A couple weeks ago I posted an Autodesk Academy video of my hero, Amory B. Lovins talking about integrative design. In this video Amory talks about insulating a house to the point that a heating and cooling system are no longer needed. I’d like to dive deeper into this idea. To start, let’s talk about some of the basics of insulation.
Why we insulate buildings
Here in the northern part of the country we typically think of insulation as necessary for keeping the heat in during the fall and winter (and sometimes spring) months. But the most basic purpose of insulation is to prevent the movement of heat. Both out of and into a structure. Insulation is also quite useful for keeping heat out of a building in the summer. So insulation can cut down on the need for both heating and cooling a building when more extreme temperatures hit. Having a well insulated home can reduce your energy use (and costs!) all year round.
R Values
Insulation materials are rated using an R Value. R value is a measure of resistance to heat flow, and is based on the temperature difference between indoors and outdoors, the area of the insulation, time, and heat loss. High R values provide better insulation than low R values. Now, walls and ceilings and floors are made up of multiple layers of different materials, and to find the total R value of the system, we add together the R value of each individual layer. Oak Ridge National Laboratory put together a recommended R value calculator based on zip code, heat source, and part of the building that is being insulated.
How buildings are typically insulated
If you rip open the drywall in one of your exterior walls chances are you will find fluffy, pink, fiberglass insulation. This is known as batting, or fiberglass batt insulation. Fiberglass batt has an R value of about 3 per inch of thickness.
Because heat rises, in colder climates it is important to have a well insulated roof or attic to keep that heat inside the building. Typically, houses have a blown insulation (loose insulation that is blown into a space to fill it), that can be 15 inches or more in thickness.
In warmer climates , where you want to keep the heat out of the house, sometimes the insulation batt has a shiny metallic side. This is put on the outer face of the wall to help reflect heat away from indoors.
Common Types of Insulation
There are many more types of insulation than the fiberglass batt or blown fiberglass.
Mineral Wool is a material that resembles matted wool, but is man made rather than sheep made. In batt form, its R value is equal to fiberglass batt, but as a blown insulation it has a larger insulation, making it slightly better for attic spaces.
Cellulose is a material made from plant fiber that can be used as a blown insulation. It also has a slightly higher R value than blown fiberglass. Cellulose can also be mixed with water, adhesive, and moisture retardant and used as a spray insulation, which has the advantage of being better able to get into nooks and crannies to seal up a space. Cellulose also has the benefit of being a vapor barrier, preventing the buildup of moisture, which can help prevent rot.
Foam board insulation can be made from polystyrene or polyurethane among other polys. The boards are made of dense foam that can be cut to fit into wall spaces, and provides a good amount of insulation for a small amount of thickness.
Foam spray insulation may be made from a variety of different man made materials such as polyurethane, and is sprayed into the walls and ceilings. Foam insulation is excellent at sealing up walls or ceilings that have small cracks and/or holes, however it is much more expensive than fiberglass insulation.
So, now we have a base understanding of insulation, next time we can talk about insulating for greater energy efficiency.
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Want to read more about insulation? Here are some good sources:
Energy.gov articles on Insulation
Insulation R Value Chart