Some people mention it creates a "weak point" or how the rafters may "split" up the board and having the strnegth of 2 x 4 instead of a 2 x 8, however I do not understand how this would happen.
Re-entrant splits in lumber can also occur specifically after cutting a rafter bird's mouth. A rafter bird's mouth is a notch or cut made on the underside of a rafter to fit securely onto a wall or support structure.
When cutting a bird's mouth, the notch removes a portion of the wood at the end of the rafter, leaving a triangular-shaped cutout. This cutout weakens the structural integrity of the wood in that area, making it more susceptible to splitting.
Re-entrant splits in this context refer to the splits that originate from the cut end of the rafter and extend inward along the grain. These splits typically follow the triangular shape of the bird's mouth cut and can occur due to a combination of factors.
One of the primary factors contributing to re-entrant splits after cutting a rafter bird's mouth is the release of internal stresses within the wood. Wood naturally contains moisture and stress within its fibers. When a bird's mouth is cut, the removal of wood can cause the release of these internal stresses, leading to the wood splitting along the grain.
The likelihood of re-entrant splits can also be influenced by the quality and characteristics of the lumber itself. Wood species that are more prone to splitting, such as those with high density or a tendency to shrink or expand significantly, are more susceptible. Additionally, wood that is not properly dried or seasoned may have higher moisture content, increasing the risk of splitting.
To minimize the occurrence of re-entrant splits after cutting a rafter bird's mouth, it is important to use appropriate techniques and considerations. Here are some recommendations:
- Use properly seasoned and dried lumber: Ensure that the wood used for rafters has been properly dried to an appropriate moisture content level. This can help reduce the risk of splitting.
- Make precise and clean cuts: Use sharp and appropriate tools to make clean and accurate cuts. This can minimize the amount of stress and damage to the wood fibers, reducing the likelihood of splits.
- Provide additional support: Reinforcing the area around the bird's mouth with additional fasteners, such as nails or screws, can help distribute the load and reduce stress concentration, thereby decreasing the chances of splitting.
- Apply protective coatings: Applying appropriate wood preservatives or sealants to the cut ends of the rafter can help reduce moisture absorption and minimize the risk of splitting.
- Drill a hole at the inside corner and cut into the hole.
#5 is me. Isn't this just a hoot! Academia as we know it is on it's way out. You can all be Vegas Paul....well except for the murdering part....that's still a hands on task.
