living trees contain sap, newly sawn timbers are very high in
moisture content. Moisture content within the timber varies greatly.
In softwoods the sapwood contains more moisture than the heartwood,
while in hardwoods the sapwood and the heartwood may have nearly
the same moisture content. Because softwoods have a lower moisture
content and are lighter than hardwoods they shrink less than hardwoods.
Among the softwoods Douglas Fir will shrink more than Sitka Spruce
in timber dimensions, during drying, are not equal in all directions,
change is greatest in the girth of the timber.
change in diameter is about half of that in the girth of the
change lengthwise is very small, about 2% of girth change.
difference in girth and diameter shrinkage rates induces tension
stress that often cause a lengthwise separation of the wood that
extends across the rings of annual growth, which is called a heart
check. Since a heart check only separates the wood cells they
usually do not affect the structural capacity of the timber. Heart
checks and shrinkage are primarily aesthetic problems. The only
ways to eliminate heart checking is to either remove the heart
of the tree from the timber or to kiln dry the timber.
only trees large enough, in North America, to produce free-of-heart
timber are trees such as the Douglas Fir, Sitka Spruce and Cedar
that grow in British Columbia. We source all of our old growth
wood from some of the finest specialty mills in British Columbia.
We also have access to salvaged timber. When using salvaged timber
the heart checks have already occurred, therefore, we can place
the checks towards the outside of the building where they will
not be seen.
second method is to dry the timbers. Conventional drying takes
anywhere from 6 to 8 weeks, but with new technology radio frequency/vacuum
(RF/V) kiln drying, the drying time can be reduced down to several
days. We have access to the largest RF/V kiln in North America.
It can dry any size of timber up to 40 feet in length. When placing
an order with a kiln we specify that the wood must be dried down
to the same moisture content as that expected inside the heated
building. Since Alberta's average moisture content level is one
of the lowest in North America kiln drying is desirable to eliminate
heart checking. Kiln drying is desirable for wood inside the heated
interior of most North American buildings. When ordering old growth
timber from British Columbia we often order free-of-heart RF/V
timber and the process of RF/V drying eliminate heart checking
and significantly reduce checking and splits, but they do not
completely eliminate small internal checks. There may still be
small internal checks, but nothing the size of heart checks.
majority of timber sawn in Alberta, and the rest of North America,
is boxed heart cut and is not kiln dried. Since these timbers
will heart check, they cost less than the old growth dried timber
available in British Columbia. For these timbers we have developed
a crack control method, similar to that used in the concrete industry.
This method helps to drive the heart checks towards the outside
of the building, where they will not be seen. Our crack control
method helps to minimize heart checks but may not eliminate them.
This work takes longer, but the extra effort ensures the highest
quality timber frame possible.
We also have
sources of seasoned reclaimed, standing dead and fire damaged