How to properly define standard overheads in manufacturing

Summary: in my manufacturing scenario i have variable and constant overheads, variable overheads being electricity, water, gas etc, which can be defined properly as plant overhead of type percentage from total work order cost. On the other hand, the constant overheads such as salaries, can’t be treated the same way, because regardless if the plant completed 1000 work orders or none per month, the salaries remain the same, so i can not treat it like the variable overhead. What would be a good solution for this issue?

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in my manufacturing scenario i have variable and constant overheads, variable overheads being electricity, water, gas etc, which can be defined properly as plant overhead of type percentage from total work order cost. On the other hand, the constant overheads such as salaries, can’t be treated the same way, because regardless if the plant completed 1000 work orders or none per month, the salaries remain the same, so i can not treat it like the variable overhead. What would be a good solution for this issue?