| The average conventionally constructed home yields an R value of 13. This includes wood siding, tyvek layer, 3 1/2 " of fiberglass insulation, 1/2 inch drywall and 1/2 inch plywood. VS A 12 inch thick log construction has an R value of 15.96. Plus the heat retaining capacities of thermal mass. |
| Log Homes vs Conventional Construction |
The following article was reprinted from BuildingGreen.com.
This website has a wealth of technical information on thermal efficiency.
Thermal Mass and R-value: Making Sense of a Confusing Issue. What effect does
thermal mass have on the energy performance of an exterior wall system? The issue
of thermal mass and its effect on the energy performance of buildings is one of the
most confusing issues facing designers, builders, and buyers of buildings today. This
article tries to sort out these mysteries, providing enough background on the physics
of heat transfer to understand the relationship between thermal storage and heat
flow, and then explaining when this information is relevant and how it should be
used in building design. This article does not address the use of thermal mass inside
a building, where it can store heat (or coolth) and even out temperature fluctuations.
Understanding Heat Transfer
Heat flows by three mechanisms: conduction, convection, and radiation. Conduction
is the molecule-to-molecule transfer of kinetic energy (one molecule becomes
energized and, in turn, energizes adjacent molecules). A cast-iron skillet handle
heats up because of conduction through the metal. Convection is the transfer of heat
by physically moving the molecules from one place to another. Hot air rises; heated
water thermosiphons; our forced-air heating systems work by moving hot air from
one place to another. Radiation is the transfer of heat through space via
electromagnetic waves (radiant energy). A campfire can warm you even if there is
wind between you and the fire, because radiation is not affected by air.
With buildings, we refer to heat flow in a number of different ways. The most
common reference is “R-value,” or resistance to heat flow. The higher the R-value of
a material, the better it is at resisting heat loss (or heat gain). U-factor (or “U-value,”
as it is often called) is a measure of the flow of heat—thermal transmittance—
through a material, given a difference in temperature on either side. In the inch-
pound (I-P) system, the U-factor is the number of Btus (British Thermal Units) of
energy passing through a square foot of the material in an hour for every degree
Fahrenheit difference in temperature across the material (Btu/ft2hr°F). In metric,
it’s usually given in watts per square meter per degree Celsius (w/m2°C).
R-values are measured by testing laboratories, usually in something called a guarded
hot box. Heat flow through the layer of material can be calculated by keeping one
side of the material at a constant temperature, say 90°F (32°C), and measuring how
much supplemental energy is required to keep the other side of the material at a
different constant temperature, say 50°F (10°C)—all this is defined in great detail in
ASTM (American Society of Testing and Materials) procedures. The result is a
steady-state R-value (“steady-state” because the difference in temperature across the
material is kept steady). R-value and U-factor are the inverse of one another: U = 1/R.
Materials that are very good at resisting the flow of heat (high R-value, low U-factor)
can serve as insulation materials. So far, so good.
Materials have another property that can affect their energy performance in certain
situations: heat capacity. Heat capacity is a measure of how much heat a material
can hold. The property is most significant with heavy, high-thermal-mass materials.
As typically used in energy performance computer modeling, heat capacity is
determined per unit area of wall. For each layer in a wall system, the heat capacity is
found by multiplying the density of that material, by its thickness, by its specific heat
(specific heat is the amount of heat a material can hold per unit of mass). Water has
a specific heat of 1 Btu/lb.°F (1.9 kJ/kg°C), while most building materials are around
0.2 to 0.3 Btu/lb.°F (0.4 to 0.6 kJ/kg°C).
If there are various layers in the wall, total heat capacity is found by adding up the
heat capacities for each layer (drywall, masonry block, and stucco, for example). In
the following section, we will examine how the heat capacity of materials can affect
the energy performance of buildings.
“Mass-Enhanced R-Value”
When people refer to the “mass effect” or “effective R-value,” they are generally
referring to the ability of high-mass materials, when used in certain ways, to achieve
better energy performance than would be expected if only the commonly accepted
(steady-state) R-value or U-factor of that material were considered. Let’s take a look
at a typical use of one of these high-mass materials in a wall system. When one side of
the wall is warmer than the other side, heat will conduct from the warm side into the
material and gradually move through it to the colder side. If both sides are at
constant temperatures—say the inside surface at 75°F (24°C) and the outside
surface at 32°F (0°C)—conductivity will carry heat out of the building at an easily
predicted rate. As described above, this steady-state heat flow is what most test
procedures for determining R-value measure.
In real-life situations, however, the inside and outside temperatures are not constant.
In fact, in many parts of the country, the driving force for conductive heat flow
(remember, heat always moves from warmer to colder) can change dramatically or
even reverse during the course of a day.
As noted above, the amount of heat flow through a wall is reduced by the use of
thermal mass when the temperatures fluctuate above and below the desired indoor
temperature, so under these conditions a material might have a “mass-enhanced” R-
value that is greater than its steady-state R-value. To estimate this mass-enhanced R-
value for a given high-mass material in a particular climate, researchers at Oak
Ridge National Laboratory measure the thermal performance of a high-mass wall
under
Clearly, high-mass materials used in exterior walls perform better than would be
expected based solely on their steady-state R-values. But the actual thermal
performance is highly dependent on where the building is located.
High-mass building materials can offer significant energy benefits in exterior walls.
The benefit may be primarily in the shifting of peak load conditions or in an actual
reduction in overall heat gain or loss.
This website has a wealth of technical information on thermal efficiency.
Thermal Mass and R-value: Making Sense of a Confusing Issue. What effect does
thermal mass have on the energy performance of an exterior wall system? The issue
of thermal mass and its effect on the energy performance of buildings is one of the
most confusing issues facing designers, builders, and buyers of buildings today. This
article tries to sort out these mysteries, providing enough background on the physics
of heat transfer to understand the relationship between thermal storage and heat
flow, and then explaining when this information is relevant and how it should be
used in building design. This article does not address the use of thermal mass inside
a building, where it can store heat (or coolth) and even out temperature fluctuations.
Understanding Heat Transfer
Heat flows by three mechanisms: conduction, convection, and radiation. Conduction
is the molecule-to-molecule transfer of kinetic energy (one molecule becomes
energized and, in turn, energizes adjacent molecules). A cast-iron skillet handle
heats up because of conduction through the metal. Convection is the transfer of heat
by physically moving the molecules from one place to another. Hot air rises; heated
water thermosiphons; our forced-air heating systems work by moving hot air from
one place to another. Radiation is the transfer of heat through space via
electromagnetic waves (radiant energy). A campfire can warm you even if there is
wind between you and the fire, because radiation is not affected by air.
With buildings, we refer to heat flow in a number of different ways. The most
common reference is “R-value,” or resistance to heat flow. The higher the R-value of
a material, the better it is at resisting heat loss (or heat gain). U-factor (or “U-value,”
as it is often called) is a measure of the flow of heat—thermal transmittance—
through a material, given a difference in temperature on either side. In the inch-
pound (I-P) system, the U-factor is the number of Btus (British Thermal Units) of
energy passing through a square foot of the material in an hour for every degree
Fahrenheit difference in temperature across the material (Btu/ft2hr°F). In metric,
it’s usually given in watts per square meter per degree Celsius (w/m2°C).
R-values are measured by testing laboratories, usually in something called a guarded
hot box. Heat flow through the layer of material can be calculated by keeping one
side of the material at a constant temperature, say 90°F (32°C), and measuring how
much supplemental energy is required to keep the other side of the material at a
different constant temperature, say 50°F (10°C)—all this is defined in great detail in
ASTM (American Society of Testing and Materials) procedures. The result is a
steady-state R-value (“steady-state” because the difference in temperature across the
material is kept steady). R-value and U-factor are the inverse of one another: U = 1/R.
Materials that are very good at resisting the flow of heat (high R-value, low U-factor)
can serve as insulation materials. So far, so good.
Materials have another property that can affect their energy performance in certain
situations: heat capacity. Heat capacity is a measure of how much heat a material
can hold. The property is most significant with heavy, high-thermal-mass materials.
As typically used in energy performance computer modeling, heat capacity is
determined per unit area of wall. For each layer in a wall system, the heat capacity is
found by multiplying the density of that material, by its thickness, by its specific heat
(specific heat is the amount of heat a material can hold per unit of mass). Water has
a specific heat of 1 Btu/lb.°F (1.9 kJ/kg°C), while most building materials are around
0.2 to 0.3 Btu/lb.°F (0.4 to 0.6 kJ/kg°C).
If there are various layers in the wall, total heat capacity is found by adding up the
heat capacities for each layer (drywall, masonry block, and stucco, for example). In
the following section, we will examine how the heat capacity of materials can affect
the energy performance of buildings.
“Mass-Enhanced R-Value”
When people refer to the “mass effect” or “effective R-value,” they are generally
referring to the ability of high-mass materials, when used in certain ways, to achieve
better energy performance than would be expected if only the commonly accepted
(steady-state) R-value or U-factor of that material were considered. Let’s take a look
at a typical use of one of these high-mass materials in a wall system. When one side of
the wall is warmer than the other side, heat will conduct from the warm side into the
material and gradually move through it to the colder side. If both sides are at
constant temperatures—say the inside surface at 75°F (24°C) and the outside
surface at 32°F (0°C)—conductivity will carry heat out of the building at an easily
predicted rate. As described above, this steady-state heat flow is what most test
procedures for determining R-value measure.
In real-life situations, however, the inside and outside temperatures are not constant.
In fact, in many parts of the country, the driving force for conductive heat flow
(remember, heat always moves from warmer to colder) can change dramatically or
even reverse during the course of a day.
As noted above, the amount of heat flow through a wall is reduced by the use of
thermal mass when the temperatures fluctuate above and below the desired indoor
temperature, so under these conditions a material might have a “mass-enhanced” R-
value that is greater than its steady-state R-value. To estimate this mass-enhanced R-
value for a given high-mass material in a particular climate, researchers at Oak
Ridge National Laboratory measure the thermal performance of a high-mass wall
under
Clearly, high-mass materials used in exterior walls perform better than would be
expected based solely on their steady-state R-values. But the actual thermal
performance is highly dependent on where the building is located.
High-mass building materials can offer significant energy benefits in exterior walls.
The benefit may be primarily in the shifting of peak load conditions or in an actual
reduction in overall heat gain or loss.
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| According to the national association of home builders: The resale value of conventional homes after 5 years will average 20% less than a log home in the same location. |
| Maintenance costs for a log home are less than conventional construction! By using the highest quality stains and sealants offered by Sikkens of Germany... |
| Our log homes provide an attractive and durable finish that will outlast any painted surface. No repainting of interior walls ever, just regular cleaning with a mild oil soap. Log homes are more resistant to structural damage than conventional structures. Feel safe and secure during storm season. The threat of high winds and falling trees is ever present. Flying debris that would destroy a conventional wall will bounce off a log home. |