Rubber stamped; a phrase that characteristically has a negative connotation meaning an action or product hasn’t been scrutinized for quality, safety and or appropriateness. On the converse side, a stamp or marking can mean that exactly those qualities are present. Construction material ratings and standards are very helpful, providing consistency and a level of safety when a structure is built or repaired. Construction grade wood products come from the factory with stamping that identifies their quality, use and strength. With plywood or OSB an APA (Engineered Wood Association) stamp denotes quality, product design use and performance.
While walking the roof of an older ranch style house, I noticed several spongy areas under my feet. Some were in places that I would expect water damage, others were not. That in and of it self was not unusual, as I said the house was older, so the roof covering could have been let go for many years past the time of needed replacement. The attic would hopefully fill in the blanks.
Finding the attic after descending from the roof, I entered through the small scuttle opening located in the hall closet. Initially scanning the area from the entry with my flashlight, I noted several areas of newer wood sheathing on the roof. Climbing in and looking closer I noticed the sheathing was bowing in many locations. That would explain the spongy roof. What was somewhat strange was the framing was 16" on center. With a wider span, 24", some deflection is "normal".
Being that the wood is newer, I would expect to see an APA grading stamp denoting the plywood's intended use and dimension. I could find none on any of the numerous sections of new wood. Yes the stamp is place on one side, so it could be on the covered portion. However, the stamp should be installed where it can be seen, for what would seem obvious reasons.
The other concern related to the soft roof surfaces is the sectioning of the new wood. The panels are rated for use as entire sheets or cut sections meeting stated specifications. According to the APA; "Panels are assumed continuous over two or more spans with the long dimension or strength axis across supports". One of the softer parts of the roof was found to be a section of plywood placed over a single span.
Without the stamp visible, assuming one is present at all, the grade of the wood used can only be guessed. However the evidence shows poor understanding of wood use and quality parameters and shoddy installation practices. The panels appear to be a low quality, general purpose plywood, not structural panels.
The roof covering was older and would require replacement in just a few years, therefore the recommendation was to remove the covering at that time, with the contractor assessing the sheathing and making repairs as deemed appropriate.