction on a SI house, from the beginning to the end, is performed with the simultaneous installation of preplanned air tightening, insulation, and ventilation systems in mind. This requires careful education, communication, coordination, and supervision of subcontractors.
There are many different methods for building a SI house including: double wall, strapped wall, stress skin panel, air-tight drywall approach, 2x6 with foam inside, 2x6 with foam outside, strawbale, and others. Builders generally select the method they feel most comfortable with depending on their experience and the skill level of their crew and/or subcontractors.
Although SI construction may seem complicated, any skilled, veteran, professional builder with a commitment to quality and close attention to detail can successfully build a SI house. Contractors who build quality conventional houses already have 90% of the skills they need to master SI construction.
Any existing house can be retrofitted to be superinsulated; many have been done and many more will be. This being said, it is easier and more cost effective to build a SI house from the ground up. Many of the components and systems (notably the air sealing and insulation systems) are integrated within the exterior walls of the SI house, and usually require extensive and costly renovation to retrofit.
The ventilation system is a critical component of a SI house. It purges stale air and indoor air pollutants. It introduces the correct amount of fresh air for proper air quality into the house and distributes it evenly throughout the living space. The importance of a properly designed and installed ventilation system for a SI house cannot be overemphasized.
Stale air is typically exhausted from the kitchen and the bathrooms, since these areas have a high concentration of moisture. Moisture is a primary indoor air pollutant, and frequently needs to be removed. Other pollutants, such as carbon dioxide, cooking odors, and smoke, also need to be purged, but moisture remains a key 'indicator' pollutant. When water is seen to condense on cold surfaces such as window panes, the relative humidity is too high in the house and the rate of ventilation (measured in whole house air changes per hour or ACH) must be increased. As a rule of thumb, for proper air quality, most SI houses require 1/3 ACH, or 10-20 CFM (cubic feet per minute) per person when occupied.
Ventilation systems fall into two types: heat recovery and non heat recovery. The Heat Recovery Ventilator or HRV is the most common of the recovery machines. A HRV is a machine which takes warm, stale air out of the house and brings cold fresh air in. The HRV runs both air flows through a heat exchanger, using the heat from the outgoing stale air to preheat the incoming fresh air. Ducts then carry the fresh air throughout the house. There are a number of manufacturers and several different types of HRVs.
A new type of HRV becoming popular is the ERV or Energy Recovery Ventilator, which recovers moisture as well as heat. The ERV is helpful to control the indoor relative humidity; a level of roughly 35% is recommended.
The most common of the non-heat recovery ventilation systems are the Exhaust Only systems. With these systems, only the exhaust air is fan forced and runs in ducts. An exhaust only ventilation system can be as simple as running kitchen and bath fans continuously when the house is occupied. A high-tech hole in the wall (with a diffuser to mix the incoming air and prevent drafts) is provided for each room of the living areas to let in a continuous trickle of fresh air.
Safety is an important attribute of the SI house. SI homes always use sealed combustion heating units when fossil fuel furnaces, boilers, or domestic hot water tanks are specified. Sealed combustion heating equipment does not use any inside house air for its operation. It takes its combustion air directly from outside of the house, and it blows its exhaust gases directly back outside. Since there is no contact between combustion gases and house air in a sealed combustion heating unit, backdrafting of flue gases (carbon monoxide) is impossible.
Any fireplace or wood stove in a SI house must have a duct to supply outside combustion air as well. In addition, dedicated make-up air should be provided for any large or powerful exhaust fan such as a kitchen rangehood. This can be accomplished by simply cracking a window in the kitchen when the rangehood is operating.
SI builders take precautions against radon, a naturally occurring radioactive soil gas, and a suspected cancer agent. If radon is present in the soil or the ground water at a site, it can enter the home through the basement. Provisions for a radon mitigation system are built into each SI house. After testing the finished home, if radon gas should pose a problem, the mitigation system can be quickly and easily hooked up.
Advantages of Superinsulated Homes
SI homes have many important advantages:
They conserve energy without impacting the occupants’ lifestyle.
They are more comfortable, with no drafts, cold spots, or temperature stratification.
They are healthier because air quality is not left to chance but is controlled and can be monitored.
There is commonly a higher relative humidity in a SI house. People who are bothered by dry house air in the winter will be more comfortable.
They are safer because backdrafting of combustion appliances is impossible.
They are quieter to outside noise because of thicker walls and better windows.
They save money, frequently 75% of heating and cooling costs.
They are more durable because of the quality of the materials used, the care in construction, and because of applied building science principles.
They are environmentally friendly, helping to build a sustainable future.
What does all this cost?
Superinsulated construction typically costs about 5-7% extra compared with conventional construction. Most of this cost is associated with better windows and doors, high-efficiency HVAC equipment, more insulation, and air sealing. A premium is almost always paid for quality, whether the product is an automobile, a consumer product, or your home.
Superinsulated building is now a force the marketplace. SI building practices are included in Canadian building codes and are standard practice in many parts of Europe. Changes to the Model Energy Code have been implemented by the US Department of Energy and US Department of Housing and Urban Development in this country. Monetary incentives, such as Energy Rated Mortgages which increase the borrowing power of buyers of energy-efficient homes, are in place at banks right now. Programs like the Energy Star Homes Program, sponsored by the Environmental Protection Agency and the Department of Energy, encourage builders to build SI homes and provide a rating system to evaluate energy performance.
Consumers interested healthy indoor environments, decreased energy costs, environmental friendly lifestyles, and quality in their homes can insure that superinsulated building becomes standard practice in the US.