Save Money by Insulating Your Home

Learn ways to save money by insulating your home, includes new insulation techniques, information on materials used for home insulation and reasons for insulating your house.
October/November 1997
http://www.motherearthnews.com/homesteading-and-livestock/save-money-by-insulating-your-home-zmaz97onzgoe.aspx
Diagram: Home insulation 1.


MOTHER EARTH NEWS STAFF

This revolution in insulation techniques will help you save money by insulating your home. 

It has long been accepted that the best way to reduce energy use is to conserve it. In America, as well as in western Europe, we use a disproportionate share of the world's energy as we rapidly diminish the fossil supply. In the northern latitudes, above 35 degrees or so, we have to supply a titanic amount of energy to heat human spaces, but in recent decades, we use a near equal amount of energy to cool these same spaces as we move south of the 35 degree latitude. One's energy bill in mid-Florida for cooling closely parallels that of someone in Wisconsin or New England for heating.

In order to substantially reduce this energy waste, we must learn to construct residential and commercial spaces that are more resistant to energy flow. The incorporation of insulation as a means to retard energy flow is a relatively recent idea that wasn't generally used until after W W II. We measure insulation in units, called R (which stands for "Resistance" to heat flow). If a substance has R value it doesn't know if its stopping cold or heat but simply that it is resisting the passage of energy through it. Crudely, one R is about equal to a 1 inch thick piece of softwood. One generally has a feeling for wood, and most everyone can envision having a piece of 1 inch pine wood on their hand with a block of ice on top (or a small fire) and realize that it would be some time before one would "feel" the heat or cold. One R is quite a lot of resistance. It is therefore easy to understand that two pieces of 1 inch pine would have twice the R-value.

Also bandied about in the insulation books is the term "U value." This latter term is a measure of overall heat transmission, which is the reciprocal of R. It is best understood by the equation 1/R = U. My apologies for bringing algebra into this discussion, but it is useful in energy calculations because "U" is the number of Btus transmitted in one hour through one square foot of insulation, assuming that there is a one degree Fahrenheit temperature difference between the outside and inside air temperatures. Now take a breath. The hard part is almost over.

It's obvious that we want to surround human spaces with a lot of R value to conserve heating and cooling energy. Real world application of this basic idea, however, is a subject that is debated and misunderstood by many people who, frankly, should know better. Naturally, the most commonly used insulation material tends to be one of the most highly advertised, aggressively marketed, and by all appearances, economical home building products in America. This material's dominance is such that you have it in mind before I even print the word—fiberglass. Though it is being replaced by a newer fiber, Miraflex, which doesn't have undue health implications, fiberglass is still the hulking presence in the marketplace.

So how do we get the most effective "R" value for our money? You have no doubt seen numerous charts listing the R values of all kinds of materials. Trouble is, the goal of achieving a good assembly is not quite as simple as picking various R's from a chart and adding them up. We must understand the interaction of the various parts, the correct assembly, their cost, and, most importantly, moisture movement. Following this reasoning leads us, surprisingly, to different methods than those which are commonly employed.

There are many materials sold to insulate spaces. One can choose cellulose, balsam wood, fiberglass, various radiant barriers, or the foam insulations (poured or air-blown into place) such as bead bond, Styrofoam, or urethane (really polyisocyanurate).

To determine a desirable insulation assembly one must think about the downfall of many installations which are actually moisture accumulators. During the heating season, the moisture movement or drive is from the inside out. Once an air conditioner is turned on, the drive reverses from out to in. The drive is simply moisture trying to equalize itself by moving from more saturated areas to less saturated ones, and water vapor is notoriously tough to contain. It is also invisible so its movement is often misunderstood and easy to ignore. Common building materials such as wood and concrete readily allow passage of water vapor through them, and the major problem with today's insulation systems is their failure to control it. In fact, in the last 15 years or so, we have done much to tighten homes on five sides of their box, but we have not done anything about the sixth side, the one under your feet. You can easily visualize the problem by placing a drinking glass outside on the ground upside down and checking it several hours later. You will observe that it is filled with moisture. Houses not sealed from the ground are likewise always taking in moisture, the root cause of many problems often blamed on the walls and roof. The typical "musty concrete" smell common in basements is evidence of this.

And if Home Insulation isn't Enough of a Problem?

There are two schools of thought as to how best to button up a home against heat/cooling loss and moisture penetration. The first employs urethane which is installed outside of the house frame and which acts as a cocoon. The second is probably surrounding you at this moment—the traditional system employing material installed in interior spaces. This system has a vapor barrier on the inside with the frame spaces filled with fiberglass combined with the inside and outside finishes. Roofs done in this manner usually have venting at the eaves and peak to allow excess moisture to escape. Sounds great, right? Hold onto yourself, because innumerable problems occur with these roof insulation assemblies, ranging from simple incorrect installation to the extreme of snow blocking the ridge vent, stopping most air and moisture movement. The resulting rapid build-up of moisture further degrades the insulation causing ice damming and even water damage (often misidentified as a leak). This insulation failure has been present for decades in many up-country open ceiling buildings.

Several considerations to note here are that moisture movement and air movement are not connected although air movement can influence moisture movement. Next, consider that the real value of fiberglass insulation is the trapped and dry air it should contain. Most fiberglass installations do not allow the air to be trapped or dry-and therein is the problem.

If you look at Diagram A, depicting the most typical wall and ceiling fiberglass insulation assemblies that meet codes requiring R20 in walls and R30 in the roof, you will note a significant problem. Regardless of how we configure our installation, the dew point at freezing (and, in fact, across a whole range of standard performance temperatures) is always within the fiberglass. This accumulation of moisture as frost or droplets can degrade the R values by 30%-60% at midwinter or well into the air-conditioning season. The most commonly installed inside vapor barrier, which is polyethylene sheeting, is pierced by hundreds of nails and penetrations with many lineal feet of edges which are not sealed very well in its standard configuration. We also note that roof fiberglass installations encourage air flow through them, making it hard to achieve trapped, dry air there. During air conditioning weather, moisture readily invades the space from outside where there normally isn't any vapor barrier.

A superior approach is Diagram B, where we substitute a moisture-proof urethane, as a vapor barrier, everywhere on the outside of the frame. The ideal material is polyisocyanurate (which, to be efficient, must be sealed very carefully at all joints and penetrations) which allows the freezing point to fall within the urethane. Since water vapor can't enter polyisocyanurate's cellular structure, we have a desirable condition where the freezing dew point never occurs, and it is also eliminated across most of the range of standard performance temperatures. Another important point is that the proper polyisocyanurate insulation is dimensionally stable, as it has real foil facers and an internal glass-fiber matt, so the joints remain tighter across the wide range of temperatures the building shell is exposed to. Note that it takes a minimum of 2 inches of urethane to achieve this in climates colder than 5000 degree-days with Diagram B, using 0 degrees Fahrenheit as the cold point. The best way to retrofit existing buildings in this way is to remove the siding and to apply a minimum of 2 inches of tightly sealed polyisocyanurate completely outside the frame. Then install minimally nailed battens to which new siding is attached. This retrofit job should include carefully sealing all new windows and doors with high quality caulk. This will immediately cut your energy bill in half.

It's possible to achieve an even better result, one in which the dew point is within the foam cellular structure during 95% of temperature conditions. Diagram C depicts 4 inches of foam installed in two 2 inch staggered layers to achieve an overlap of the foil-faced joints. These joints must also be taped with a quality foil tape.

To achieve the goal of keeping moisture from penetrating the entire structure (remember, we want to keep it inside in winter and outside in summer), we must surround (or cocoon) the structure on all six sides including underneath. The next step is to choose doors and windows that least penetrate the urethane envelope. This eliminates wood as a material, so we must use modern, commonly available steel or fiberglass-surfaced urethane core doors (with quality seals) and windows that are completely resistant to moisture movement. Windows in which the wooden sash is totally encased in vinyl are very good as well, and fiberglass frame units or vinyl construction will also make the grade, but, overall, comparable unit R values, long term warranty, and quality should be high on the list when you make your choice.

Once your home is buttoned, how can the seal be maintained over your lifetime . . . and your children's? Well, I needn't tell you about keeping windows and doors shut, but there are other unexpected "hole pokers" at work that you might not be aware of. The common practices followed by many sincere, well-meaning contractors and their various subs will led them to poke holes in your cocoon without proper sealing or caulking. The telephone or cable guy will inevitably drill a large hole for a small wire and not seal it. Just use a one-component urethane caulk and follow the guy around. Who knows? He may even be miffed enough to grab the caulk gun and do it himself.

If there is a void in the insulation or a substantial air leak around a window, door, or vent, you'll soon have a problem. The first, as you might imagine, will be a reduced R value at any leak, leading to moisture accumulation . . . which leads to rotting as the moisture always "sees" internal wood . . . which leads to carpenter ants and other problems. So we can't have any voids in the system. This is easier said than done, but a little diligence will save the day every time.

The goal is to have an insulation assembly (urethane plus structure plus inside and outside finishes) that approaches a performance of R40. This is drastically different from claimed R values of various conventional systems, systems which don't control moisture and air infiltration, and that perform at levels 30%-60% less in mid-winter or during the summer's air conditioning season. Having had experience with hundreds of homes tightly wrapped everywhere with 4 inches of urethane, I can attest to many positive benefits not normally realized. Some are obvious:

Save Money by Insulating Your Home

• It drastically reduces heating and cooling costs and allows a small heating system to easily keep even temperatures. The real aluminum foil surface (not an imitation plastic and paper surface covering) of the urethane gives an excellent radiant capability inside the structure from its reflective value. It is possible for such a system to be used in passive solar structures—and it will keep the house from freezing even if left with no other back-up heating system, in regions that require 10,000 degree-days!

• It is a wonderful sound barrier, shutting off the din of the busy world outside. Most noise comes through the windows and doors.

• It allows moisture levels inside in winter to remain at 45%-50% relative humidity, simply as a by product of our washing, breathing, cooking, etc. This is true for interior volumes up to about 25,000 cubic feet with a family of four. In summer heat waves with outside humidity at 80%-90%, we can maintain inside humidities of 50%-55%. Other houses without the envelope are sieves to moisture movement, and the homes rapidly loose moisture content in early fall and gain it all summer.

Air conditioning loads are less (but we should really call AC dehumidifying as that's really what it does) because humidity levels can be maintained at 55% or less even during the most humid days.

• Performance R40 roofs don't have ice damming or icicles. In fact, the snow stays on the roof, and snow adds an additional R8 for each 12 inches of snow. In addition to the added insulation value, you'll be able to cash-in on a bonus: the temperature of the snow 12 inches down at the roof surface is 30°F, rather than the 5 degrees Fahrenheit to 15 degrees Fahrenheit temperature of the average winter day. This may require a stronger roof to support the snow load. Such a plan can be worth several million free Btus, depending upon the size of your roof. NOTE: All those roofs out there with claimed R values at or near R40 that still have icicles and ice damming are betraying a system that simply doesn't work.

• We have the savings in energy from not loosing water vapor through our envelope which can range from several quarts to a gallon per day. It takes 970 Btus to evaporate 1 pound of water so 1 gallon saved is over 8000 Btus.

• The urethane system does not overly construct airflow in residences (commercial installations need different considerations). If we exclude internal sources of combustion (no furnaces) and exclude unvented gas appliances, we can live very comfortably in these spaces. An occasional wood or pellet fire in an air tight stove is fine, and a window open once in a while for ventilation is a luxury we can afford with new found efficiency.

• It Works! These R40 structures built as homes without furnaces save an average $1,800 of fossil fuel per year. More importantly, they do not each dump 12 tons of C02 into the downwind atmosphere.