While wood can be used for lintels in certain applications, it may not be the most suitable choice for your specific scenario. Building codes and regulations can vary by location, so it's important to consult with a local building professional or structural engineer to ensure compliance with the requirements in your area.
That being said, there are a few factors to consider when determining the appropriate material for a lintel over a sliding glass door on a block wall:
Strength and load-bearing capacity: Even though you mentioned there will be no load above the lintel, it's still important to ensure that the lintel can adequately support the weight of the sliding glass door and any additional forces acting on it, such as wind loads. Wood may have limitations in terms of its structural strength and durability, especially when exposed to the elements over time.
Moisture and rot resistance: Florida's humid and often rainy climate can pose challenges for wood, as it is susceptible to moisture absorption and rot. Proper treatment and protection measures would be necessary to prevent potential damage and ensure the longevity of the lintel.
Code compliance: Local building codes and regulations will dictate the acceptable materials for lintels, particularly in terms of fire resistance and structural requirements. It's crucial to consult with a professional to ensure compliance with these codes.
Given these considerations, alternative materials such as steel lintels or reinforced concrete lintels might be more commonly used and provide better long-term performance and structural stability in Florida's climate. A professional can assess your specific situation and provide appropriate recommendations based on local building codes and engineering standards.