Insulation and Ventilation Tips

Many new products have been developed in the insulation industry over the past few years; before discussing types of insulation, let’s take a look at some specific terms used in the heating and cooling industry.

Conduction, convection and radiation are the three most important terms to consider.

Here are the definitions per Wikipedia:

· Heat conduction, also called diffusion, is the direct microscopic exchange of kinetic energy of particles through the boundary between two systems. When an object is at a different temperature from another body or its surroundings, heat flows so that the body and the surroundings reach the same temperature at thermal equilibrium. Conduction happens in both fluids and solids.

· Heat convection only occurs in fluids. It occurs when bulk flow of a fluid (gas or liquid) carries heat along with the flow of matter in the fluid. The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is sometimes called "natural convection". All convective processes also move heat partly by diffusion, as well.

· The final major form of heat transfer is by radiation, which occurs in any transparent medium (solid or fluid) but may also even occur across vacuum (as when the Sun heats the Earth). Heat transfer by thermal radiation is the transfer of energy by transmission of electromagnetic radiation described by black body theory. (HUH!!?!)

To simplify these definitions in layman’s terms:

· Conduction is the transfer of energy through a surface, such as a window. You can put your hand near a window on a cold day and feel conduction.

· Convection is the transfer of energy through the air such as a breeze blowing through an open window or the ‘breeze’ that blows through leaky doors, windows, walls, ceilings, etc.

· Radiation is not considered as important in insulation applications but it is the energy you feel on your skin when standing in the sun.

Insulation R-values and E-values

R-value: This value was created as a standard, so one can easily distinguish between the different insulation values of products. The higher the R-value, the more efficient the product is. The most commonly used R-values are as follows:

1. R-11 – This is for a 2x4 wall and is the lowest R-value commonly used.

2. R-19 – This is for a 2x6 wall and is now the lowest allowable R-value for an exterior wall.

3. R-30 – This is the old standard for a ceiling insulation. It can be achieved with batt or blown insulation.

4. R-38 – This is the current minimum allowable value for ceiling insulation.

5. R-5 and similar values. R-5 is the value for rigid foam insulation such as Dow Blue Board in 1” thickness. We will discuss rigid foam insulation more a bit later.

6. Laminated foam insulation and Structural Insulated Panels (SIPS) come in a variety of R-values which normally exceed the minimum standards.

U-value: U-value is essentially 1 over R (1/R). This is used primarily in glass window, door and skylight evaluating and the lower the U-value, the more efficient the product is. Low E glass is a term for glass that has a lower than required U-value.

The following is a summary of insulation products, their uses and thoughts on the combinations of insulation and ventilation that are of particular importance in a quality building.

Common Types of Insulation

· Batt Insulation: Usually made of fiberglass and comes ‘faced’, a vapor barrier laminated to the side of the insulation which goes on the inside or warm side of the building. ‘Un-faced’ insulation is usually used for sound damping or when a vapor barrier is going to be manually installed on the interior of the building. My opinion is that the un-faced batt insulation, installed with the continuous vapor barrier, is superior because of the reduced air penetration due to convection.

o The most common Batt Insulations are R-11; R-19; R-30 and R-38.

o The ‘faced’ batts are usually laminated to kraft paper or foil paper. Foil paper is supposed to reflect the heat (or cooling) back into the building.

· Blown Insulation:

o Attics: Attics have been blow with various types of insulation for over 50 years. The most common product is cellulose, which is made from newspapers. Fiberglass has also been used extensively and a product called rock wool was very popular for a while. I have seen ‘unknown substances’ in attics, some of which were tested because they looked like asbestos, but in this case they were not. I personally think cellulose is the superior product, mainly because it isn’t such a skin irritant like some of the others. 8” of blown cellulose insulation equals an R-30 insulation value, and 10 1/2” equals the newest minimum of R-38.

§ NOTE: vapor barriers are not placed on ceilings because they cause the moisture that normally migrates upward in a building to be trapped above the ceiling drywall. This is known to damage the drywall and prevent the moisture from escaping to the attic which is often ventilated to allow it to disburse. (more on ventilation later)

o Wall Cavities: Wall cavities are often insulated with a method known as ‘net and blow’. This is a technique where a mesh material is stapled to the studs on the interior of the building and either cellulose or fiberglass is blown in. In a 2x6 wall, net and blow fiberglass has an R-value of 23. Similarly cellulose has an R-value of 20.

· Foam Insulation:

o Straw Foam Sealant – This is an expanding foam used to fill larger voids and usually comes with a straw attached for application. There are varying degrees of expansion and these foams should not be used around windows and doors because they can ‘bow’ the frames, causing problems.

o Window and door sealant – a similar product with minimal expansion that will not damage doors or windows.

o Polyicynene – open cell foam insulation - R-3.5 per inch of thickness

o Polyurethane – closed cell foam insulation – R-6.9 per inch of thickness

Applications, Pros and Cons of Various Types of Insulation

· ‘Standard’ Insulation: I use this term to describe the types of insulation that have been the standard in the industry for many years. This includes batt and blown insulation as described above.

o Pros – this is the least expensive method of insulating and meets most municipalities energy requirements.

o Cons – This insulation is prone to air infiltration (convection) and it is subject to the quality of the installation. For example: if you install batt insulation in the wall cavities, but don’t foam or carefully seal around electrical boxes, you will have an air leak (convection) and a cold spot (conduction). When using standard insulation, it is important to include foam sealant, which is often an option, to seal around all penetrations. This will give the most suitable application.

· Foam Insulation: this includes the polyicynene and polyurethane insulations listed above.

o Pros – these products seal all the wall cavities extremely well and provide the best R-value per inch of depth. They virtually eliminate convection and provide the lowest possible conduction. When a 2x6 wall is filled with polyurethane foam, it will have around an R-38 as compared to R-19 in batt insulation. For a remodel, where it is necessary to leave an existing 2x4 wall, filling with polyurethane foam, will provide and R-21, which exceeds required energy codes while batt insulation at R-11 does not. A fully and properly foamed home is draft free and heats and cools at the lowest cost. These homes are sometimes called ‘super-insulated’.

o Cons – Foam insulation is very expensive. Although it is not easy to determine the true percentage, it is probably 5 times the cost of standard insulation. The payback for using it may not be worth the cost although some people feel it is worth it. These products should be installed by a professional. There are ‘do-it-yourself’ foam kits available but they tend to be expensive and there are some hazards to the installer that professionals are equipped for. There are some concerns that these products may make a home too ‘tight’ and that they may cause health hazards. If a home is considered too “tight”, additional mechanical ventilation may be required. They are fully approved by the controlling agencies so I don’t feel this is a serious problem.

· Combination of Insulation Products: By using a combination of foam insulation and net and blow insulation, I believe a home can have the comfort and value of the ‘super-insulated’ home at a price that is reasonable. I refer to these homes as ‘high-insulated’ and although I have built with all three types, this is the one I recommend for the average home. It is achieved as follows:

o Wall cavities: Using Polyurethane insulation, we fill the exterior of the cavity with one inch. This seals the wall to the studs and seals around all penetrations, thus stopping 99% of convection and puts a solid barrier for conduction on the exterior of the wall assembly. We then use the ‘net and blow’ method to fill the remainder of the cavity with fiberglass insulation. This results in about an R-25 in a 2x6 wall for the insulation and I have had positive feedback from clients who have used it.

o Ceiling/Attic cavities: Once again, we install one inch of polyurethane foam directly to the top of the drywall ceiling. We then blow in 10 1/2” of cellulose insulation. This results in an R-45 value and cuts loss through the ceiling considerably over conventional blown insulation.

Ventilation and Insulation:

Most attics are ventilated. Ventilation is achieved by vents in the soffit of the home to let air in and vents on the roof to let air out. The purpose of the ventilation is to let air move through the ‘cold’ part of the attic and remove any moisture that infiltrates the attic through the ceiling. Vapor barriers are not used on ceilings because it is important for it to pass through the ceiling. Otherwise the ceiling material will collect the moisture and eventually accumulate mold and rot. A vaulted ceiling should also have ventilation and this is achieved in the same manner except air channels are usually installed above the insulation. The reason for this is that without the air channels the moisture from the house will penetrate the roof deck. Since the top of the roof deck is sealed, it will eventually mold and rot.

Fully Foamed Roof Decks:

I recently read a syndicated article from the Boston Globe, where the writer extolled the benefits of fully foaming roof rafters. He stated that using this method eliminated the need for ventilation. I disagree for the most part (with a few exceptions). In an area of high humidity, like Boston (or anywhere else), I don’t think this is a wise decision. The reason is that the moisture must go somewhere and even with a high density foam there will be tiny areas where it is not fully adhered or areas where there are pinhole sized openings in the insulation. The moisture will find and pass through these areas and wet the bottom of the roof deck, again, causing mold and eventually rot.

The exceptions: in dry climates like Colorado, it is acceptable to use foam insulation because the moisture content is so low that it will dissipate through other areas and is unlikely to cause mold or rot in the roof deck.

This is only true in lower elevations, however, because the temperature difference at high elevations is such that the warm moisture moves toward the cold air at a much higher rate and can cause the mold and rot problems. This is especially true of homes with humidifiers and even at lower elevations high settings on humidifiers can cause problems. I have read articles on this and discussed it with a roof expert and realize there are differing viewpoints, but based on what I have learned, this is my opinion. I have used this type of insulation in areas where there are no good alternatives, such as a remodel that has 2x4 or 2x6 roof joists. I first checked the heating systems and determined that there was relatively low humidity.

Summary

Insulation and ventilation should be carefully considered when planning a remodel, addition or a new home. The proper combination of these elements will make a home cost effective and energy efficient, thus comfortable. At Far Star Inc, we analyze the needs of the client and the conditions of the product to be built to determine the best combination to use.

I hope this information has been informative and useful!

Please feel free to contact us if you would like an analysis of your existing or conceptual project. We specialize in taking projects from conception to completion!

Good Building!

Steve Crook