Log Home Basics
Log homes
may be site-built or pre-cut in a
factory for delivery to the site. Some
log home manufacturers can also
customize their designs. Before
designing or purchasing a manufactured
log
home, you need to consider the following
for energy efficiency:
The R-Value of Wood
In a log home, the wood helps provide
some insulation. Wood's thermal
resistance or resistance to heat flow is
measured by its R-value. The higher the
R-value, the more thermal resistance.
The R-value for wood ranges between 1.41
per inch (2.54 cm) for most softwoods
and 0.71 for most hardwoods. Ignoring
the benefits of the thermal mass, a
6-inch (15.24 cm) thick log wall would
have a clear-wall (a wall without
windows or doors) R-value of just over
8.
Compared to
a conventional wood stud wall [31 D2
inches (8.89 cm) insulation, sheathing,
wallboard, a total of about R-14] the
log wall is apparently a far inferior
insulation system. Based only on this,
log walls do not satisfy most building
code energy standards. However, to what
extent a log building interacts with its
surroundings depends greatly on the
climate. Because of the log's heat
storage capability, its large mass may
cause the walls to behave considerably
better in some climates than in others.
Logs act like "thermal batteries" and
can, under the right circumstances,
store heat during the day and gradually
release it at night. This generally
increases the apparent R-value of a log
by 0.1 per inch of thickness in mild,
sunny climates that have a substantial
temperature swing from day to night.
Such climates generally exist in the
Earth's temperate zones between the 15th
and 40th parallels.
Minimizing Air Leakage in Log
Homes
Log homes are susceptible to developing
air leaks. Air-dried logs are still
about 15–20% water when the house is
assembled or constructed. As the logs
dry over the next few years, the logs
shrink. The contraction and expansion of
the logs open gaps between the logs,
creating air leaks, which cause drafts
and high heating requirements. To
minimize air leakage, logs should be
seasoned (dried in a protected space)
for at least six months before
construction begins. These are the best
woods to use to avoid this problem, in
order of effectiveness:
-
Cedar
- Spruce
- Pine
- Fir
- Larch
Since most
manufacturers and experienced builders
know of these shrinkage and resulting
air leakage problems, many will kiln dry
the logs prior to finish shaping and
installation. Some also recommend using
plastic gaskets and caulking compounds
to seal gaps. These seals require
regular inspection and resealing when
necessary.
Controlling Moisture in Log
Homes
Since trees absorb large amounts of
water as they grow, the tree cells are
also able to absorb water very readily
after the wood has dried. For this
reason, a log home is very
hydroscopic—it can absorb water quickly.
This promotes wood rot and insect
infestation. It is strongly recommended
that you protect the logs from any
contact with any water or moisture. One
moisture control method is to use only
waterproofed and insecticide-treated
logs. Reapply these treatments every few
years for the life of the house.
Generous roof overhangs, properly sized
gutters and downspouts, and drainage
plains around the house are also
critical for moisture control.
Building Energy Code Compliance for Log
Homes
Because log homes don't have
conventional wood-stud walls and
insulation, they often don't satisfy
most building code energy
standards—usually those involving
required insulation R-values.
However, several states—including
Pennsylvania, Maine, and South
Carolina—have exempted log-walled homes
from normal energy compliance
regulations. Others, such as Washington,
have approved "prescriptive packages"
for various sizes of logs, but these may
or may not make sense in terms of energy
efficiency. The American Society of
Heating, Refrigerating, and Air
Conditioning Engineers (ASHRAE) 90.2
standard contains a thermal mass
provision that may make it easier to get
approval in those states that base their
codes on this standard. To find out the
log building code standards for your
state, contact your city or county
building code officials. Your state
energy office may be able to provide
information on energy codes recommended
or enforced in your state.
Building & Restoration of
Log Cabins
Foundation
The foundation of a log cabin is
made of stone pillars. The stones
provide a sturdy base to support the
cabin and act as a barrier between
the cabin and the earth. The stones
may settle over time and the
foundation is carefully examined for
damage or wear and subsequently
repaired during restoration.
Wall Construction
The walls are made of logs, placed
either vertically or horizontally,
depending on the style and size of
the cabin. The logs are notched at
the corners to allow them to fit
together. Corner notching is a
notable characteristic of log cabin
construction because it provides
stability by locking the log ends in
place, enabling the logs to fit
together in a secure manner. Many
different methods of corner notching
exist, ranging from simple "saddle"
notching to the common "V" notching
or "steeple" notching, which get
their name from the shape of the
notch cut into the wood. These
notching methods are marked by a cut
into the wood that allows another
cut piece of wood to fit together
like a puzzle piece. Another
commonly used technique, "square"
notching, differs in that the logs
are secured with the addition of
pegs or spikes.
The
number of logs used per wall varies
with the size of the cabin. The
spaces between logs are usually
filled with a combination of
materials in a process known as
"chinking" and "daubing." This
process seals the exterior walls,
protecting them from weather and
animal damage.
Roof
Log cabin roofs are often gabled and
are comprised of hand-split, wood
shingles. The roofs often develop
damage and leaks over the years and
are commonly included in
restoration.
Doors
Many
log cabins have both a front and
rear door. Due to the many times
the doors are opened and closed
over the years, the doors are
often not in good working order
and require repair during
restoration. Both doors on the
cabin can be comprised of boards
that are hand-dressed, open
inward and are fastened to the
log structure with pegs.
Windows
The cabin features two windows,
located on either side of the
chimney. The windows hold glass
panes, which most likely need to
be replaced during the
restoration of the cabin.
Chimney
The
cabin has a chimney that sank
and deteriorated into many
different pieces over the years.
The chimney was rebuilt during
cabin restoration.
Definitions:
Handcrafted log home
A home that
is constructed of logs that are
individually fit together.
Milled log home
Constructed
of machine-lathed logs, and is also used
to describe a log home built from a kit.
Insulated log home
Constructed
with half-logs attached to a standard
2x6 frame structure.
Chinking
The mixture
used to fill the gaps between logs - can
be natural materials or synthetic.
Shrinking
The normal
loss of diameter in logs as they lose
moisture.
Settlement
The downward
movement of log courses as the logs
shrink.
Checking
The natural
cracking of logs as they shrink.
Butt
joints
Occur when
two logs are placed end-to-end.
Log
course
One layer of
logs placed atop the entire foundation
of the home.
Log
wall exterior
The inspector shall inspect exterior
surfaces of log walls, when such
surfaces are visible, looking for:
-
presence of mold, mildew or fungus
- cracks located at
tops of logs and facing up
- discoloration,
graying, bleaching or staining of
logs
- loose or missing
caulking
- separation of
joints
- condition of
chinking, to include cracking,
tears, holes, or separation of log
courses
- condition of log
ends
Log
wall interior
The inspector shall inspect interior
surfaces of log walls, when such
surfaces are visible, looking for:
-
separation between logs, including
light or air penetration from
outdoors
- separation
between exterior log wall and
interior partition walls
- separation
between log walls and interior
ceilings
Other exterior concerns
In addition to the items specified in
NACHI Standards of Practice 2.1 and 2.2,
the inspector shall inspect:
-
downspout extensions
- grading and water
flow away from log walls
- vertical support
posts under and on all porches
Other interior concerns
In addition to the items specified in
NACHI Standards of Practice 2.4 and 2.6,
the inspector shall inspect:
- Slip
joints, adjustable sleeves, looped
water supply lines, flexible hose
sections, and flexible ductwork that
are visible as part of the standard
heating and plumbing inspections.
Exclusions
The inspector is not required to:
-
inspect or predict the condition of
the interiors of logs
-
predict the life expectancy of logs
- climb onto log
walls. However, the inspector may
inspect log walls by use of a
ladder, if this procedure may be
done safely and without damaging the
walls.
-
inspect components of the porch
support system, or of the plumbing
or heating systems, that are not
readily visible and accessible.
