Question: Is cracking down or splitting up like this normal?
I know this might seem extreme to you if you are not familiar with real wood products. This is why we recommend that you re-stain your pergola within the 1st year so that the wood has time to acclimate to the climate and then stain all the cracks. This is so common in timbers that there is a term for it called “Checking” which can seem to have the appearance of a split or a crack. Checking is a more common trait in Cedar timbers. A few of our clients still prefer Cedar especially in a Natural finish for its inherent beauty with knots. Here are pictures of checking from some of the displays in the show room at Western Timber Frame to show how common this is.
Timber is an organic, natural product and “checking” is to be expected. Checking is a natural lengthwise fissure of the wood/timber along the grain similar to a groove or fissure in an organ such as the brain. As timber/wood takes in or loses moisture, it shrinks and swells until it reaches its equilibrium with its constant changes to moisture levels in the air in its surrounding environment. All timber benefits from some seasoning, adjusting to its atmosphere and conditions.
For some, checking accentuates adding character and appeal with many examples such as in beams spanning ancient barn tops to grandly expansive cathedrals with handsomely exposed natural checking, reflecting the charm of nature. A timber frame shade structure does not lose its structural integrity once checking occurs.
Dougals-fir is a dimensionally stable, with the ability to stay well in position against stresses such as tension, compression and deflection. Douglas-fir is a species with a superior performance record having earned respect worldwide for its superior performance under extremely stressful conditions. With its incredible strength and strong, tough fibers Douglas Fir meets the test with weight and densely grained form and is the architectural choice for industrial and remanufacturing uses.