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"CONSERVATION IS STILL THE KEY FACTOR in your energy bills!!"

Contrary to what many log companies might say, there is no mystery at all about the science of energy in log wall R-values. The greater mystery is in the general understanding of the delivered R-Value vs rated R-Value of fibred insulations in walls in actual use, often estimated at less the half the rated R-Value of the fibred insulation. R-Values for logwalls are based very simply on the R-Value of the wood and its thickness. The R-Value is the inverse of the U-Value. U-Value is expressed as Btu's per square foot of heat lost over time. We should basically evaluate logwalls the same as you would rate any other conventional material heat loss. Your local building engineers have ready access to the R or U-Values of various species of wood. Simply get the R-Value of the wood by species, compute the average thickness of the wall, and analyze it as you would any other structure. Because the performance of wood as an insulator is hardly affected by changes in humidity or temperature, logwalls tend to deliver a very high percentage of thier rated R-Value in actual use, unlike typical framed walls with fibreglas insulation. Air infiltration on modern log homes has been improved to equal or surpass the air-tightness of modern frame construction.

Here in the United States, our building codes' energy regulations are mostly in accordance with the ASHRAE (American Society of Heating, Refrigeration, and Air-conditioning Engineers) standards. ASHRAE standards are incorporated by reference into the national building codes. ASHRAE did a study about thermal mass in building materials such as concrete block walls, various masonry constructions, and solid timber walls (such as actual full logs or D-shaped milled random length lumber walls.) From the studies, ASHRAE derived and included in a handbook called "The Model Energy Code", a formula to be used to adjust the actual wall's R-Value to reflect any gain in performance from thermal mass.

The ASHRAE thermal mass calculations in the model energy code use the local degree days and other data to help determine the performance of a thermal mass wall, and for example, in Missouri, or Tennessee, the additional R-Value created by thermal mass construction of 6" or greater thickness wood of any species, is about 1.2 additional R-Value per WALL, (as in: 7" average thickness yellow pine wall @ r-1 per inch of thickness = R7 plus R-1.2 for thermal mass=total R-Value of R-8.2. And as one moves northward into more severe heating requirements, such as say, Minnesota, the additional R-Value due to thermal mass quickly falls to nearly ZERO. Do not fall for any hype about thermal mass in your climate. A key fact to remember would be that the thermal mass effect is a heat storage battery, and like any battery, the energy within it had to come from somewhere, likely your furnace or stove.

Just buy the biggest fattest logs that you can afford. For most softwoods, expect about 1.25 R per inch of thickness. and then use a very high R-Values and low air leakage in the roof system. Big logs have less lateral joints and if well built, provide for very airtight structures. Log walls will work well in your area, but you need all the R-Value you can get. High Thermal Mass Homes, including Log Homes, can be among the top performers in heating and cooling efficiencies and in perceived comfort. When I said don't listen to Hype about thermal mass in your climate region, I was referring to claims of high "equivalent" R values. Think of Thermal mass like a rechargeable battery. Like a battery, it can give you no more energy than you put into it. In spite of the fact that it can contain a sizable number of BTU's due to the high specific heat content of wood, the presence of thermal mass does not negate the fact that the heat movement through the wall continues inexorably as determined by the temperature differences beside the walls and the R-Value of the walls. What thermal mass can do in one climate is not the same as in another climate. For example, remember that without summer air conditioning, homes are often cooled by nocturnal or night-time cooling. Conversely, during the winter, we can design and use the building and its contents to capture heat from the sun.

During the hot seasons of my youth, long before the air conditioner on the farm, my grandma or mother would open all of the windows and doors as soon as the temperature was cooler outside than inside the house, maybe even sooner if the breezes were favorable. And just after dawn, they'd make us all close up the house tightly and conserve all that cool air. The house and contents (thermal mass) would have cooled off as well during the night (emptying the battery), and, like a weak battery, be ready to absorb energy from the warm air during the day thereby helping the house to stay cool through much of the day. The house and contents would gradually heat up during the day (charging the thermal mass "battery"). This cycle of cooling at night & heating at day (discharge, charge) would repeat as long as the season lasted. My mother would swat the behind of any miscreant who wasted cool air by forgetting to close a window, or by holding a door open too long, or even going in & out too many times! She knew to conserve the cooling provided by the dark nights.

Modern solar building practices which can be applied to most home designs, reverse that process for heating by allowing thermal mass to charge with the sun's energy during the day. Then the stored energy inside the mass of the home is naturally released into the home as it cools. Log Homes, like other high mass homes can store enough energy (whether you "charged" the mass with electric heat or solar) to keep the temperature of a house stable through fluctuations in heating or cooling needs. Logs happen to be of much higher R Value than other high mass walls, and can form a simple wall system which has two abilities, insulation, and relatively high thermal mass.
Now a significant point here is that to keep a home warm in a very cold climate or cool in a very hot climate, conservation is still the key factor. Solar might warm your bones through radiation, but the sun will never warm up all that thermal mass if you and your building don't conserve those BTU's! No amount of thermal mass will assure an effective solar heating strategy without very good insulation. Virtually all milled timber walls and full log walls provide more than adequate thermal mass. But wall thickness and the R-Value of the wood are much more important. If you build a log home you will have much more thermal mass than stick-built. But look for wall R values in severe climates greater than R12 MINIMUM. If you don't, you will need to over-compensate somewhere, by adding more insulation to other parts of the home, and larger heating bills, and less windows and additional solar glazing, etc. Put another way, for comfort & energy bills, would you rather have 18" thick masonry wall with a very high thermal mass, and very low R value, or an 6" R-18 stick-built wall? Given the choice of one or the other, most people would rightly opt for the stick-built.

When using Log walls, don't settle for high mass and low R values. In Northern climates, acceptable wall values (empirically speaking) are R-18 and greater. For example; using lighter woods, (which tend to have higher R values than heavier, denser species,) such as Western Red Cedar or Engelmann Spruce with R=1.25 to 1.5 per inch; in a mean diameter 16" log wall; with an average thickness of 12"; can have an R value of about R18. Then add at least an R-40 roof and gable system to the picture. Build it tightly. Use high quality windows and not too many of them; and you will get high performance from your building shell. Then site the building carefully with regard to wind and sun, and the natural insulative value and thermal mass in your log walls will contribute immediately to your comfort, and, if you can "charge your batteries" with free solar heating or cooling, the logs will use the thermal mass to contribute very real savings to your energy bills. Optimize glass exposure, 8-12% of floor area in most US climates would be ok, not much if any more. and get the highest R value (go by UNIT value, not center of glass ratings) that is available.