Moose Mountain Log Homes Inc.
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Building a Super Energy
Efficient Log Home.
There are three factors to consider when you think of building a super energy efficient log home, conservation, storage and design.
Conservation can largely be summed up as the “R” factor and how well sealed your log home is.
a) In all forms of construction insulation slows the flow of heat out or coming into the building depending on the season. Insulation and vapor barrier are critical in a log home but unlike regular conventionally built homes there is an additional major factor that will significantly affect your heating and cooling bills that is unique to massive log, log homes. Insulation is important in many areas of the home. Obviously the roof, walls, plus windows and doors are key areas. Other areas, often over-looked are under the basement floor and the inside and outside of the basement walls. Here the steady conduction of heat out of the house is only a benefit in the hot summer time. That conduction of heat is never ending, as the mass of the earth will continuously absorb any difference of temperature from your home that is higher (or lower) than that of the earth temperature touching your foundation. In your windows the airspace between the panes is insulation. In colder climates consider using triple pane windows with a titanium or the low “E” film on the glass and argon gas in-between the glazing. My suggestion is definitely use the extra benefit of a titanium or low “E” and argon on all windows facing from East onward to North and continuing further around to the Northwest sides of your home (in the northern hemisphere). I would like to expand on this further in the design section. Logs can be a good insulator alone but only if there is enough log to generate a high enough “R” value. While there are many numbers floating around about the “R” value of wood, a realistic number for most softwoods is around R 1.5 per inch of wood, the denser the wood such as Fir and hardwoods the lower the "R" value and the softer and lighter the wood the higher the "R" value such as Balsa and Cedar.
b) More importantly in the energy conservation category with logs is the seal between the logs, as well as every other point in your home. Wood on wood can create a minimal seal but that is not adequate in a super energy efficient log home. Experience says a proper seal in a log wall requires two flexible internal gaskets, capable of movement with the logs but alone, under compression, needs to be an air and weather tight seal between the logs. These gaskets should be internal, inside the joinery at the closest points to the inside and outside of the log wall, with insulation between. It is hard to believe there are still builders that consider a wood on wood seal adequate and only use Fiberglas insulation between the logs with today’s energy concerns. I believe those who want to build an exceptional log home will be thankful, that the newest version of the building codes coming out now, will eliminate that approach to log construction completely. For many builders, potential buyers and owners of homes under construction a point often over looked is checking, the horizontal drying cracks that form in almost all pieces of wood. Any check that will allow air to follow the check from inside to outside of the home is a source of heat loss, often a major source. Add several of these together and you could just as easily leave a window open all winter long. I prefer to control checking prior to its occurrence than have to try and deal with it after it has already formed. A perfectly connected vapor barrier from your logs along the inside of all exterior framing, around windows and doors and along the inside of your roof can easily impact the energy consumption of your home as much as the insulation itself. Most forms of insulation have negligible values if they are damp, as water is an excellent conductor of heat. During colder weather, warm moist air migrating past the vapor barrier, through insulation in frame wall areas and ceilings will eventually reach the dew point, condensing and releasing water while it is still within the insulation, on its path out of your home. Extra effort spent on a continuous vapor barrier around pot lights, electrical receptacles, floors, as well log or any other beams, posts or trusses that extend outward, plus windows and doors and any other sources of vapor barrier breach is time well spent and normally will reward one in energy cost savings within a relatively short period of time, greater than the cost of the labor and material to do it properly. Another approach worthy of considering is to use closed cell 2 lb. sprayed in foam insulation in your vaulted ceilings. Done properly it is its own vapor barrier with the highest of "R" values for its thickness.
Energy storage can be very valuable in housing. Energy (temperature) storage of any significance in conventional homes is normally limited to basement concrete slab floors, the foundation and possibly a masonry fireplace. Consider the stone wall style of architecture in climates that are hot during the day and cooler during the night as a basis for discussion about thermal mass. The thick rock walls do not have a great insulation value but they excel in mass. Climates where major temperature fluctuations occur, indoor temperatures can easily be moderated or entirely balanced by energy storage in a mass. Thick rock based walls (and fireplaces) can store large amounts of temperature, radiating back any difference to the indoor and outdoor temperatures surrounding those walls. In effect these walls almost act like a massive flywheel or battery trying to maintain the midpoint between the temperature fluctuations. Logs with enough mass will have a significant effect in trying to maintain that midpoint temperature. By volume wood does not have the same mass as many rock based construction materials, but mass is mass and given enough mass, logs would store similar amounts of energy. The greater the fluctuation in a shorter time frame such as daytime to nighttime the greater the benefit mass alone has in trying to maintain a midpoint temperature. Consider that when you combine the insulation value of wood with a good mass value found in larger logs, you have a factor not found in most other construction materials. Because the mass and insulation are combined in logs, the temperature is stored and radiated back over more beneficial periods of time than with rock. In the larger log, log walls this can add days of heat storage benefit offsetting a down turn in outdoor temperature. In fact, if you have a sufficiently insulated large enough mass also known as a heat sink, you could actually store enough excess summer heat to entirely heat your home in the winter. Where does mass alone have a diminishing value? In climates that have longer term consistent (colder or hotter) temperatures. In such climates the insulation factor tilts the scale on importance to more favor insulation. How can we maintain the midpoint of storage for temperature closer to a comfortable room temperature? There are a couple of ways that apply to log homes, the first is to have insulation between the outside temperature and the mass. As we know, logs do that naturally since wood is an insulator and a mass at the same time. The second applies to all forms of mass in colder climates and that is to store solar gain in the exterior of the walls. Daytime solar energy hitting log walls is stored in those walls helping to raise the wall temperature and offset some of the nighttime loss.
a) Obviously large windows facing north (in the northern hemisphere) can create a major heat loss. The very best windows normally used in residential construction may equal the lowest insulation value walls for energy loss. As good as windows and doors have become recently, they still are a major source of heat loss in the total building envelope. The difficult challenge to be achieved is to position windows in such a way that the total solar gain in the wintertime equals or exceeds the energy lost from those windows. (You likely will need to consider adding insulated curtains for the night time.) There is an important natural factor that helps this to occur. Even though weaker, the angle of the sun becomes closer to horizontal during the winter months. This has two benefits; the first is that the sun shines more under the roof eaves warming the log walls higher up as the angle of the sun is more perpendicular to the angle of the wall. This helps to raise the mean temperature of the log wall mass. The second is this angle also allows the solar energy to extend further into the rooms allowing more storage of that solar gain in everything from your floors to your furniture, making for a positive greenhouse effect. Also in the summer as the solar energy hits the windows as much as 35% is deflected away but in the winter the sun's angle is more perpendicular and less deflection occurs. A great design takes advantage of a good South (in the northern hemisphere) and Western exposure with generous roof overhangs that can also minimize the solar gain during the summer months. This aspect of a good design has far reaching benefits for log construction as it also greatly reduces maintenance by better protecting and increasing the longevity of the finish on and the logs themselves. Consider using clear glass without a titanium or the low "E" film and Argon gas if you want to increase the amount of solar gain on windows facing from Southeast to West (in the northern hemisphere). A potential disadvantage is that you will have more UV rays entering the home with the possibility of fading the floors or furniture associated with that UV sunlight however that is the same UV that indoor plants need to be able to survive.
b) Another design driven efficiency is maximizing your living space within a minimum of exterior surface area. Simply put, stacked floors are not only more cost effective to build but also heat lost through one level’s ceiling into another level’s floor is not actually heat lost from the house. While building a box may not be the most appealing design it often is one of the most energy efficient as you end up with one of the largest of interior space to the least exterior surface area ratios. I think that it is very important to balance efficiency with design flair. Keep in mind what first drew your desire towards building a log home.
c) Something else to consider in your design is the prevailing wind direction. Is there something you can do to redirect or avoid the wind such as choosing your location, tree planting or minimize the amount of home surface areas the wind has access to? Even a perfectly sealed building looses heat to wind that takes away heat that has radiated on or towards the exterior. Log buildings with notched corners have an advantage here in that the wind blowing along a wall is deflected away by the horizontal log overhangs extending past the corners. The logs in the wall with their irregular shapes reduce the effect of air movement and air currents thus reducing heat loss. These last two characteristics of log walls are harder to quantify exactly how much it benefits the energy requirements but it definitely is a benefit.
If your interests are to build off grid or to use any alternative energy as a heat source, efficiency is the first fundamental step you will need to address. It will make the difference in determining the feasibility of those alternative sources. The cost of producing solar or ground source heat (geothermal) is still significant, the more efficient your home the lower the amount of mechanical requirement and cost outlay and the sooner the payback. To check the energy efficiency of your construction, consider doing an infra-red thermal scan during the final stages of dry-in or lock-up where you are fully insulated but prior to vapor barrier installation. At this stage it can be easy to determine where you have any leaks or low insulation locations. We enjoy getting the feedback on how exceptionally well our patented log joinery is performing not only compared to other log products previously tested by the Thermographer but also in comparison to conventional construction. Feedback such as “in conventional housing you do see every stud, electrical receptacle and any poorly fitted insulation or vapor barrier breaks, but in a Moose Mountain log home the wall is amazingly uniform giving minimal indications of heat loss”.
In summary no matter how much insulation you can afford to use you will have some heat loss, in large log, log construction, for much of the year storing energy in the mass of the walls will offset a major amount of that heat loss. In addition, a good and efficient design may further offset much of what is lost by producing additional solar gain for that storage. When you apply everything presented here on sealing and insulating, plus passive solar, along with energy storage in the log wall mass into a great design, building a super energy efficient log home is a very realistic goal that all potential log home owners should seriously consider. A well built log home should be around for many, many generations with the additional bonus that you likely have the healthiest environment of any super energy efficient home being built today by using a far greater component of naturally renewable materials of the healthiest origin. If you consider what attracts people to build with logs in the first place, almost certainly it is the log home aesthetics, my opinion is no other form of construction can possibly offer so many exceptional benefits within such a beautiful package.
By Lloyd Beckedorf
For a technical
verification of the above please read the article in the link below.
The following is taken from the US Department of Energy, Energy Efficiency and Renewable Energy, Building Technologies Program: http://www.energycodes.gov/news/2005_workshop/presentations/cracker_barrel/r_pickett-en_perform_loghomes.pdf
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