Heat Loss and R-Value
Heat moves through a building by 3 methods:
Conduction
Heat that moves through materials such as insulation or metal studs. This is the measure of 'R-value', the ability of a material to resist heat flow. Glass and steel have a very low R-value, while insulation has a much higher value. The higher the R-value, the longer it takes for energy to move from one area to another. R-value is an important consideration, but is not the whole story. The R-value of a material is measured in a vacuum, hardly a real-world scenario.
Convection
The Department of Energy states that 40% of heat gain/loss in a building is due to air leakage. Air currents strip energy from a building as they move through it. Good air-sealing using foam insulation and caulking is essential to building performance. Ventilation is good, but we want to control where it occurs.
Radiant Energy
This is the energy that you feel emanating from a South-facing brick wall after the sun has gone down. Heat also moves as electromagnetic waves, and can be reflected by a mirror much the same as visible light. It is this infra-red radiation that allows us to take pictures of heat loss with thermal cameras.
For a time in the 50’s and 60’s, it was thought that if we could reflect this energy back with mirrored wall, our home’s energy loss would be minimized. This worked in the vacuum of space, but in the real world conduction and convection have a much bigger impact on a homes energy performance. Radiant energy loss is a factor, but far less than the first two types of energy loss.
Quality in Building Envelopes
Insulation is made to address R-value, but it should also factor in air movement as well. Insulations such as standard fiberglass and tri-polymer foam are not effective in stopping the movement of air through the framing members of buildings.
Moisture permeability is also a key consideration for insulation materials in a building envelope. How does the material react to water intrusion, moisture laden air and changes in temperature? Does the material allow moist air to collect in the wall or ceiling assembly? Does moist air have a tendency to turn to water and create mold or other problems?
Energy-efficient buildings are achieved through a combination of excellent air sealing and good R-value. Cellulose and acrylic-based fiberglass can be effective in tandem with an excellent caulking package. Polyurethane spray foam can address both issues with one product, however. There are different types of polyurethane spray foam for different applications.
Although we also caulk our open-cell spray foam building frames for truly superior performance, foam insulation has some significant advantages in many buildings. Because it is adhesive, it sticks to and encapsulates framing members. We can spray onto open rafters and other areas whereas other types of insulation would succumb to gravity over time.
By bringing attic areas into the conditioned envelope with open-cell spray foam, a builder can also install ducts into this space for easier HVAC retrofits. Open-cell spray foam also is flexible and forgiving with water intrusion. Due to it’s cellular structure, it allows liquid water to permeate it without absorption, while inhibiting the movement of water vapor.
“Decoupling” the building framing members can also yield good results. Framing members can act as thermal bridges, syphoning energy from a building. With infra-red imaging, we can detect each and every framing member that connects the inside to the outside due to on-going energy loss. A builder can greatly reduce heat transfer by installing an air space and/or an insulation product over framing members. Conductive heat flow is interrupted with these techniques.
Insulation materials can also be sound attenuators, particularly in tandem with decoupling the framing. Noise between rooms and from outside can be mitigated with insulation. Sanitary lines between floors are another area where sound attenuation can improve the quality of life. Spray foam insulation is one of the most effective methods to deaden sound transmission.
Insualtion Materials
Choosing the right insulation product for your project can have a large impact on your home or building's energy efficiency, comfort, and indoor air quality.
Open Cell Spray Foam
Open-cell spray foam is one of the best all-purpose home insulation materials. It is a lightweight semi-rigid polyurethane foam insulation product that has roughly the consistency of a nerf ball or a seat cushion, although it will compress permanently under pressure. Its open cell structure will allow liquid water to pass through without absorption but resists the flow of air, and with that water vapor.
Open cell foam is also called lightweight foam or 1/2-pound density foam. The main advantage of open cell foam is that it provides an excellent air barrier and and sticks to places other insulations cannot. Excellent sound attenuation properties also add it it’s advantages.
Closed-cell Spray Foam
Closed cell spray foam is a heavier rigid polyurethane foam insulation that provides a higher R value and a complete air and moisture barrier. The material is also called rigid, or 2-lb density foam. This product is typically best for exterior applications, below slabs and on masonry foundations, or in interior applications like pool rooms where moisture drive may be an issue. It’s properties as a moisture barrier helps resist the intrusion of water, and it’s rigidity can also be a benefit. It should be noted that we do not recommend the application of closed-cell foam to wood members. It is inflexible and may separate from wood that is moving, and also will not allow moisture intrusion in wood framing to be detected before significant damage occurs.
Open Cell Pour Fill
For wall retrofit situations, we use an open cell spray foam product that is specifically designed to rise slowly and fill empty ballon frame walls. This material is by far the best material for filling walls, and the drawback is that the work requires a good deal of skill and complete access to the wall areas that we are working on.
Cellulose
Cellulose insulation is a fiberous material that is made from shredded newspaper, borates, and glue. The material can be a good solution for pour on a ceiling to insulate a large area economically. With enough depth it does provide a pretty good air barrier, but it is still a fiberous material that is subject to settling or shifting. Some applicators also mix cellulose with water and apply the material vertically in stud cavities. We do offer cellulose work, especially in retrofit situations where there is already material in an attic, but we think that foam is better in many appliications.
Fiberglass
Fiberglass is a fiberous material made of woven strands of glass. This material is obviously the main material used for insulation - and has made a significant contribution to energy efficiency, mainly because it is very inexpensive and is better than nothing. (somewhat better). We believe that there is enough fiberglass in the world, and do not offer this product.
Cementous Foams
There are several brands of shaving cream type foams that are used for wall injection and block fill. These foams are great because they are relatively inexpensive and you can push them relatively well into an existing cavity. We have partners that do this work, but don't currently offer this product. When installing this product you have to be carefulll because the material is water based, and is prone to shrinkage or collapse as it dries.
Mineral Wool
Mineral wool is made from woven gypsum fibers. It is a good insulator and an excellent fire retarder.
Cotton Bats
There are several brands of recycled denim bats on the market that are a good substitute for fiberglass. They are neat because they use recycled cloth as an input, and they have very good sound attenuation properties. They contain the same borate materials as cellulose to improve fire properties and inhibit mold growth. We like this material, but prefer foam materials that can provide better air sealing properties
Structurally Insulated Panels
Structually Insulated Panels, or SIPS, are made of a sandwich of plywood and polystyrene foam. This is an excellent approach for new construction, since it provides a great air barrier and thermal barrier. The key with SIPs is to make sure that the seams are well constructed so that they don't shift.
Insulated Concrete Forms
Insulated Concrete Forms, or ICF is a very solid way to build a foundation wall, or an entire exterior wall. It is made with a sandwich of polystyrene with concrete poured on the inside. This provides an excellent mass wall with great insulating and structural properties. Unfortunately you don't get the benefit of the thermal mass on the inside because of the polystyrene sandwich.