- Thermal Resistance
of the logs
- Effective Thermal Resistance
to our interpretations of information from the Canadian Construction
Materials Center and the Model National Energy Code (1997),
a 150mm milled log wall need not comply with effective thermal
resistance requirements, as trade off calculations for this
type of log structure are permitted.
For purposes of trade
off calculations, a 150mm milled log wall shall be taken as
RSI = 1.3. Round Scribed log walls shall be taken as RSI = 2.
SPF, (spruce, pine, fir) as the wood species.
In our 30 years of experience here at Laurentien Log Homes Ltd.,
with feedback from numerous log structures built and tested, we
can testify that the energy efficiency of a well built log home
is about the equivalent of a frame home built with a 2x6 wall
structure and batt insulation. All other factors being equal,
the heating costs of two comparable structures will be the same
and the comfort of the log home will be superior.
- For more complete information, please consult
- Technical guide for Milled-log Buildings,
report 13142 , Milled Log Houses report 13140 (5.2.1) and Model
National Energy Code of Canada for Houses (1997) (220.127.116.11)
- Canadian Construction Materials Center
- Ottawa (Ontario)
- Canada K1A 0R6
Other studies conducted
in some northern states of the USA showed that R-values may
be increased substantially to account for the thermal mass
storage and thermal lag of solid wood walls.
In 1991, the NAHB (National
Association of Home Builders) Research Center conducted a study
for the LHC (Log Homes Council). This study showed that
the thermal mass
of log walls significantly reduces energy use for heating
in cold climates. The study compared the actual energy use
by eight log homes and eight well insulated foam houses during
one winter. The houses were evenly divided between upstate
New-York and Montana. The study also compared the homes
actual energy consumption. The results led to the conclusion
that log homes are as energy efficient as frame houses, even
though the average R-value of the log walls was 44 percent
lower than the R-value of the frame walls.
More complete information
is available in the:
Research Report on Energy
Efficiency of Log Buildings published by the
- Log Homes Council National Association
of Home Builders
- 15th & M. Streets, N.W.
- Washington, D.C. 20005
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At LAURENTIEN Log Homes, the
pine is partially air dried at our factory and processed and installed
with 30% to 35% humidity throughout. It will still require 3 to
5 years to stabilize at the humidity level of the building area.
We dry the wood just long enough
to be able to put a nice finish on it. The major drying process
must take place after the wood is locked into place in the
wall, with the tons of weight and pressure locking it into place.
Our system was developed to take advantage of wood moisture and
our log wall structures will increase in strength and tightness
as they dry.
However, at LAURENTIEN Log Homes,
we can supply all of the following possibilities: Green, Air dried,
TO DRY OR NOT TO DRY
To those of you who are trying
to make the buying decision between kiln dried (KD) logs, air dried
or "green" logs, the dilemma seems without resolve. Of
course, a company who has kilns or access to kiln drying will probably
tell you the opposite truths of those companies who are convinced
that air dried or green wood serves the log home industry better.
In the following scenarios you may begin to see that as with many
other products in the marketplace, there is no miracle product that
will suit all situations and budgets.
In favor of KD wood
There are a number of advantages
to KD wood of course. The wood is much lighter, as much as forty
percent lighter than dead green timber. Lighter means cheaper shipping
costs and cheaper installation costs. The owner builders
will also appreciate lighter wood because he will require less manpower
for log installations, manpower which is oftentimes difficult to
come by when you really need it. Another advantage to dry timber
is that it is less susceptible to blue stain and other similar defacing
diseases. Also, dry wood will have been graded somewhat differently.
Certain defects which only show up after drying will already be
eliminated, for example wood which has twisted severely in a kiln
cannot be feasibly passed through any modern planer. KD wood is
normally ready for preservative treatment and or staining immediately
after or even before installation and generally, any bugs or molds
that could have been in the original timbers will be destroyed during
the drying process. It is a commonly accepted fact that KD lumber
will shrink less than air dried or green wood and this therefore
is one of the major marketing tools used in the log home industry.
In summary, the KD product is
lighter and more easily manipulated and has other positive properties
but these do not necessarily negate the benefits of air dried or
green lumber which is more commonly available.
Against KD wood
There are certain detrimental
aspects to the kiln drying issue as well. The KD log interface,
whose wood was hardened and stiffened by the drying process, cannot
have the same very low tolerance as an air dried log which is still
supple and flexible.
Just think about those couple
year old 2" x 4"s you may have hanging around the yard
and imagine trying to assemble three or four pieces of crooked dry
wood into a nice straight laminated piece. Imagine now how easy
it would be to make the same laminated piece with new pieces. The
point is: it is possible to bend a piece of board, green or dried.
But when you work with big timbers the difficulty increases, and
even more so with big KD timbers.
KD timber which is not properly
stored on site or in the suppliers yard is going to be very difficult
to work with. KD timber cannot be seated as tightly as fresh timber
therefore, although you may expect to have less wall shrinkage,
the difference may not be as great as was first thought. The wood
itself will definitely shrink less but the wall will have close
to as much shrinkage in height as an air dried log wall structure
because the joining along the log lengths will tighten up with time
and pressure. The person responsible for the construction of a log
home using KD timber must not be mislead into believing that the
shrinkage factor has been overcome. This is a common fallacy and
has lead to more than a few badly built homes.
Working with KD wood
Even though it is easier to
manipulate or lift KD timber, in general it is somewhat harder to
work with. It is easier to split dry wood when nailing if pre-drilling
is not done and it is necessary to work quickly before weather can
cause dimension changes in the wood. High humidity will cause a
certain amount of swelling which is not bad in itself but may cause
difficulty with certain tongue and groove systems.
The price of course is a factor
in any consumer item. Here we must calculate the savings on shipping
versus the extra cost of materials. Some savings may be obtained
in moving the wood about the site but this is probably offset by
extra expense in the actual installation of the pieces and extra
time spent on protection from the elements.
The exact moisture content
Purchasing logs which have only
been passed through a kiln meets perhaps the letter of a contract
but not the expectations of the buyer. For the first time buyer
considering KD versus air dried or green logs, it must be differentiated
clearly between what is kiln dried wood, air dried wood and green
The "buyer beware"
maxim applies only too aptly in this instance. When purchasing KD
logs, you must know to what percentage of humidity the complete
log has been dried, including and especially the heart of the log.
If your salesman comes across with a reply something to the effect
that their equipment can only test up to an inch or two of depth,
then we suggest that you look elsewhere for you KD logs.
This does not mean to expect
the impossible. What you should be aiming at is purchasing KD logs
with 15 per cent humidity; this would be ideal but unlikely. If
the wood is too dry it will be too hard to work with.
In the dry northern climates,
log walls will stabilize at around 12 per cent of humidity. In coastal
regions they will stabilize at around 15 per cent and, in the very
dry interior climates, at 9 or 10 per cent. A good supplier of KD
wall logs will be able to offer you complete information as to the
methods used to assure uniform quality of dryness in their logs
as well as the precautions and solutions used to deal with KD logs.
In favor of air dried or green wood.
The good supplier of air dried
or green wall logs will have the methods required to properly build
with his product. Air dried logs will be in the 20% to 30% range
and will have a number of checks and cracks to prove it whereas
dead green timber will be something over 30% and will not yet have
started any dimensional change.
The proof in all cases, whether
KD, air dried or green wood, is in the buildings themselves which
are five years or older. Ask questions to old customers, do an inspection
of a lived in home. Being the buyer, you are right to ask for proof:
seeing is believing. When all the information is in and you are
ready to buy, buy from the supplier who gives you what you want,
not from the supplier who gives you only the cheapest price.
If you can't afford what you
know you should be buying, wait! Don't buy anything!
One of the worst things that
can happen to a family is living in a dream home that they are unhappy
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