Insulation & Windows

You really can't overdo insulation. It is relatively cheap compared to other components of the house and you will pay for under-insulating for the life of the house. The more extreme the temperature swings from your desired indoor temperature the more insulation you will need ... Fargo, ND for cold and Yuma AZ for heat.

R-Value: A material’s R-value is the measure of its resistance to heat flow. It is important to know the R-value because many states or regions require a minimum amount of thermal resistance for building elements. The way it works is simple: the higher the R-value, the more the material insulates.

Heat rises so you want a higher R-value in the ceiling than walls and more in the walls than the floor. We have 3 inches of foam board (R-15) in the floor, R-19 in the walls and close to R-50 in the ceilings. We put an additional inch of foam insulation under our radiant slab because we're using radiant heating system ... most experts will say that an R-10 in the floor is fine.

You can make a building extremely energy efficient if you have no windows, which are the major source of heat loss. However, few of us want to live without a view, so there must be some trade-offs. Generally, you should have no more than 20% of the floor area as windows if you wish to qualify for an Energy Star Home.

Windows typically comprise 10-25% of a home's exterior wall area, and account for 25-50% of the heating and cooling needs, depending on the climate. Thus, it is critical to consider high-performance, energy-efficient windows when constructing a new home.

We decided to go exclusively with Anderson Windows because they are the only GreenSeal window manufacturer, eg they are efficient and the manufacturing process is environmentally friendly. As a company, 98.5% of the input into the Anderson factory is converted to products ... an incredible efficiency. For remodeling Anderson has a Renewal Line which will actually take your old window and convert the glass and wood into a new renewal by Anderson window.

Windows have entirely different values than walls ... U, E, and VT ... definitions:

Low-emittance (Low-E) coating. Microscopically thin, virtually invisible, metal or metallic oxide layers deposited on a window or skylight glazing surface primarily to reduce the U-factor by suppressing radiative heat flow. A typical type of low-E coating is transparent to the solar spectrum (visible light and short-wave infrared radiation) and reflective of long-wave infrared radiation.

U-factor (U-value). A measure of the rate of non-solar heat loss or gain. It is expressed in units of Btu/hr-sq ft-°F (W/sq m-°C). Values are normally given for NFRC/ASHRAE winter conditions of 0° F (18° C) outdoor temperature, 70° F (21° C) indoor temperature, 15 mph wind, and no solar load. The U-factor may be expressed for the glass alone or the entire window, which includes the effect of the frame and the spacer materials. The lower the U-factor, the greater a window's resistance to heat flow and the better its insulating value.

Visible transmittance (VT). The percentage or fraction of the visible spectrum (380 to 720 nanometers) weighted by the sensitivity of the eye, that is transmitted through the glazing.

Solar heat gain coefficient (SHGC). The fraction of solar radiation admitted through a window or skylight, both directly transmitted, and absorbed and subsequently released inward. The solar heat gain coefficient has replaced the shading coefficient as the standard indicator of a window's shading ability. It is expressed as a number between 0 and 1. The lower a window's solar heat gain coefficient, the less solar heat it transmits, and the greater its shading ability. SHGC can be expressed in terms of the glass alone or can refer to the entire window assembly.

Before you install insulation, you need to make certain that all of the cracks are filled. All of the structural gaps with the foundation and supporting beams were caulked. In addition, all of the structural elements were caulked and the holes for plumping and wiring were filled in to reduce air flow and thus heat loss.

There are various types of insulation including fiberglass batting, blown in cellulose (the best has been treated with borate for mold control) and foam. We used Icynene which is a foam product that does not off gas and fills all the gaps in the walls.

Off gassing or smell is a central item to control in a green house. Generally, if you can smell something in the product, something rather nasty is being put into the room and thus your body such as formaldehyde ... that new car smell is not particularly healthy.

Icynene does not off gas and is stable over a long time horizon, eg it does not shrink, or settle, and resists mold growth.

The R-Value is 3.5 per inch so a 6 inch (5.5") wall will produce an insulation value of around R-19. However, because no air can travel through the insulation and it seals gaps, the effective rate is probably higher.

There is a similar product to Icynene called Biobase that is made from soybeans. However, there was not much independent testing or the product when we were making our insulation decision so we stayed with Icynene.

If you've looked at Great Products We Are not Using, there is a product called SIP (Structurally Insulated Panels). With icynene we got a comparable insulating value as a SIP panel.

Getting ready for insulation involved making certain that there are no gaps that air and cold can penetrate the house. Advanced Framing discussed elsewhere is critical, there also is a need to over insulate corners and structural beams, as we did on the outside of the walls.

Part of framing the structure includes heals over windows and doors. This allows insulation to be as complete and thick as possible on all exterior walls, roofs, and joints. The common areas that are missed with insulation are the areas behind bathroom tubs, pipe penetrations, and those narrow slits between the door jams and the wall studs. A quality builder like Polar Bear makes certain that the structure is insulated everywhere air can infiltrate to the inside living space. I

Remember a GreenBuilt Home is also Quality Built Home !!

We welcome your comments on this site.
You can email Christine Garst at cbgarst@aol.com
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Sunday December 17, 2006 05:34 PM -0800