Small Crack In Roof Rafter
Whether you have a small crack or a large crack
in any structural framing component, you have a problem. The larger the
crack of course, the larger the problem.
In the picture above, the crack is hardly noticeable. The darker spot on the wood is actually a small knot in the roofer rafter and this one isn't very big. Just like the size of the crack, usually the larger than knot, the larger the problem can be.
This crack was caused from excessive structural weight directly above this roofer rafter. The builder or engineer should have called out for a larger sized roofer rafter, for example: I would've installed 3 - 2 x 6 roof rafters and nailed them together.
There are a few different things that can cause small cracks and one of them is old lumber, as lumber ages, the moisture from the wood will start to evaporate, causing the lumber to shrink.
If you live in extreme climates, where temperatures fluctuate from hot to cold, for example: during the day, temperatures are reaching well over 100° and in the evening, they're dropping below 40°, these temperature differences can cause the wood to contract during the day and absorb moisture in the evening, causing them to expand.
Over time you will have small and large cracks in your wood. Small cracks can also be caused by excessive weight over an individual framing member and lumber defects.
Home Repair Tip: Install another 2 x 6 roof rafter along each side of the cracked and damaged rafter. Make sure that you nail the three rafters together, using 16-D nails and stagger nailing them every 16 inches.
This is only a recommendation, you should contact a licensed building professional to evaluate a situation like this.